IPCS INCHEM Home



    INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY



    ENVIRONMENTAL HEALTH CRITERIA 149





    CARBENDAZIM









    This report contains the collective views of an international group of
    experts and does not necessarily represent the decisions or the stated
    policy of the United Nations Environment Programme, the International
    Labour Organisation, or the World Health Organization.

    Published under the joint sponsorship of
    the United Nations Environment Programme,
    the International Labour Organisation,
    and the World Health Organization

    First draft prepared by IPCS staff, using texts made available
    by Dr L.W. Hershberger and Dr G.T. Arce, Wilmington, Delaware, USA

    World Health Orgnization
    Geneva, 1993


         The International Programme on Chemical Safety (IPCS) is a
    joint venture of the United Nations Environment Programme, the
    International Labour Organisation, and the World Health
    Organization. The main objective of the IPCS is to carry out and
    disseminate evaluations of the effects of chemicals on human health
    and the quality of the environment. Supporting activities include
    the development of epidemiological, experimental laboratory, and
    risk-assessment methods that could produce internationally
    comparable results, and the development of manpower in the field of
    toxicology. Other activities carried out by the IPCS include the
    development of know-how for coping with chemical accidents,
    coordination of laboratory testing and epidemiological studies, and
    promotion of research on the mechanisms of the biological action of
    chemicals.

    WHO Library Cataloguing in Publication Data

    Carbendazim.

        (Environmental health criteria ; 149)

        1.Benzimidazoles - adverse effects 2.Benzimidazoles - toxicity
        3.Fungicides, Industrial - adverse effects 4.Fungicides, Industrial
        -toxicity  I.Series

        ISBN 92 4 157149 7        (NLM Classification: WA 240)
        ISSN 0250-8634

         The World Health Organization welcomes requests for permission
    to reproduce or translate its publications, in part or in full.
    Applications and enquiries should be addressed to the Office of
    Publications, World Health Organization, Geneva, Switzerland, which
    will be glad to provide the latest information on any changes made
    to the text, plans for new editions, and reprints and translations
    already available.

    (c) World Health Organization 1993

         Publications of the World Health Organization enjoy copyright
    protection in accordance with the provisions of Protocol 2 of the
    Universal Copyright Convention. All rights reserved.

         The designations employed and the presentation of the material
    in this publication do not imply the expression of any opinion
    whatsoever on the part of the Secretariat of the World Health
    Organization concerning the legal status of any country, territory,
    city or area or of its authorities, or concerning the delimitation
    of its frontiers or boundaries.

         The mention of specific companies or of certain manufacturers'
    products does not imply that they are endorsed or recommended by the
    World Health Organization in preference to others of a similar
    nature that are not mentioned. Errors and omissions excepted, the
    names of proprietary products are distinguished by initial capital
    letters.





    CONTENTS

    ENVIRONMENTAL HEALTH CRITERIA FOR CARBENDAZIM

    1. SUMMARY AND CONCLUSIONS

         1.1. Summary
               1.1.1. Identity, physical and chemical properties, and
                      analytical methods
               1.1.2. Sources of human and environmental exposure
               1.1.3. Environmental transport, distribution and
                      transformation
               1.1.4. Environmental levels and human exposure
               1.1.5. Kinetics and metabolism
               1.1.6. Effects on laboratory mammals and  in vitro
                      test systems
               1.1.7. Effects on humans
               1.1.8. Effects on other organisms in the laboratory
                      and field
         1.2. Conclusions

    2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND ANALYTICAL
         METHODS

         2.1. Identity
               2.1.1. Primary constituent
               2.1.2. Technical product
         2.2. Physical and chemical properties
         2.3. Analytical methods

    3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

         3.1. Natural occurrence
         3.2. Anthropogenic sources
               3.2.1. Uses

    4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION

         4.1. Transport and distribution between media
               4.1.1. Air
               4.1.2. Water
               4.1.3. Soil
               4.1.4. Leaching
               4.1.5. Crop uptake
         4.2. Transformation
               4.2.1. Soil biodegradation
               4.2.2. Abiotic degradation
               4.2.3. Bioaccumulation

    5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

         5.1. Environmental levels
               5.1.1. Air, water and soil
               5.1.2. Food and feed
               5.1.3. Terrestrial and aquatic organisms
         5.2. General population exposure
               5.2.1. Sweden
               5.2.2. The Netherlands
               5.2.3. National maximum residue limits
         5.3. Occupational exposure during manufacture,
               formulation, or use
               5.3.1. Exposure during manufacture
               5.3.2. Exposure during use

    6. KINETICS AND METABOLISM

         6.1. Absorption
         6.2. Distribution and accumulation
         6.3. Metabolic transformation
         6.4. Elimination and excretion
         6.5. Reaction with body components

    7. EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS

         7.1. Single exposure
         7.2. Short-term exposure
               7.2.1. Gavage
               7.2.2. Feeding
                      7.2.2.1 Rat
                      7.2.2.2 Dog
               7.2.3. Dermal
         7.3. Skin and eye irritation; sensitization
               7.3.1. Dermal
               7.3.2. Eye
               7.3.3. Sensitization
         7.4. Long-term exposure
               7.4.1. Rat
               7.4.2. Dog
               7.4.3. Mouse
         7.5. Reproduction, embryotoxicity and teratogenicity
               7.5.1. Reproduction
               7.5.2. Embryotoxicity and teratogenicity
         7.6. Mutagenicity and related end-points
         7.7. Carcinogenicity
         7.8. Neurotoxicity
         7.9. Toxicity of contaminants
         7.10. Mechanisms of toxicity - mode of action

    8. EFFECTS ON HUMANS

         8.1. General population exposure
         8.2. Occupational exposure

    9. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD

         9.1. Microorganisms
         9.2. Aquatic organisms
         9.3. Terrestrial organisms
         9.4. Population and ecosystem effects

    10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON ENVIRONMENT 95

         10.1. Evaluation of human health risks
         10.2. Evaluation of effects on the environment
         10.3. Conclusions

    11. FURTHER RESEARCH

    12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

    REFERENCES

    RESUME ET CONCLUSIONS

    RESUMEN Y CONCLUSIONES
    

    WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR BENOMYL AND
    CARBENDAZIM

     Members

    Dr G. Burin, Office of Pesticide Programmes, US Environmental
         Protection Agency, Washington, D.C., USA

    Dr R. Cooper, Reproductive Toxicology Branch, US Environmental
         Protection Agency, Research Triangle Park, North Carolina, USA

    Dr I. Desi, Department of Public Health, Albert Szent-Györgyi
         University Medical School, Szeged, Hungary

    Dr S. Dobson, Institute of Terrestrial Ecology, Monks Wood, Abbots
         Ripton, Huntingdon, United Kingdom

    Dr A. Helweg, Department for Pesticide Analysis and Ecotoxicology,
         Danish Research Service for Plant and Soil Science,
         Flakkebjerg, Slagelse, Denmark

    Dr M. Lotti, Institute of Occupational Medicine, University of
         Padua, Padua, Italy  (Chairman)

    Dr K. Maita, Toxicology Division, Institute of Environmental
         Toxicology, Kodaira-Shi, Tokyo, Japan

    Dr F. Matsumura, Department of Environmental Toxicology, Institute
         of Toxicology and Environmental Health, University of
         California, Davis, California, USA

    Dr T.K. Pandita, Microbiology and Cell Biology Laboratory, Indian
         Institute of Science, Bangalore, Indiaa

    Dr C. Sonich-Mullin, Environmental Criteria and Assessment Office,
         US Environmental Protection Agency, Cincinnati, Ohio, USA

    Dr P.P. Yao, Institute of Occupational Medicine, Chinese Academy of
         Preventive Medicine, Beijing, China

     Secretariat

    Dr B.H. Chen, International Programme on Chemical Safety, World
         Health Organization, Geneva, Switzerland ( Secretary)

    Dr L.W. Hershberger, Dupont Agricultural Products, Walker's Mill,
         Barley Mill Plaza, Wilmington, Delaware, USA

    Mr P. Howe, Institute of Terrestrial Ecology, Monks Wood, Abbots
         Ripton, Huntington, United Kingdom

    a Invited but unable to attend the meeting

    NOTE TO READERS OF THE CRITERIA MONOGRAPHS

         Every effort has been made to present information in the
    criteria monographs as accurately as possible without unduly
    delaying their publication. In the interest of all users of the
    Environmental Health Criteria monographs, readers are kindly
    requested to communicate any errors that may have occurred to the
    Director of the International Programme on Chemical Safety, World
    Health Organization, Geneva, Switzerland, in order that they may be
    included in corrigenda.

                                    * * *

         A detailed data profile and a legal file can be obtained from
    the International Register of Potentially Toxic Chemicals, Palais
    des Nations, 1211 Geneva 10, Switzerland (Telephone No. 7988400 or
    7985850).

    ENVIRONMENTAL HEALTH CRITERIA FOR CARBENDAZIM

         A WHO Task Group on Environmental Health Criteria for Benomyl
    and Carbendazim, sponsored by the US Environmental Protection
    Agency, met in Cincinnati, USA, from 14 to 19 September 1992. On
    behalf of the host agency, Dr T. Harvey opened the meeting and
    welcomed the participants. Dr B.H. Chen of the International
    Programme on Chemical Safety (IPCS) welcomed the participants on
    behalf of the Director, IPCS, and the three IPCS cooperating
    organizations (UNEP/ILO/WHO). The Task Group reviewed and revised
    the draft criteria monograph and made an evaluation of the risks for
    human health and the environment from exposure to carbendazim.

         The first draft of this monograph was prepared by the staff of
    IPCS, using texts made available by Dr L.W. Hershberger and Dr G.T.
    Arce, Wilmington, Delaware, USA. The second draft was prepared by Dr
    L.W. Hershberger and Dr B.H. Chen incorporating comments received
    following the circulation of the first draft to the IPCS Contact
    Points for Environmental Health Criteria monographs. Dr M. Lotti
    (Institute of Occupational Medicine, University of Padua, Italy)
    made a considerable contribution to the preparation of the final
    text. Dr B.H. Chen and Dr P.G. Jenkins, both members of the IPCS
    Central Unit, were responsible for the overall scientific content
    and technical editing, respectively.

         The efforts of all who helped in the preparation and
    finalization of the monograph are gratefully acknowledged.

         Financial support for the meeting was provided by the US
    Environmental Protection Agency, Cincinnati, USA.

    ABBREVIATIONS

    a.i.           active ingredient

    BSP            Bromosulfophthalein

    HPLC           high-performance liquid chromatography

    Koc            Distribution coefficient between pesticide adsorbed
                   to soil organic carbon and pesticide in solution

    Kom            Distribution coefficient between pesticide adsorbed
                   to soil organic matter and pesticide in solution

    NOEC           no-observed-effect concentration

    NOEL           no-observed-effect level

    2-AB           2-aminobenzimidazole

    5-HBC          methyl (5-hydroxy-1H-benzimidazol-2-yl)-carbamate

    1.  SUMMARY AND CONCLUSIONS

    1.1  Summary

    1.1.1  Identity, physical and chemical properties, and analytical
           methods

         Carbendazim, a white crystalline solid, is a systemic fungicide
    belonging to the benzimidazole family. It melts at approximately 250
    °C and has a vapour pressure of < 1 x 10-7 Pa (< 1 x 10-9
    mbar) at 20 °C. Carbendazim is essentially insoluble in water (8
    mg/litre solubility) at pH 7 and 20 °C. It is stable under normal
    storage conditions.

         Residual and environmental analyses are performed by extraction
    with an organic solvent and the extract is purified by a
    liquid-liquid partitioning procedure. Measurement of residues may be
    determined by HPLC or immunoassay.

    1.1.2  Sources of human and environmental exposure

         Carbendazim is the most widely used member of the benzimidazole
    family of fungicides. It is formulated as an aqueous dispersion,
    aqueous suspension, flowable water-dispersible granule and a
    wettable powder.

    1.1.3  Environmental transport, distribution and transformation

         Benomyl is rapidly converted to carbendazim in the environment,
    with half-lives of 2 and 19 h in water and in soil, respectively.
    Data from studies on both benomyl and carbendazim are therefore
    relevant for the evaluation of environmental effects.

         Carbendazim is decomposed in the environment with half-lives of
    6 to 12 months on bare soil, 3 to 6 months on turf, and half-lives
    in water of 2 and 25 months under aerobic and anaerobic conditions,
    respectively. Carbendazim is mainly decomposed by microorganisms;
    2-aminobenzimidazole (2-AB) is the major degradation product and is
    further decomposed by microbial activity. When phenyl-14C-labelled
    benomyl was decomposed, only 9% of the 14C label was evolved in
    CO2 during 1 year of incubation, the remaining 14C being
    recovered mainly as carbendazim and bound residues. The fate of a
    possible degradation product (1,2-diaminobenzene) may shed further
    light on the degradation pathway of benzimidazole fungicides in the
    environment.

         Field and column studies have shown that carbendazim remains in
    the soil surface layer. No determination of carbendazim adsorption
    in soil is available, but it is likely to be as strongly adsorbed to
    soil as benomyl (Koc values ranking from 1000 to 3600). Log Kow
    values for benomyl and carbendazim are 1.36 and 1.49, respectively.

         A risk of leaching was not apparent when this was evaluated in
    a screening model based on adsorption and persistence data. This
    statement is supported by analysis of well water in the USA, where
    carbendazim has not been found in any of 212 wells (limit of
    detection not available). Surface run-off of benomyl and carbendazim
    is expected to consist only of fungicide adsorbed to soil particles,
    and the fungicides are likely to be strongly adsorbed to sediments
    in the aqueous environment.

         Carbendazim is hydrolysed to 2-AB. This is also the primary
    metabolite in soil and plants.

         In animal systems, carbendazim is metabolized to (5-hydroxy-
    1H-benzimidazol-2-yl)-carbamate (5-HBC) and other polar metabolites,
    which are rapidly excreted. Carbendazim has not been observed to
    accumulate in any biological system.

    1.1.4  Environmental levels and human exposure

         There appear to be no environmental monitoring data for
    carbendazim. However, the following can be summarized from
    environmental fate studies.

         Due to the fact that they are stable for several weeks on plant
    material, benomyl and carbendazim may become accessible to organisms
    feeding on leaf litter. Soil and sediments may contain residues of
    carbendazim for up to 3 years. However, the strong adsorption of
    carbendazim to soil and sediment particles reduces the exposure for
    terrestrial and aquatic organisms.

         Primary exposure for the general human population will be from
    residues of benomyl and carbendazim on food crops. Dietary exposure
    analysis in the USA (combined benomyl and carbendazim) and the
    Netherlands (carbendazim) estimated the expected mean intake to be
    about one-tenth of the recommended Acceptable Daily Intake (ADI) of
    0.02 mg/kg body weight for benomyl and 0.01 mg/kg body weight for
    carbendazim.

         Occupational exposure during manufacture is below the Threshold
    Limit Value established for benomyl. Agricultural workers engaged in
    pesticide mixing and loading or in re-entering benomyl-treated
    fields are expected to be exposed to dermal contact of a few mg
    benomyl per h. This type of exposure could be reduced by the use of
    protective devices. Furthermore, since dermal absorption is expected
    to be low, the probability of systemic toxicity of benomyl through
    this route is very low.

    1.1.5  Kinetics and metabolism

         Carbendazim is well absorbed (80-85%) after oral exposure but
    much less so by dermal exposure. Absorbed carbendazim is metabolized

    into many compounds within the organism. The main metabolites are
    5-HBC and 5,6-HOBC-N-oxides. Minor metabolites are 5,6-DHBC-S and
    5,6-DHBC-G.

         The tissue distribution of carbendazim showed no
    bioconcentration. In the rat, the highest concentration after oral
    carbendazim administration (< 1% of the dose) occurred in the
    liver. It was distributed as carbendazim in the mitochondria, 5-HBC
    in the cytostol, and 2-AB in the microsomes. Carbendazim and its
    metabolites were also found in the kidney of hens and cows; but no
    significant levels were detected in other tissues. After carbendazim
    was fed to lactating cows, small amounts of 5-HBC and 4-HBC were
    found in the milk.

         Carbendazim is excreted in the urine and faeces within 72 h
    after oral dosing in rats.

         In rats and mice, high doses of carbendazim, both in the diet
    and by gavage, affect certain liver microsomal enzymes. Styrene-7,8-
    hydrolase and epoxide hydrolase were induced whereas 7-
    hydroxycoumarin O-deethylase activity was found to be reduced.
    Cytosolic glutathione S-transferase activity was also induced.

    1.1.6  Effects on laboratory mammals and in vitro test systems

    1.1.6.1  Single exposure

         Carbendazim has low acute toxicity. The LD50 values range
    from > 2000 to 15 000 mg/kg in a wide variety of test animals and
    routes of administration. However, significant adverse reproductive
    effects have been noted following a single exposure (see section
    1.1.6.5).

    1.1.6.2  Short-term exposure

         Dietary administration of carbendazim for up to 90 days
    produced slight effects on liver weight in female rats exposed to
    360 mg/kg body weight per day. In a 90-day gavage study in the rat,
    the NOEL was 16 mg/kg per day based on hepatotoxicity. Short-term
    feeding studies on dogs were not adequate for establishing a NOEL. A
    10-day dermal study in the rabbit revealed no systemic toxicity at
    the only dose tested (200 mg/kg).

    1.1.6.3  Skin and eye irritation and sensitization

         Application to the skin of the rabbit and guinea-pig produced
    no irritation or skin sensitization. Application to the eyes of
    rabbits produced moderate or mild conjunctival irritation.

    1.1.6.4  Long-term exposure

         Male and female rats fed 2500 mg/kg diet showed reduced
    erythrocyte count and haemoglobin and haematocrit values. No
    liver-related toxicity was noted. Male rats fed 2500 mg/kg diet or
    more presented a marginal increase in diffuse testicular atrophy and
    prostatitis. The NOEL in the rat is 500 mg/kg diet. Elevated serum
    cholesterol and alkaline phosphatase activity and other indications
    of hepatotoxicity were observed in dogs fed a diet containing 500 mg
    carbendazim/kg for 1 year or longer. The NOEL in the dog is 300
    mg/kg diet.

         Male and female mice fed 5000 mg/kg diet showed increased
    absolute liver weight. There was also significant centrilobular
    hypertrophy, necrosis and swelling of the liver in male mice fed
    1500 mg/kg diet.

    1.1.6.5  Reproduction, embryotoxicity and teratogenicity

         Carbendazim was without adverse effects on reproduction when it
    was fed to rats in a three-generation reproduction study at levels
    up to and including 500 mg/kg diet. Male fertility was depressed in
    rats when carbendazim (200 mg/kg per day) was administered by gavage
    for 85 days. A dose of 50 mg/kg body weight per day in this study
    caused a significant decrease in epididymal sperm count.

         Following a single oral dose to rats, histological examination
    revealed early (0-2 days) disruption of spermatogenesis with
    occlusion of efferent ducts and increased testicular weights at 100
    mg/kg body weight. No effect was observed at 50 mg/kg in this single
    dose study. These effects persisted until day 70 in rats treated
    with 400 mg/kg.

         Carbendazim caused an increase in malformations and anomalies
    in rats when administered at daily dose levels greater than 10 mg/kg
    on days 7-16 of gestation. There was a slightly decreased rate of
    implantation in rabbits administered 20 and 125 mg/kg per day on
    days 7-19 of gestation and an increased incidence of resorption at
    125 mg/kg per day. Maternal toxicity was observed at 20 mg/kg per
    day and 125 mg/kg per day in the rat and rabbit, respectively.

         In addition to decreased pregnancy rate and increased early
    resorptions in the rat, there were significant reductions in fetal
    weights at 20 and 90 mg/kg per day and a significant increase in
    fetal malformations at 90 mg/kg per day. These consisted primarily
    of hydrocephaly, microphthalmia, anophthalmia, malformed scapulea
    and axial skeletal malformations (vertebral, rib and sternebral
    fusions, exencephaly, hemivertebrae and rib hyperplasia). However,
    in the rabbit there were no significant malformations.

    1.1.6.6  Mutagenicity and related end-points

         Assays in mammalian and non-mammalian systems  in vitro and
     in vivo and in somatic cells as well as in germ cells show that
    carbendazim does not interact with DNA, induce point mutation or
    cause germ cell mutation.

         Carbendazim does, however, cause numerical chromosome
    aberrations (aneuploidy and/or polyploidy) in experimental systems,
    both  in vitro and  in vivo.

    1.1.6.7  Carcinogenicity

         Benomyl and carbendazim feeding resulted in an increase in the
    incidence of hepatocellular tumours in CD-1 and SPF Swiss mice.

         A carcinogenicity study of carbendazim using CD-1 mice showed a
    statistically significant dose-related increase in the incidence of
    hepatocellular neoplasia in females. There was also a statistically
    significant increase in the mid-dose (1500 mg/kg diet) males, but
    not in the high-dose males because of a high mortality rate. A
    carcinogenicity study of carbendazim in a genetically related mouse
    strain, SPF mice (Swiss random strain) at doses of 0, 150, 300 and
    1000 mg/kg diet (increased to 5000 mg/kg during the study) showed an
    increase in the incidence of combined hepatocellular adenomas and
    carcinomas. A study carried out in NMRKf mice at dose levels of 0,
    50, 150, 300 and 1000 mg/kg diet of carbendazim (increased to 5000
    mg/kg during the study) showed no carcinogenic effects. Benomyl or
    carbendazim caused liver tumours in two strains of mice (CD-1 and
    SPF), both of which have a high spontaneous rate of liver tumours.
    In contrast, carbendazim is not carcinogenic in NMRKf mice, which
    have a low spontaneous rate of such tumours.

         Carcinogenicity studies of both benomyl and carbendazim in rats
    were negative.

    1.1.6.8  Mechanism of toxicity - mode of action

         The biological effects of benomyl and carbendazim result from
    their interaction with cell microtubules. These structures are
    involved in vital functions such as cell division, which is
    inhibited by benomyl and carbendazim. Benomyl and carbendazim
    toxicities in mammals are linked to microtubular dysfunction.

         Benomyl and carbendazim, as well as other benzimidazole
    compounds, display species-selective toxicity. This selectivity is,
    at least in part, explained by the different binding of benomyl and
    carbendazim to tubulins of target and non-target species.

    1.1.7  Effects on humans

         No adverse effects on human health have been reported.

    1.1.8  Effects on other organisms in the laboratory and field

         Carbendazim has little effect on soil microbial activity at
    recommended application rates. Some adverse effects have been
    reported for groups of fungi.

         The 72-h EC50, based on total growth, for the green alga
     Selenastrum capricornutum was calculated to be 1.3 mg/litre; the
    NOEC was 0.5 mg/litre. The toxicity of carbendazim to aquatic
    invertebrates and fish varies widely, with 96-h LC50 values
    ranging from 0.007 mg/litre for the channel catfish to 5.5 mg/litre
    for the bluegill sunfish. In a 21-day test on  Daphnia magna the
    onset of reproduction was significantly delayed at 0.025 mg/litre;
    the NOEC was 0.013 mg/litre.

         Carbendazim is toxic to earthworms in laboratory experiments at
    realistic exposure concentrations and from recommended use in the
    field. It is "relatively non-toxic" to honey-bees and of low
    toxicity to birds.

    1.2  Conclusions

         Benomyl causes dermal sensitization in humans. Benomyl and
    carbendazim represent a very low risk for acute poisoning in humans.
    Given the current exposures and the low rate of dermal absorption of
    benomyl and carbendazim, it is unlikely that they would cause
    systemic toxicity effects either in the general population or in
    occupationally exposed subjects. These conclusions are drawn from
    animal data and the limited human data, but these extrapolations are
    supported by the understanding of the mode of action of carbendazim
    and benomyl in both target and non-target species.

         Further elucidation of the mechanism of toxicity of carbendazim
    and benomyl in mammals will perhaps enable a better definition of
    no-observed-effect levels. Binding studies on tubulins of target
    cells (testis and embryonic tissues) will facilitate inter-species
    comparisons.

         Carbendazim is strongly adsorbed to soil organic matter and
    persists in soil for up to 3 years. It also persists on leaf
    surfaces and, therefore, in leaf litter. Earthworms have been shown
    to be adversely affected (population and reproductive effects) at
    recommended application rates. There is no information on other soil
    or litter arthropods that would be similarly exposed.

         The high toxicity to aquatic organisms in laboratory tests is
    unlikely to be seen in the field because of the low bioavailability
    of sediment-bound residues of carbendazim. However, no information
    is available on sediment-living species, which would receive the
    highest exposure.

    2.  IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND ANALYTICAL METHODS

    2.1  Identity

    2.1.1  Primary constituent

    Common name:             Carbendazim (BSI, ISO)

    Chemical structure:

    CHEMICAL STRUCTURE 1

    Empirical formula:       C9H9N3O2

    Relative molecular mass: 191.2

    CAS chemical name:       Methyl (1H-benzimidazol-2-yl)carbamate

    IUPAC chemical name:     Methyl benzimidazole-2-ylcarbamate

    CAS Registry number:     10605-21-7

    Synonyms:                carbendazol (ZMAF), methyl-2-benzimidazole
                             carbamate (MBC, MCB, BCM, BMC)

    2.1.2  Technical product

         Major trade names:

         Carbendazim, Delsene, Bavistin, Corbel, Konker, Bendazim,
         Derosal, Kombat, Kemdazin, Carbendor, Hoe 017411, Cekudazim,
         Equitdazin, Aimcozim (Some of these are formulations with other
         pesticides.)

    Purity:                  > 98% (FAO specifications)

    Impurities:              2,3-diaminophenazine (DAP), 2-amino-3-
                             hydroxyphenazine (HAP)

    2.2  Physical and chemical properties

    Table 1.  Some physical and chemical properties of carbendazim
                                                                       

    Physical state           Crystalline solid

    Colour                   White

    Odour                    Negligible

    Table 1 (contd).
                                                                       

    Melting point/boiling
    point/flash point        Melts at -250 °C

    Explosion limits         LEL = 0.13 g/litre in air

    Vapour pressure          < 1 x 10-7 Pa (< 1 x 10-9 mbar) at 20 °C

    Density                  0.27 g/cm3 (loose); 0.62 g/cm3 (packed)

    Log  n-octanol/water     1.49
    partition coefficient

    Solubility in water      pH 4      28 mg/litre
    (at 20 °C)               pH 7       8 mg/litre
                             pH 8       7 mg/litre

    Solubility in organic solvents

                             Hexane              0.5 mg/litre
                             Benzene              36 mg/litre
                             Dichlorom ethane     68 mg/litre
                             Ethanol             300 mg/litre
                             Dimethylformamide  5000 mg/litre
                             Acetone             300 mg/litre
                             Chloroform          100 mg/litre

    Henry's constant         1.02 x 10-9 atm-m3/mol at 20 °C
                                                                       

    2.3 Analytical methods

         Methods for determining carbendazim and its by-product residues
    in plant and animal tissue and in soil involve isolation of the
    residue by extraction with an organic solvent and purification of
    the extract by a liquid-liquid partitioning procedure. Measurement
    of the residues may be determined by procedures using high-speed
    cation exchange liquid chromatography, reversed phase HPLC, and
    immunoassay. Recoveries of carbendazim and 2-aminobenzimidazole
    (2-AB) from various types of soils average 88 and 71%, respectively.
    The lower limit of sensitivity of the method is 0.05 ppm for each of
    these components. The recoveries and sensitivities in the case of
    plant tissues are similar. Table 2 outlines various methods for
    soil, water, plants and animal tissue.


    
    Table 2.  Analytical methods for carbendazim
                                                                                                                                          
    Analytical method                  Medium         Detection limit        Comments                               Reference
                                                                                                                                          
    Strong cation exchange/HPLC        soil           0.05 mg/kg             acidic methanol extraction converts    Kirkland et al. (1973)
                                                                             residual benomyl to carbendazim

    Strong cation exchange/HPLC        plant          0.05 mg/kg             acidic methanol extraction converts    Kirkland et al. (1973)
                                                                             residual benomyl to carbendazim

    Strong cation exchange/HPLC        animal         0.01 mg/kg (milk)      acidic aqueous hydrolysis followed     Kirkland (1973)
                                                      0.05 mg/kg             by organic extraction converts
                                                      (tissue)               benomyl to carbendazim and frees
                                                                             metabolites from conjugates

    Reversed phase HPLC                water          9.0 x 10-6 g/litre     on-line HPLC with preconcentration;    Marvin et al. (1991)
                                                                             benomyl and carbendazim
                                                                             determined separately

    Reversed phase                     blueberries    0.03 mg/kg             acidic methanol extraction converts    Bushway et al. (1991)
    HPLC/fluorescence detection                                              residual benomyl to carbendazim

    Radioimmunoassay                   plant          0.05-1.0 mg/kg         ethyl acetate extraction converts      Newsome & Shields
                                                      (dependent on crop)    residual benomyl to carbendazim        (1981)

    Enzyme-linked immunosorbent        plant          0.50 mg/kg             ethyl acetate extraction converts      Newsome & Collins
    assay (ELISA)                                                            residual benomyl to carbendazim        (1987)
                                                                                                                                          
    
    3.  SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE

    3.1  Natural occurrence

         Carbendazim does not occur naturally.

    3.2  Anthropogenic sources

    3.2.1  Uses

         Carbendazim is a fungicide in its own right as well being as
    the main metabolite of other fungicides such as benomyl and
    thiophanate-methyl.

         Carbendazim is used to control a wide range of fungi, including
    Ascomycetes, Fungi Imperfecti and numerous Basidiomycetes, which
    result in plant diseases such as: leaf spots, blotches and blights;
    fruit spots and rots; sooty molds; scabs; bulb, corn and tuber
    decays; blossom blights; powdery mildews; certain rusts; and common
    soilborne crown and root rots. It is used on cereals, cotton,
    grapes, bananas and other fruit, ornamentals, plantation crops,
    sugar beet, soybeans, tobacco, turf, vegetables, mushrooms, and many
    other crops under most climatic conditions worldwide. Registered
    carbendazim usage specifies rates from 0.2 to 2.0 kg a.i./ha and
    applications from once per year to spray intervals ranging from 7 to
    14 days (FAO/WHO, 1985b; 1988b).

         A key limitation to the use of carbendazim and other
    benzimidazoles is the development of fungal resistance. Resistance
    management can be achieved by using carbendazim in combination as a
    tank mix or alternately with other non-benzimidazole fungicides
    (Delp, 1980; Staub & Sozzi, 1984).

         Carbendazim is formulated as an aqueous dispersion, aqueous
    suspension, flowable water dispersible granules and a wettable
    powder.

         In 1991, the estimated worldwide sales of benomyl was US$ 290
    million. This was about 50% of the worldwide market for
    benzimidazole products. Carbendazim (20%) and thiophanatemethyl
    (20%) account for most of the rest of the benzimidazole market
    (County NatWest Woodmac, 1992).

    4.  ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION

    4.1  Transport and distribution between media

    4.1.1  Air

         Carbendazim has a vapour pressure of < 1 x 10-7 Pa (< 1 x
    10-9 mbar) at 20 °C, an aqueous solubility of 8 mg/litre at 20 °C
    and pH 7, and a Henry's constant of approx. 1.02 x 10-9
    atm-m3/mol at 20 °C. It is essentially non-volatile from water
    surfaces.

    4.1.2  Water

         Anaerobic aquatic degradation studies of [phenyl(U)-14C]-
    benomyl in pond water and sediment showed that more than 98% of the
    carbendazim residues partitioned into the sediment after 7 days. The
    half-life of carbendazim was 743 days. After one year 36% of the
    applied radioactivity was bound to the sediment (Arthur et al.,
    1989a).

         An aerobic aquatic degradation study of [phenyl(U)-14C]-
    benomyl in pond water and sediment showed that carbendazim had a
    half-life of 61 days under nonsterile conditions. After 30 days, 22%
    of the applied radioactivity was bound to the sediments and < 1% of
    the applied radioactivity was evolved as carbon dioxide (Arthur et
    al., 1989b).

    4.1.3  Soil

         In greenhouse studies to determine run-off and leaching of
    [2-14C]-carbendazim on soil, a container of Keyport silt loam was
    treated with labelled carbendazim, at a rate of 11 kg a.i./ha, by
    spraying the upper one-third (0.093 m2) of the plot and was
    allowed to stand for 24 h. Artificial rain was then applied (3.75 cm
    the first day after treatment and 2.5 cm on the third and seventh
    days). All water that ran off or leached through the soil was
    collected and analysed for total 14C. Soil in the plot was divided
    into layers for analysis, air dried and analysed separately for
    total 14C. After each of the three rain applications, 0.05-0.39%
    of the applied 14C was found in run-off water; < 0.01% was found
    in the leach water after the first two artificial rains and 0.19%
    after the third one. Soil analyses showed that 90.6% of the applied
    activity remained in the treated area and 93.1% in the top 10 cm of
    soil (Rhodes & Long, 1983).

    4.1.4  Leaching

         To evaluate the risk of pollution of ground and drainage water,
    screening models based on adsorption and persistence can be used,
    together with existing analyses of groundwater samples. Gustafson

    (1989) proposed the use of the equation GUS = log T´ (4 - log
    Koc); GUS values < 1.8 = "improbable leachers", GUS values of
    1.8-2.8 = "transition" and GUS values > 2.8 = "probable leachers".
    For benomyl, Kom values of 550, 620, 2100 and 1100 (mean 1093)
    were found in four different soils (Priester, 1985). A Kom of 1093
    is equal to a Koc of 1857 since Koc = Kom x 1.7. The half-life
    of 320 days given by Marsh & Arthur (1989) seems in good agreement
    with field half-lives of 6 to 12 months (Baude et al., 1974).

         When the calculation of the GUS value is based on a Koc of
    1857 and a T0.5 of 320 days, a value of 1.83 is obtained.
    According to this value, benomyl/carbendazim lies between the
    "improbable leachers" and "transition", and, therefore, would not be
    expected to occur in ground water. The adsorption of benomyl and of
    carbendazim is expected to be of the same order of magnitude since
    the Kow values are almost identical (log Kow = 1.49 and 1.36 for
    carbendazim and benomyl, respectively). In groundwater studies in
    the USA (Parsons & Witt, 1988), benomyl was not found in any of 495
    wells tested and carbendazim not in any of 212 wells (detection
    limit not reported).

         In an EEC survey (Fielding, 1992), the presence of carbendazim
    in groundwater in the Netherlands and in Italy was investigated.
    Carbendazim was found in one of two samples from the Netherlands
    (0.1 µg/litre), and the level was above 0.1 µg/litre in 23 of 70
    samples in Italy. Detection of the non-polar DDT and lindane in many
    wells in the Italian study may indicate macropore transport or
    artifacts such as direct pollution of wells.

    4.1.5  Crop uptake

         Various greenhouse and outdoor tests with carbendazim indicate
    that it remains on plant surfaces as the major component of the
    total residue (Baude et al., 1973).

         A greenhouse crop-rotation study was undertaken by application
    of [2-14C]carbendazim to a loamy sand soil, followed by aging
    periods of 30, 120 or 145 days. The crops studied were beets, barley
    and cabbage. Radioactivity did not accumulate in these crops grown
    to maturity in a loamy sand soil treated 30 days earlier (1.1 kg
    a.i./ha) or 120 to 145 days earlier (3.4 kg a.i./ha). Accumulation
    factors, calculated as the ratio of radioactivity in the crop to
    that in the corresponding soil, were very low in beet foliage (0.04)
    and beet roots (0.03), low in cabbage and barley grain (0.2) and
    ranged from 0.9 to 1.2 in barley straw (Rhodes, 1987).

         Alfalfa, soybean and ryegrass, which were grown in 0.028 m3
    (1 cu ft) containers in a greenhouse in soil treated with an 80:20
    mixture of carbendazim and 2-aminobenzimidazole (2-AB), contained
    small but detectable residues of both compounds. Both 14C-labelled
    and non-labelled mixtures were applied at the rate of 2.2 kg/ha

    uniformly incorporated in the 0-10 cm layer of soil. In the 14C
    studies, alfalfa contained total 14C residues equivalent to
    0.13-0.30 mg/kg of carbendazim/2-AB. Soybean plants contained
    0.32-0.53 mg/kg and ryegrass (20-183 days after planting) contained
    0.09-0.19 mg/kg. Each plant contained approximately equal amounts of
    carbendazim, 2-AB and a polar unknown fraction. Alfalfa from the
    non-labelled series contained 0.05 and 0.08 mg/kg, respectively, of
    carbendazim and 2-AB at the first cutting and < 0.05 mg/kg of each
    compound at the second and third cuttings. Soybean plants contained
    < 0.1 mg 2-AB/kg and 0.59 mg carbendazim/kg. Ryegrass from six
    cuttings (20-149 days after planting) contained 0.08-0.48 mg
    carbendazim/kg and < 0.05 mg 2-AB/kg. All data were calculated on a
    fresh weight basis (Rhodes et al., 1983).

    4.2  Transformation

    4.2.1  Soil biodegradation

         Aerobic degradation studies of labelled [2-14C]-2-AB, the
    primary degradation product of carbendazim in soil, showed that
    14C evolution increased exponentially from 1 to 22 °C, reached a
    maximum at 22 °C, remained almost constant up to 35 °C, then became
    almost zero at 40 °C, when the soil water content was 100% of field
    capacity. At 25 °C, 14C evolution increased exponentially with an
    increase in the field capacity of water from 28 to 94%. These and
    other results indicate the presence of organisms that are able to
    decompose 2-AB (Helweg, 1979).

         Laboratory studies on two types of soil under anaerobic
    conditions using [2-14C]-carbendazim showed only a small amount of
    2-AB (< 0.1%) and no other degradation products (< 0.05%).
    Re-incorporation of 14C into soil humus was indicated by
    fractionation studies, which showed that the unextracted 14C
    residue was widely distributed in various organic soil components
    (Han, 1983b).

         The persistence of carbendazim was monitored in nonsterile and
    sterile Keyport silt loam soil after it was treated with
    [phenyl(U)-14C]-benomyl at a concentration of approximately 7.0
    mg/kg. Distilled water was added to each sample until it reached 75%
    of its moisture-holding capacity at 0.33 bar. The soils were
    incubated in the dark at approximately 25 °C. The nonsterile flasks
    were sampled after 0.1, 0.2, 1, 3, 7, 14, 30, 60, 120, 270 and 365
    days, while samples of sterilized soil were taken after 14, 30, 120,
    270 and 365 days. Carbendazim had a half-life of 320 days under
    nonsterile aerobic conditions (Marsh & Arthur, 1989). This is in
    close agreement with reported half-lives of 6-12 months for
    benzimidazoles applied to bare soil (Baude et al., 1974).

         After 365 days of incubation, 9% of the 14C was evolved as
    14CO2, 34% could still be recovered as carbendazim, and 36% was

    not extractable. The total recovery of 14C was 88%. In the
    sterilized soil, the half-life of carbendazim was approximately 1000
    days (Marsh & Arthur, 1989).

         When the degradation of [2-14C]-carbendazim in soil (20
    mg/kg) was determined, 33% of added 14C was evolved as 14CO2
    during 270 days. Identical or even faster 14C evolution was
    observed from 2-14C-labelled 2-AB (Helweg, 1977). The relatively
    low 14C evolution from phenyl-14C-labelled benomyl/carbendazim
    may be caused by the formation of strongly adsorbed degradation
    products or compounds that are readily incorporated in soil organic
    matter. Thus, most of the remaining radioactivity was accounted for
    in the organic fraction of the soil.

         To elucidate the reason for the low 14C evolution from
    phenyl-14C-labelled fungicide, the fate of a possible degradation
    product, 1,2-diaminobenzene, needs to be determined.

         In a study on the effect of different factors on the
    degradation of carbendazim in soil, carbendazim was found to remain
    in the soil for 120 days. There was 15-29% greater persistence in
    sterilized soil than nonsterilized ones.  Aspergillus niger tiegh.,
     Penicillum chrysogenum Thom.,  Mucor sp and 2 bacteria ( Bacillus
    spp.) alone or in combination degraded the fungicide faster.
    Bacteria were most efficient, and there was faster degradation
    during the first 20 days. High temperature, acidic pH and higher
    moisture level in soil in the presence of microbes all let to faster
    degradation of the fungicide. Soil pre-treatment with microbes
    resulted in rapid degradation (Gupta & Sharma, 1989).

         Soils collected from various fields, which had a history of
    carbendazim application, showed increased carbendazim degradation
    rates. Low initial doses of carbendazim sufficed to condition soil
    with no history of carbendazim application to rapid degradation.
    Previous application of the fungicide was not the only means of
    inducing the phenomenon. When soil with a history of
    carbendazim-treatment was mixed with untreated soil, the ability to
    accelerate degradation was observed in the entire soil volume. This
    capacity was maintained in soil for over 2 years without
    intermediate carbendazim application (Yarden et al., 1987).

         Bean plants grown to maturity in Delaware, USA, contained less
    than 0.1 mg/kg total 14C residue in the edible beans following two
    foliar applications of 1 kg a.i./ha of [2-14C]-carbendazim (as
    Delsene 50% WP) at 25% and 50% bloom. Total 14C residues in the
    bean foliage decreased from about 5 mg/kg one week after the second
    spraying to 0.2 mg/kg three weeks later. The total 14C residue in
    edible beans was less than 0.1 mg/kg one week after the second
    spraying. Of the total 14C in the edible beans and foliage, 89-95%
    was intact free carbendazim and 2-8% was free 2-AB. An additional

    1-3% of the 14C was found as ß-glycosidic conjugates of
    carbendazim and 2-AB (Han, 1983a).

         Chiba & Veres (1981) applied benomyl to apple trees as Benlate
    50% WP at a rate of 1.7 kg/ha. Three successive applications were
    made in 1977 and a single spray was applied in 1979. Between 3 and 7
    days after application there was a marked reduction of about 50% in
    benomyl residues from an initial level of about 110 mg/kg. This fall
    in benomyl was accompanied by a doubling in the level of carbendazim
    residues over the same period due to benomyl degradation to
    carbendazim. Within 46 days of the single appli cation in 1979,
    benomyl residues fell to 0.63 mg/kg foliage and carbendazim was
    present at 1.2 mg/kg. Following the three sprayings in 1977 (at 0,
    13 and 27 days after the initial application), residue levels were
    2.6 and 17.1 mg/kg foliage for benomyl and carbendazim 83 days after
    the first spraying. Both experiments showed an exponential fall in
    benomyl residues but the rate of decline was much slower in the case
    of the more persistent metabolite.

    4.2.2  Abiotic degradation

         The hydrolytic stability of carbendazim at pH 5, 7, and 9 and a
    nominal temperature of 22, 50 and 70 °C was studied at intervals up
    to 30 days. Elevation of temperature and pH increased carbendazim
    degradation. The half-life calculated for the degradation of
    carbendazim at pH 5 and at 22, 50 and 70 °C was 457, 108, and 29
    days, respectively. At pH 7 and at 50 and 70 °C the half-life was 43
    and 12 days (no appreciable decline at 22 °C). The half-life at pH 9
    and at 22, 50, and 70 °C was 22, 1.4 and 0.3 days, respectively
    (Purser, 1987).

         Carbendazim was exposed to sunlight for 30 h (as a residue on
    silica gel G) and less then 10% was lost after exposure.
    Photo-oxidation of the benzene ring of carbendazim was the
    predominant reaction with some guanine, carbomethoxyguanine, and
    carbomethoxyurea detected. When carbendazim was applied to the
    leaves of corn plants and exposed to sunlight for 18 h, no
    photolysis products were detected in the extracts of plants (Fleeker
    & Lacy, 1977).

    4.2.3  Bioaccumulation

         Bluegill sunfish ( Lepomis macrochirus) were exposed to
    radiolabelled carbendazim concentrations of 0.018 or 0.17 mg/litre
    for 4 weeks in a dynamic study designed to measure the
    bioaccumulation of 14C residues in edible tissue, viscera,
    remaining carcass and whole fish. A two-week depuration phase
    followed the exposure phase. Results were similar at the two
    exposure concentrations, the peak whole fish bioconcentration
    factors (BCFs) being 27 and 23 at the low and high exposure levels,
    respectively. The radioactivity was concentrated more in the viscera

    than in other tissues, the peak viscera BCFs being 460 and 380 for
    the low and high exposure levels, respectively. Very little
    bioconcentration occurred in the muscle tissue (BCF = < 4) or the
    remaining carcass (BCF = < 7). During the 14-day depuration phase,
    > 94% of the peak level of radioactivity was lost from the whole
    fish, viscera and muscle. The rate of loss from the carcass tissue
    was lower (77% and 82% loss for the low and high exposure levels,
    respectively) (Hutton et al., 1984).

         When rainbow trout ( Oncorhynchus mykiss), channel catfish
    ( Ictalurus punctatus) and bluegill sunfish ( Lepomis macrochirus)
    were injected intraperitoneally with carbendazim, branchial and
    biliary excretion were the major pathways for the elimination
    (Palawski & Knowles, 1986). In a separate experiment, the three fish
    species were exposed to 45 µg carbendazim/litre for 96 h, except in
    the case of catfish, which were exposed for 48 h. This was followed
    by a 96-h depuration phase. Rainbow trout had the highest uptake
    rate constant (1.78 per h) and bioconcentration factor (159) of the
    three species. Much less carbendazim was accumulated by channel
    catfish than by the other two species, but this residue level (0.44
    µg/g) appeared to be lethal after 48 h of exposure. The elimination
    rate constant and the biological half-life of carbendazim were
    similar for rainbow trout and bluegill sunfish. However, the
    elimination rate constant was greater and the biological half-life
    shorter in channel catfish (13 h) than in the other two species.

    5.  ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE

    5.1  Environmental levels

    5.1.1  Air, water and soil

         The environmental levels in air, water and soil are discussed
    in detail in chapter 4.

    5.1.2  Food and feed

         Levels of carbendazim in food and feed are indicated in section
    5.2.

    5.1.3  Terrestrial and aquatic organisms

         Carbendazim levels in terrestrial and aquatic organisms are
    discussed in detail in chapters 4 and 6.

    5.2  General population exposure

         The principal exposure of the general population to carbendazim
    is through dietary exposure. It was recommended by the Joint FAO/WHO
    Meeting on Pesticide Residues (JMPR) (FAO/WHO, 1985a) that all
    maximum residue limits (MRLs) for benomyl, thiophanate-methyl and
    carbendazim be listed as carbendazim (Tables 3 and 4).

    5.2.1  Sweden

         Monitoring data from Sweden are shown in Table 5 (FAO/WHO,
    1988b). No further analysis to determine dietary intake was
    performed.

    5.2.2  The Netherlands

         Over a period of two years (June 1976 to July 1978), "market
    basket" samples for 16- to 18-year-old males, including 126
    different food items, were purchased every two months. This age
    group was chosen by the authors under the assumption that they had
    the greatest food consumption. The food was prepared for eating
    (including cooking) and combined in 12 different commodity groups,
    and the concentrations of 78 different chemical pesticides were
    determined. Using concentrations found in the total diet samples,
    the daily intakes were calculated. For this sub-population, the
    maximum intake of carbendazim was 0.6 mg/day (calculated using the
    detection limit as the concentration of the non-detectable residues)
    and the average dietary intake was 0.05 mg/day. The recommended ADI
    is 0-0.01 mg/kg body weight (FAO/WHO, 1985a), corresponding to 0.6
    mg/day for a 60-kg adult. Therefore, the maximum intake is at the
    recommended ADI, whereas the average intake is 12 times below the
    recommended ADI (de Vos et al., 1984).


    
    Table 3.  Benomyl/carbendazim/thiophanate-methyl residues in food in Swedena
                                                                                                                                              
    Samples        Swedish/imported    No. of samples    Samples with residues    Residue level    Median value
                                                         >0.20 mg/kg              (mg/kg)          (mg/kg)
                                                                                                                                              

    1986
    Pineapples     imported            3                    1                      0.69

    Grapes         imported            20                   3                      0.17-0.35       0.26

    Strawberries   imported            7                    1                      0.29

    Mangoes        imported            17                   4                      0.20-1.82       0.70

    Papayas        imported            5                    2                      0.25-0.45

    Pears          Swedish             17                   3                      0.32-0.62       0.43
                   imported            45                   7                      0.20-0.45       0.34

    Apples         Swedish             78                   17                     0.20-0.72       0.40
                   imported            91                   30                     0.21-0.74       0.39

    1987
    Grapes         imported            28                   3                      0.52-0.87       0.60

    Strawberries   imported            7                                        0.23

    Mangoes        imported            14                   5                      0.29-1.30       0.66

    Papayas        imported            4                    2                      0.86-1.14
                                                                                                                                              

    Table 3 (contd).
                                                                                                                                              
    Samples        Swedish/imported    No. of samples    Samples with residues    Residue level    Median value
                                                         >0.20 mg/kg              (mg/kg)          (mg/kg)
                                                                                                                                              

    Pears          Swedish             14                   1                      0.52
                   imported            62                   13                     0.21-0.45       0.29

    Apples         Swedish             61                   25                     0.20-1.17       0.45
                   imported            94                   12                     0.21-0.82       0.36
                                                                                                                                              

    a From: FAO/WHO (1988b)

    Table 4.  National Maximum Residue Limits (mg/kg) for certain commoditiesa
                                                                                                                                               
                        banana      cereal      cherries    citrus      bean        cucumber    peach      pome fruit  strawberries   grapes
                                                                                                                                               

    Australia           1           0.05        5           10          3           3           5          5           6              2

    Austria             0.2         0.5                     7           1           0.5                    2           1.5            3

    Belgium             2           0.5         2                       2           0.5         2          5           5              2

    Brazil              1           0.5         10          10          2           0.5         10         5           5              10

    Bulgaria                        0.5         10                                                         5           5              10

    Canada                                      5           10          1           0.5         10         5           5              5

    Denmark             2           0.1         2           5           2           2           2          2           5              5

    France              1                       1.5                                                        6

    Finland             0.2                     1           2           0.5         0.5         1          1           1

    Germany             0.2         0.5         2           7           1           0.5                    2           2              3

    Hungary                                     2                                   1

    Israel                                      10          10                                  10         5                          10

    Italy                           0.5                                                         0.5        1                          1

    Mexico                                                  10          2           11          5          7           5              10

    Netherlands         3           0.1         3           4           3           3           3          3           3              3

    New Zealand         5           1           5           5           2           2           5          5           5              5

    Spain (guidelines)  1           0.5         5           7           2           2           5          5           1              5
                                                                                                                                               

    Table 4 (contd).
                                                                                                                                               
                        banana      cereal      cherries    citrus      bean        cucumber    peach      pome fruit  strawberries   grapes
                                                                                                                                               

    Switzerland         1           0.2         3           7           0.2         0.1         3          3           3              3

    United Kingdom
    (proposed)          1           0.5                     10                      0.5         10         5           5              10

    USA                 1           0.2         15          10          2           1           15         7           5              10

    USSR                1           0.5         10          10          2           0.5         10         5           5              5

    Yugoslavia                      0.1                     7           0.5         0.1                    2           0.5            2
                                                                                                                                               

    a From: FAO/WHO (1988a)
    

    Table 5.  Proposed Maximum Residue Limits for carbendazim from any
              sourcea
                                                                   
    Commodity                     MRL (mg/kg)         Applicationb
                                                                   

    Apricot                       10c                   B,C
    Asparagus                     0.1d                  B,T
    Avocado                       0.5                   B
    Banana                        1c                    B,C,T
    Barley straw and fodder, dry  2                     B
    Bean fodder                   50                    C
    Beans, dry                    2                     B
    Berries and other small fruit 5                     B,C,T
    Brussel sprouts               0.5                   B
    Broad bean                    2                     T
    Carrot                        5c                    C,T
    Cattle meat                   0.1d                  B
    Celery                        2                     B,C
    Cereal grains                 0.5                   B,C,T
    Cherries                      10c                   B,C,T
    Citrus fruits                 10c                   B,C,T
    Coffee beans                  0.1d                  C
    Common beane                  2                     C
    Cucumber                      0.5                   B,C,T
    Eggs (poultry)                0.1d                  B,T
    Egg plant                     0.5                   C
    Gherkin                       2                     C,T
    Hops, dry                     50                    C
    Lettuce, head                 5                     B,C,T
    Mango                         2                     B
    Melons, except watermelons    2c                    B,C
    Milk                          0.1d                  B
    Mushrooms                     1                     B,C,T
    Nectarine                     2                     B
    Onion, bulb                   2                     C,T
    Peach                         10c                   B,C,T
    Peanut                        0.1d                  B,C
    Peanut fodder                 5                     B,C
    Peppers                       5                     C
    Pineapple                     20c                   B
    Plums (including prunes)      2c                    B,C,T
    Pome fruit                    5c                    B,C,T
    Potato                        3c,f                  B,C
    Poultry meat                  0.1d                  B,T
    Rape seed                     0.05d                 C
    Rice straw and fodder, dry    15                    B,C,T
    Sheep meat                    0.1d                  B
    Soya bean, dry                0.2                   C
    Soya bean fodder              0.1d                  C
                                                                   

    Table 5 (contd).
                                                                   
    Commodity                     MRL (mg/kg)         Applicationb
                                                                   

    Squash, summer                0.5                   B
    Sugar beet                    0.1d                  B,C,T
    Sugar beet leaves on tops     10                    B,C,T
    Swedeg                        0.1d                  C
    Sweet potato                  1                     B
    Taro                          0.1d                  B
    Tomato                        5                     B,C,T
    Tree nuts                     0.1d                  B
    Wheat straw and fodder, dry   5                     B
    Winter squash                 0.5                   B
                                                                   

    a From: FAO/WHO (1988b)
    b B = benomyl; C = carbendazim; T = thiophanate-methyl
    c MRL based on post-harvest use
    d At or about the limit of detection
    e JMPR recommended 2 mg/kg for dry, dwarf, lima and snap beans.
      These are all covered by "VP 0526, Common bean" and "VP 0071,
      Beans, dry" in the new classification
    f washed before analysis
    g Described as rutabagas in 1983 recommendation

    5.2.3  National maximum residue limits

         National MRLs for certain commodities are listed in Table 4
    (FAO/WHO, 1988a).

         A complete list of MRLs for carbendazim, including new
    proposals and an indication of the source of the data (application
    of benomyl, carbendazim, or thiophanate-methyl) on which the MRL is
    based, is given in Table 5 (FAO/WHO, 1988b).

    5.3  Occupational exposure during manufacture, formulation, or use

    5.3.1  Exposure during manufacture

         Levels of carbendazim, monitored as worker inhalation exposure,
    in a major manufacturing facility (Du Pont) were reviewed from 1986
    to 1989. The average level of carbendazim was less than 0.3 mg/m3.
    Table 6 lists established inhalation exposure limits for benomyl and
    carbendazim.

    5.3.2  Exposure during use

         Although no studies have been performed with carbendazim,
    potential dermal and respiratory exposure to benomyl wettable powder
    formulation in actual-use situations was determined for tank loading
    and mixing for aerial application, re-entry into treated crops, and
    home use (garden, ornamental and greenhouse). For crop treatments,
    approximately 17 kg benomyl (formulation) was handled per cycle.
    Maximum exposure occurred in the loading and mixing operation for
    aerial application, where dermal exposure was 26 mg benomyl per
    mixing cycle, primarily to hands and forearms (90%), and respiratory
    exposure averaged 0.08 mg benomyl. Re-entry data revealed dermal and
    respiratory exposures of 5.9 mg/h and < 0.002 mg/h, respectively.
    Home-use situations (application of 7 to 8 litres benomyl in
    hand-held compressed air sprayers) produced exposures of 1 mg and
    0.003 mg per application cycle for the dermal and respiratory
    routes, respectively (Everhart & Holt 1982).

    Table 6.  Established inhalation exposure limitsa
                                                                       
    Country and agency   Compound      TWAb                 STELc
                                       (mg/m3)             (mg/m3)
                                                                       
    Australia            benomyl       10                  -

    Belgium              benomyl       10                  -

    Denmark              benomyl       5                   -

    Finland              benomyl       10                  30

    France               benomyl       10                  -

    Switzerland          benomyl       10                  -

    United Kingdom       benomyl       10                  15

    USA: ACGIHd          benomyl       10                  -

    USA: NIOSHe/OSHAf    benomyl       10                  -
                                       (inhalable dust)

    USA: NIOSH/OSHA      benomyl       5                   -
                                       (respirable dust)

    USSR                 carbendazim   -                   0.1
                                                                       

    a From: ILO (1991)
    b Time-weighted average
    c Short-term exposure limit
    d American Conference of Governmental Industrial Hygienists
    e National Institute of Occupational Safety and Health
    f Occupational Safety and Health Administration

    6.  KINETICS AND METABOLISM

         Carbendazim is extensively metabolized by animals as described
    in detail in section 6.3. Metabolite names and structures are given
    in Table 7, Fig. 1 and Fig. 2.

    6.1  Absorption

         Male albino rats were orally administered a single
    14C-carbendazim dose of 12 mg/kg as a solution in diethyl
    glycol-ethanol. Based on urinary excretion of 14C-carbendazim and
    its metabolites, 5-HBC and 2-AB, the absorption was determined to be
    about 85% (Krechniak & Klosowska, 1986).

         In a study by Monson (1990), young male and female
    Sprague-Dawley rats were administered a single dose via gavage with
    14C-radiolabelled [phenyl(U)-14C]-carbendazim (94% pure,
    suspended in corn oil) at either a low (50 mg/kg) or a high (1000
    mg/kg) dose, and excretion of the radiolabel was monitored every 12
    h for 72 h. Most of the radioactivity was excreted by 72 h. The
    percentages of originally administered radioactivity (i.e.
    14C-carbendazim equivalent) recovered were: a) in urine, 61.7
    (male), 53.8 (female) for low dose, 41.4 (male) and 40.7 (female)
    for high dose; and b) in faeces, 24.4 (male), 33.2 (female) for low
    dose and 61.9 (male) and 69.5 (female) for high dose. The author
    concluded that: a) > 98% of the administered dose was recovered in
    urine and faeces in all test groups; and b) the absorption
    efficiency of carbendazim was approximately 80% of the actual
    administered dose for all dose levels, based on the level of
    radioactivity appearing in urine and the sum of all metabolites
    appearing in faeces as the result of hepatic metabolism (Monson,
    1990).

    6.2  Distribution and accumulation

         In a rat gavage study, [phenyl(U)-14C]-carbendazim was
    administered to Sprague-Dawley rats (five rats per sex per group)
    using three dosing regimes: a single oral dose of 50 mg/kg; a single
    oral dose of 50 mg/kg following pre-conditioning gavage of
    non-labelled carbendazim (50 mg/kg) for 14 days; and a single oral
    dose of 1000 mg/kg. All rats were sacrificed 72 h after the last
    dose. Tissue distribution data showed lack of bioconcentration of
    radiolabelled compound. The highest concentrations of radio labelled
    tissue residues (less than 1% of the dose) were detected in the
    residual carcass and liver (Monson, 1990). This study is discussed
    in detail in sections 6.3 and 6.4.

        Table 7.  Carbendazim and its metabolites in animalsa
                                                                             
    Code name           Chemical name
                                                                             

    Carbendazim (MBC)    methyl (1-H-benzimidazol-2-yl)carbamate

    5-HBC                methyl (5-hydroxy-1H-benzimidazol-2-yl)
                         carbamate

    4-HBC                methyl (4-hydroxy-1H-benzimidazol-2-yl)
                         carbamate

    5-HBC-Sb            2-[(methoxycarbonyl)amino]-1H-benzimidazol-5-
                         yl hydrogen sulfate

    5-HBC-Gc            2-[(methoxycarbonyl)amino]-1H-benzimidazol-
                         5-yl] ß-D-glucopyranosiduronic acid

    MBC-4,5-epoxide

    MBC-5,6-epoxide

    MBC-4,5-dihydrodiol  (4,5-dihydro-4,5-dihydroxy-1H-benzimidazol-
                         2-yl) carbamate

    MBC-5,6-dihydrodiol  (5,6-dihydro-5,6-dihydroxy-1H-benzimidazol-
                         2-yl) carbamate

    MBC-4,5-diol

    MBC-5,6-diol

    5-OH-6-GS-MBCd      S-[5,6-dihydro-5-hydroxy-2-(methoxycarbonyl
                         amino)-1H-benzimidazol-4-yl]glutathione

    5-OH-4-GS-MBC        S-[4,5-dihydro-5-hydroxy-2-(methoxycarbonyl
                         amino)-1H-benzimidazol-4-yl]glutathione

    5,6-HOBC-N-oxide     methyl (6-hydroxy-5-oxo-5H-benzimidazol-2-
                         yl)-carbamate-N-oxide

    5,6-HOBC-N-oxide-G   2-[(methoxycarbonyl)amino]-6-oxo-6H-
                         benzimidazol-5-yl] ß-D-glucopyranosiduronic
                         acid-N-oxide

    5,6-DHBC             methyl (5,6-dihydroxy-1H-benzimidazol-2-yl)
                         carbamate
                                                                             

    Table 7 (contd).
                                                                             
    Code name           Chemical name
                                                                             

    5,6-DHBC-G           6-hydroxy-2-[(methoxycarbonyl)amino]-1H-
                         benzimidazol-5-yl] ß-D-glucopyranosiduronic
                         acid

    5,6-DHBC-S           6-hydroxy-2-[(methoxycarbonyl)amino]-1H-
                         benzimidazol-5-yl 5-(hydrogen sulfate)

    2-AB                 2-aminobenzimidazole

    2-AB dihydrodiol     2-amino-4,5-dihydro-4,5-dihydroxy-1H-
                         benzimidazol

    5-HAB                5-hydroxy-2-aminobenzimidazole
                                                                             

    a From: Krechniak & Klosowska (1986); Monson (1986, 1990)
    b S = conjugate with sulfuric acid
    c G = conjugate with glucuronic acid
    d GS = conjugate with glutathione
    
         In a study by Krechniak & Klosowska (1986), male albino rats
    were administered by gavage a single dose of 12 mg carbendazim per
    kg and the distribution of carbendazim and its metabolites among
    subcellular liver fractions was determined 1.5 h after dosing. The
    distribution was not uniform and was not dependent on the lipid
    content of the fractions. The highest relative concentration of
    unchanged carbendazim was in the mitochondria. The highest relative
    concentration of 5-HBC was in the cytosol and that of 2-AB was in
    the microsomes.

         Ten hens were individually dosed for six consecutive days with
    0.625 mg [2-14C]-carbendazim at a rate equivalent to 5 mg/kg in
    the average total daily feed. An additional 10 hens were dosed daily
    with 12.5 mg at a rate equivalent to 120 mg/kg in the average total
    daily feed. The hens were sacrificed 24 h after the sixth dose and
    muscle, kidney, liver and fat were sampled. Carbendazim was
    extensively metabolized to 5-HBC and methyl (4,5-dihydro-4,5-
    dihydroxy-1H-benzimidazol-2-yl) carbamate. The concentration of
    radioactivity, calculated as mg carbendazim per kg, in the high-dose
    hens was 2.63 (liver), 1.74 (kidney), 0.06 (thigh muscle), 0.05
    (breast muscle), 0.03 (fat) and 0.63 (day-6 eggs). Approximately 73%
    of the total radioactivity in the day-6 eggs was identified as 5-HBC
    (0.26 mg/kg) and unchanged carbendazim (0.15 mg/kg) (Monson, 1986).

         In another feeding study, groups of 20 hens were fed
    carbendazim daily at levels of 0, 5, 15 and 100 mg/kg diet for 28
    days. Eggs were collected daily and faeces once a week. After 28
    days, 15 hens in each group were sacrificed and samples taken for
    analysis. The remaining hens were fed a carbendazim-free diet for a
    further week and then sacrificed. The majority of the material fed
    was rapidly eliminated as parent compound or as 5-HBC. The only
    residues found in any of the samples of blood, fat, liver, kidney,
    tissue or eggs were in the eggs from the 100-mg/kg group. However,
    the residues (up to 0.1 mg carbendazim/kg and 0.36 mg 5-HBC/kg each)
    decreased to < 0.05 mg/kg within 4 days of withdrawal of treatment
    (Eckert et al., 1985).

         A lactating Holstein cow was dosed by capsule twice daily (483
    mg [2-14C]-carbendazim each dose), equivalent to 50 mg/kg in the
    average total daily feed, for five consecutive days. Samples of milk
    were collected at each dosing. Approximately 17 h after the tenth
    dose, the cow was sacrificed. Small amounts of radioactivity
    corresponding to carbendazim or its metabolites were found in the
    liver (2.62 mg/kg) and kidney (0.45 mg/kg), but no significant
    amounts (< 0.09 mg/kg) were detected in other tissues or fat. Only
    2.7% of the liver radioactivity was 5-HBC whereas 41% and 3% of the
    kidney radioactivity corresponded to 5-HBC and 4-HBC, respectively.
    14C residue levels in the milk averaged 0.25 mg/kg (calculated as
    carbendazim) of which 0.11 mg/kg was 5-HBC and 0.05 mg/kg 4-HBC. No
    carbendazim (< 0.01 mg/kg) was detected in the milk (Monson, 1985).

         Twelve non-lactating female goats were administered a
    feed-rate-equivalent [phenyl(U)-14C]-carbendazim dose of at least
    50 mg/kg (range: 50-101 mg/kg) once a day for up to 30 days. A
    plateau of 14C residues in the liver was achieved within 2 weeks
    of dose initiation and was calculated to be 9.48 mg/kg of liver
    (group mean of the total radiolabelled liver residues for goats
    sacrificed 2, 3 and 4 weeks after initiation of dosing). The total
    14C residue levels in the liver decreased to 5.17, 3.55 and 1.67
    mg/kg at 1, 2 and 3 weeks, respectively, after discontinuing dosing.
    Based on this data, the elimination half-life for the total 14C
    residues from the liver was calculated to be approximately 9 days.
    The half-life for removal of carbendazim from the general
    circulation, based on 14C-carbendazim equivalent whole blood
    levels, was approximately 10 h. The results of this study suggest
    that levels of carbendazim-derived residues do not continue to
    accumulate beyond 2 weeks when goats are exposed to a constant
    feed-level of 50 mg carbendazim/kg. Furthermore, discontinuation of
    exposure results in a clearing of residues from the liver (Johnson,
    1988).

    6.3  Metabolic transformation

         In a rat gavage study, carbendazim was found to be extensively
    metabolized. Three dosing regimes (five rats of each sex per group)
    were used: a single oral dose of 50 mg/kg (low dose); a single oral
    dose of 50 mg/kg following pre-conditioning gavage with
    non-radiolabelled carbendazim of 50 mg/kg for 14 days
    (pre-conditioned low dose); and a single oral dose of 1000 mg/kg
    (high dose). The 48-h urine from the low-dose and the high-dose
    rats, and the 14-day urine from the pre-conditioned low-dose group
    were collected. The total recovery from urine was 61.5 and 61.7% of
    given doses for the low-dose and pre-conditioned low-dose male
    groups, 53.2 and 59.3% for the low-dose and pre-conditioned low-dose
    female groups, and 39 and 41% for both male and female high-dose
    groups, respectively. 5-HBC-S (21-43% of given dose) was identified
    as the main metabolite, except in the case of the pre-conditioned
    low-dose and the high-dose female rat groups (5.5-10%), while in all
    female rat groups 5,6-HOBC-N-oxide-G (10-19%) was predominant. Both
    5,6-DHBC-S and 5,6-DHBC-G were identified as minor metabolites.

         In the same study, the faeces were collected at the same
    periods as the urine. The total recovery from faeces was about 24%
    for the low-dose and pre-conditioned low-dose male groups, 33-38%
    for the low-dose and pre-conditioned low-dose female groups, and
    higher (> 60%) for both male and female high-dose groups. Unchanged
    carbendazim was about 10-15% of the given dose in the faeces of
    high-dose rats (Monson, 1990). The proposed metabolic pathway for
    carbendazim in rats is given in Fig. 1.

         NMRI mice and Wistar rats of both sexes were given carbendazim,
    via gavage, as a single dose of 3 and 300 mg/kg, respectively. Urine
    was collected during the first 6 h, after which the animals were
    killed. Almost all the metabolites in urine were conjugated with
    sulfuric acid. Cleavage of these conjugates by ß-glucuronidase/
    arylsulfatase released 5-HBC as the only metabolite extractable from
    water. Mouse urine contained a greater amount of compounds that
    remained polar after enzyme treatment than the corresponding urine
    of rats. Analyses revealed no sex differences (Dorn et al., 1983).

         In a further study, male albino rats were administered a single
    intravenous dose of 12 mg carbendazim/kg as a solution in
    diethylene-glycol. The composition of the measured radioactivity in
    urine 12 h after dosing was 94% as 5-HBC, 3% as 2-AB, and 3% as
    carbendazim (Krechniak & Klosowska, 1986).

         In hens dosed with [2-14C]-carbendazim (5 and 120 mg/kg in
    the daily feed), carbendazim was metabolized to 5-HBC, 4-HBC,
    4,5-dihydrodiol-MBC and its sulfuric acid conjugate, and also to
    2-AB (Monson, 1986). The proposed metabolic pathway in laying hens
    is given in Fig. 2.

    FIGURE 1

    FIGURE 2

         The metabolic fate of carbendazim in the liver was examined in
    non-lactating female goats administered a feed-rate-equivalent
    [phenyl(U)-14C]-carbendazim dose of 50 mg/kg once a day for 30
    days. Extraction of liver homogenate from goats sacrificed 4 weeks
    after initiation of dosing, i.e. when the 14C residues in the
    liver had reached a plateau, indicated that the major
    ethyl-acetate-extractable and identifiable radiolabelled residues in
    the liver were 5-HBC (2 to 3 mg/kg) and carbendazim (approximately
    0.2 mg/kg). Bound non-extractable 14C residues in the liver
    reached a plateau level of approximately 1 mg/kg (Johnson, 1988).

         Monson (1991) analysed, via Raney nickel desulfurization and
    acid dehydration, the release and characterization of bound
    carbendazim metabolites in diary cow, goat, hen and rat liver after
    treatment with 14C-carbendazim. Using this technique, he was able
    to show that bound 14C residue was released from the liver of cows
    (76% bound before desulfurization and 36% bound after
    desulfurization) and hens (58% bound before desulfurization and 19%
    bound after desulfurization). The major part of the reduced residue
    was identified as 5-HBC, 5,6-HOBC or carbendazim, suggesting that
    the bound liver residue consisted of conjugates of
    benzimidazole-related products and not natural products resulting
    from breakdown and incorporation.

         Benomyl and carbendazim are metabolized in fish to 5-HBC (Du
    Pont, 1972).

    6.4  Elimination and excretion

         Carbendazim is rapidly excreted in the urine and faeces.

         In a rat gavage study (Monson, 1990), [phenyl(U)-14C]-
    carbendazim was administered to Sprague-Dawley rats using three
    dosing regimes: a single oral dose of 50 mg/kg (low dose); a single
    oral dose of 50 mg/kg following pre-conditioning gavage with
    unlabelled carbendazim of 50 mg/kg for 14 days (pre-conditioned low
    dose); and a single oral dose of 1000 mg/kg (high dose). Each dosing
    group comprised five animals of each sex. A preliminary study
    conducted with two rats of each sex, each rat having received a
    single oral dose of 50 mg/kg, demonstrated that 95% of the
    radioactivity excreted in the urine and faeces was recovered within
    72 h after dosing and that < 1% of the dose was expired as volatile
    metabolites. In the full study, > 98% of the recovered
    radioactivity was excreted by the time of sacrifice (i.e. 72 h after
    dosing) in the case of each group of rats. Urinary excretion
    accounted for 62% to 66% of the dose in males and 54% to 62% of the
    dose in low-dose and pre-conditioned low-dose females. In the
    high-dose group, this pathway accounted for 41% of the dose in all
    animals. Elimination of radiolabel in faeces accounted for virtually
    all of the remaining radiolabel.

         A lactating Holstein cow was dosed by capsule twice daily (483
    mg [2-14C]-carbendazim each dose), equivalent to 50 mg/kg in the
    average total daily diet, for five consecutive days, and samples of
    urine, faeces and milk were collected at each dosing. Five days
    after the initial dose, 65% of the radiolabel had been excreted in
    the urine, 21% in the faeces and 0.4% in the milk (a total of
    86.4%). Radioactive residues in the urine comprised 48% 5-HBC and 3%
    polar water-soluble metabolites (Monson, 1985).

         In a further study, lactating Holstein cows were dosed by the
    dietary route with 0, 2, 10 or 50 mg carbendazim/kg diet for 28
    days. The highest levels of carbendazim metabolites in the urine and
    faeces were found in cows fed 50 mg/kg. The highest levels found in
    urine were 12.56 mg 5-HBC/litre and 1.29 mg 4-HBC per litre. In the
    faeces 3.81 mg 5-HBC/kg and 0.99 mg carbendazim/kg were detected
    (but not in the same cow). No carbendazim residues were found in the
    urine (Hughes, 1984).

         Groups of hens were dosed with [2-14C]-carbendazim at a rate
    equivalent to 5 and 120 mg/kg in the average total daily feed for
    six consecutive days and were sacrificed 24 h after the sixth dose.
    At sacrifice, an average of 95% and 92% of the radioactive doses had
    been excreted in the low-dose and high-dose hens, respectively
    (Monson, 1986).

    6.5  Reaction with body components

         In a study by Guengerich (1981), the effects of carbendazim on
    hepatic enzyme induction were studied in male and female Crl-CD
    rats. The treatment groups included animals fed for 28 days with
    diets that contained carbendazim at concentrations of 0, 10, 30,
    100, 300, 1000 or 3000 mg/kg. Microsomal epoxide hydrolase and
    cytosolic glutathione- S-transferase were monitored in subcellular
    fractions isolated from the livers of animals in each treatment
    group. Liver weights were also recorded. Elevated liver weights were
    observed at 1000 and 3000 mg carbendazim/kg in both male and female
    rats. No apparent liver toxicity or effect on body weight was
    observed. Carbendazim induced epoxide hydrolase in both sexes of
    rats and mice at 1000 and 3000 mg/kg. Induction of
    glutathione- S-transferase was observed at 3000 mg/kg. In general,
    the level of induction seemed to be slightly greater in females than
    males.

         In the same study, but in a separate test, CD-1 male mice were
    treated via gavage with carbendazim suspended in corn oil (0, 100
    and 1000 mg/kg per day) for 5 days. The liver samples were
    homogenized and subcellular fractions were prepared as above. Wet
    liver weights, microsomal cytochrome P-450, NADPH-cytochrome-c
    reductase, styrene-7,8-hydrolase, benzphetamine- N-demethylase,
    benzo(a)pyrene hydroxylase and 7-ethoxy coumarin  O-deethylase, and
    cytosolic glutathione- S-transferase were measured. Those

    parameters showing statistically significant increases over the
    control values were styrene-7,8-hydrolase and glutathione- S-
    transferase; 7-ethoxycoumarin  O-deethylase showed a significant
    decrease. It is noteworthy that the total microsomal cytochrome
    P-450 level did not increase, indicating that a whole scale
    microsomal induction phenomena was not induced by carbendazim even
    at the higher treatment level. However, as shown by the increase in
    microsomal styrene-7,8-hydrolase, some hepatic microsomal enzymes
    are induced by  in vivo carbendazim treatment (Guengerich, 1981).
    There did not appear to be any substantial difference in enzyme
    induction between rats and mice.

    7.  EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS

    7.1  Single exposure

         The acute toxicity of carbendazim in several animal species is
    summarized in Table 8. The LD50 values range from > 2000 to > 15
    000 mg/kg for a wide variety of test animals and routes of
    administration. A description of toxic effects is given in section
    7.5.1.

    7.2  Short-term exposure

    7.2.1  Gavage

         Groups of ChR-CD male rats (six per dose level) were gavaged
    with 200, 3400 and 5000 mg carbendazim/kg per day, five times/week,
    for two weeks. Two out of six rats died at the dose level of 3400
    mg/kg per day. At all dose levels, gross and microscopic evidence of
    adverse effects on testes and reduction or absence of sperm in the
    epididymides was seen. Testes were small and discoloured, with
    tubular degeneration and evidence of aspermatogenesis. At the dose
    level of 3400 mg/kg per day, there were also morphological changes
    in the duodenum (oedema and focal necrosis), bone marrow (reduction
    in the blood-forming elements) and liver (decrease in the large
    globular-shaped vacuoles) (Sherman, 1965; Sherman & Krauss, 1966).

         Subchronic administration of 0, 16, 32 or 64 mg carbendazim per
    kg per day by gavage for 90 days to four groups of 10 male and 10
    female litter-mate weaning Wistar rats was carried out. The
    erythrocyte counts for treated rats were lower than those of the
    controls after 15 days of exposure. However, no clear dose-response
    relationship was demonstrated after 30, 60 or 90 days of exposure. A
    decrease was noted in leucocyte counts at 15 days. After 30 and 60
    days, both sexes demonstrated transient decreases in lymphocyte
    counts compared to controls. However, no clear dose-response
    relationship was observed among the treated groups. No change was
    noted in the activity of whole blood cholinesterase. Male rats
    showed significantly increased alkaline phosphatase activity at a
    dose level of 64 mg/kg per day. Blood urea levels were lower in
    males at dose levels of 32 and 64 mg/kg per day after 90 days.
    Increased serum bilirubin concentrations were observed in males and
    females at 32 and 64 mg/kg per day and were attributable to
    parenchymal cell damage, as shown by increased glutamic-pyruvic
    transaminase activity. Dose-related changes in the liver ranged from
    sparse infiltration by inflammatory cells to inflammatory and
    degenerative changes. Tubular dilation and hydropic degeneration
    were noted in the kidneys of the low-dose rats, and fibrosis and
    congestion in the medium- and high-dose rats. Increased lung weight
    was correlated with bronchopneumonic changes. Slight changes in
    weights were reported for several organs (Janardhan et al., 1987).
    The published information was difficult to evaluate due to the
    variability of the results and absence of the raw data.


    
    Table 8.  Acute toxicity of carbendazim in animals
                                                                                                                                     
    Chemical       Species     Sex   Animals   Route             Vehicle               Concentrationa         Reference
                                     per group                                         (mg/kg body weight)
                                                                                                                                     
    Carbendazim    rat         M/F   10        oral              sesame oil            LD50 > 15 000         Kramer & Weigand (1971)
    (MBC)          rat         M     10        intraperitoneal   0.9% saline           LD50 > 2000           Goodman & Sherman (1974)
                                                                 and Tween 80
                   rat         M     6         inhalation (1 h)  dust                  ALC > 5.9 mg/litreb   Sarver (1975)
                   rat         F     5         dermal            sesame oil            ALD > 2000            Kramer & Weigand (1971)
                   mouse       M     10        oral              propylene glycol      LD50 > 15 000         Til & Beems (1981)
                   mouse       M/F   10        intraperitoneal   sesame oil            LD50 > 15 000         Scholz & Weigand (1972)
                   dog         M/F   2         oral              sesame oil            ALD50 > 5000          Scholz & Weigand (1972)
                   guinea-pig  M     10        oral              corn oil              LD50 > 5000           Dashiell (1975)
                   rabbit      M     10        dermal            aqueous paste         LD50 > 10 000         Edwards (1974a)
    75% wettable   rat         M/F   5         oral              corn oil              LD50 > 5000           Hinckle (1981)
    powder
                   rat         M/F   10        inhalation        dust                  LC50 > 5 mg/litre     Nash & Ferenz (1982)
                   rabbit      M/F   5         dermal            physiological saline  LD50 > 2000           Ford (1982)
    Benlate C      rat         M/F   5         oral              water                 LD50 > 5000           Grandizio & Sarver (1987)
    (50% wettable  rabbit      M/F   5         dermal            aqueous paste         LD50 > 2000           Vick & Brock (1987b)
    powder)
                                                                                                                                     

    a ALC = approximate lethal concentration; ALD = approximate lethal dose
    b Time-weighted concentration
    

    7.2.2  Feeding

    7.2.2.1  Rat

         Groups of ChR-CD rats (16 males and 16 females per group) were
    fed carbendazim (72% a.i.) in the diet for 90 days at levels of 0,
    100, 500 and 2500 mg/kg. The animals were observed daily for
    behavioural changes and body weight, and food consumption were
    recorded at weekly intervals. Haematological examinations were
    conducted on 10 male and 10 female rats in each group at 30, 60 and
    90 days. Routine urinalyses were performed on the same animals, and
    plasma alkaline phosphatase and glutamic-pyruvic transaminase levels
    were determined. After 90 to 98 days of continuous feeding, 10 male
    and 10 female rats in each group were killed and selected organs
    weighed. These and other organs were preserved for microscopic
    examination. The six male and six female rats remaining in each
    group after terminal sacrifice were used in a reproduction study
    (see section 7.5.1). There were no signs of poisoning and no
    compound-related effects on weight gain, food consumption or
    haematological parameters. There were no control data for
    biochemical determinations, urinalysis or differential white blood
    counts. The average dose for the high-dose animals was 360 mg/kg per
    day initially and 123-152 mg/kg per day at sacrifice. The
    liver-to-body-weight ratio in females fed 2500 mg/kg diet was
    slightly increased compared with control rats. There were no effects
    on testicular weights in any of the treatment groups. Microscopic
    examination of selected tissues and organs in the control and
    high-dose groups demonstrated no adverse effects attributable to
    carbendazim (Sherman, 1968).

    7.2.2.2  Dog

         Groups of one-year-old beagles (four males and four females per
    group) were administered carbendazim (53% a.i.) in the diet for
    three months at dietary levels of 0, 100, 500 and 2500 mg/kg. The
    highest level was reduced to 1500 mg/kg because of reduced food
    intake and decreased body weight. However, compound administration
    was interrupted when animals were fed a control diet for a few days
    and then fed with 1500 mg/kg again.

         Food consumption and body weight data were recorded weekly, and
    clinical laboratory examinations (including haematological,
    biochemical and urinalysis measurements) were performed pre-test and
    after 1, 2 and 3 months of feeding. At the end of the study all
    animals were killed, selected organs were weighed, and these and
    other organs were subjected to gross and microscopic evaluations.

         No mortality or adverse clinical signs were observed over the
    course of the study, and growth and food consumption were normal
    (except at 1500-2500 mg/kg). Urinalysis measurements were unaffected
    by treatment, and there were no dose-related effects on the
    haematological values. Females at the mid-dose level showed a trend

    toward increased cholesterol levels at 1, 2 and 3 months compared
    with the pre-test and control values. High-dose females had
    similarly elevated cholesterol levels. Organ-to-body weight changes
    were observed in the case of the thymus of low- and mid-dose males
    and the prostate of mid-dose males. All the weights for these organs
    were increased compared with control values. However, only the
    liver, kidney and testes were examined histologically in the low-
    and mid-dose groups. Limited histopathological data did not indicate
    compound-related effects (Sherman, 1970).

         In a study by Til et al. (1972), groups of beagles (four males
    and four females per group) were administered carbendazim in the
    diet at levels of 0, 100, 300 and 1000 mg/kg for 13 weeks. The
    highest level was increased to 2000 mg/kg after six weeks of
    treatment. Body weight, haematological and blood chemistry
    measurements, urinalyses and liver/kidney function tests were
    performed periodically. Gross and microscopic examinations of all
    animals were performed at the end of the study. There were no
    reported compound-related effects on clinical behaviour, body
    weight, food consumption, haematological parameters, kidney function
    (phenol red excretion) or liver function (BSP retention)
    examinations. Blood chemistry measurements were normal, except for a
    slight decrease in albumin in mid- and high-dose males at 12 weeks.
    These values differed from week 0 measurements only in high-dose
    males. Urinalysis values were normal except for a high bacterial
    count in high-dose females at week 13. The blood clotting time was
    slightly reduced in high-dose dogs at week 12. There were slight
    increases in relative liver and thyroid weights and a decrease in
    relative heart weights in the highest-dose group compared with
    controls. No microscopic changes that could be associated with
    treatment were observed in these or any other organs. Carbendazim
    appeared to be without adverse effects on beagles when incorporated
    in the diet for 13 weeks at dietary levels of 300 mg/kg or less.

    7.2.3  Dermal

         New Zealand albino rabbits (six males/group) were treated with
    0 or 2000 mg/kg of carbendazim, applied as a 50% aqueous paste to
    shaved intact dorsal skin. The material was applied repeatedly, 6
    h/day, for ten consecutive days. There were no adverse effects on
    body weight, clinical symptoms, organ weights, gross pathology or
    histopathology of selected organs. However, there was focal necrosis
    of the epidermis and polymorphonuclear cell infiltration of the
    dermis in five out of six exposed rabbits. No other effects were
    observed (Dashiell, 1975).

    7.3  Skin and eye irritation; sensitization

    7.3.1  Dermal

         The primary dermal irritation potential of Benlate C (50%
    wettable powder) was evaluated by applying a 5-g aliquot for 4 h to
    the clipped intact skin of six New Zealand White rabbits. Test sites
    were evaluated for erythema, oedema and other evidence of dermal
    effects, and were scored according to the Draize scale at 4, 24, 48
    and 72 h after application. No dermal irritation was seen at any
    time during the study (Vick & Brock, 1987a).

    7.3.2  Eye

         No eye irritation potential for technical carbendazim was seen
    in six albino rabbits (Edwards, 1974b). In a study by Vick &
    Valentine (1987), a 50% wettable powder (formulation) was evaluated
    for acute eye irritation potential in six male New Zealand white
    rabbits. The formulation produced slight corneal opacity, mild or
    moderate conjunctival redness, and slight or mild conjunctival
    oedema in all the rabbits. In addition, there was moderate iritis in
    three of the rabbits and minimal blood-tinged discharge in one
    rabbit. Microscopic examinations revealed no corneal injury in any
    of the treated eyes. The treated eyes of the two other rabbits were
    normal by 72 h. It was concluded that this formulation was a
    moderate eye irritant.

    7.3.3  Sensitization

         Albino guinea-pigs (10 males) exposed to carbendazim, either
    technical material or a 75% wettable powder formulation, presented
    no evidence of dermal sensitization following either intradermal
    injections or repeat applications to shaved intact skin (Ford,
    1981).

         A 50% carbendazim formulation was tested on the shaved intact
    skin of 10 male and 10 female Duncan Hartley albino guinea-pigs.
    Five male and five female guinea-pigs were treated with 80% ethanol
    (in water) and served as vehicle control animals. Two male and two
    female guinea-pigs were treated with the test material (as a solid)
    at the challenge phase only and served as negative control animals.
    1-Chloro-2,4-dinitrobenzene (DNCB) was tested as a 0.3% suspension
    in 80% ethanol (in water) on the shaved intact skin of two male and
    two female guinea-pigs as a positive control group. No irritation
    was observed in the test or vehicle control guinea-pigs or in the
    negative controls at the challenge phase. DNCB produced
    sensitization in all treated animals (Martin et al., 1987).

    7.4  Long-term exposure

    7.4.1  Rat

         Groups of weanling rats (36 male and 36 female ChR-CD albino
    rats/group) were administered carbendazim (50-70% a.i.) in the diet
    for 104 weeks at levels of 0, 100, 500, 2500 (increased to 10 000
    mg/kg after 20 weeks) and 5000 mg/kg diet. Body weight and food
    consumption were recorded weekly for the first year and twice a
    month thereafter. Daily observations were made with respect to
    behavioural changes and mortality. At periodic intervals throughout
    the study, haematological, urinalysis and selected clinical
    chemistry examinations were performed. After one year each group was
    reduced to 30 male and 30 female rats by interim sacrifice for gross
    and microscopic examinations. At the end of the study all surviving
    animals were sacrificed and gross examination of tissues and organs
    was made. Microscopic examinations were conducted on all tissues and
    organs from the control and 2500-mg/kg groups, the livers of the
    100- and 500-mg/kg groups, and the livers, kidneys, testes and bone
    marrow from the 5000-mg/kg groups. Survival decreased during the
    second year to approximately 50% for males and 39% for females in
    all groups. Body weight gain was depressed for males and females in
    the 2500-mg/kg group and for females in the 5000-mg/kg group,
    compared to control groups. Food consumption did not differ among
    the various groups. The average daily dose for the 500-mg/kg group
    was 65 mg/kg body weight per day initially, 18 mg/kg body weight per
    day at one year, and 15 mg/kg body weight per day at two years.
    Haematological examinations demonstrated reduced erythrocyte count
    and haemoglobin and haematocrit values for females at 9-24 months in
    the 2500- and 5000-mg/kg groups, and for males at 24 months in the
    2500-mg/kg group. There were no compound-related clinical
    manifestations of toxicity and no effects observed in urinalysis
    examination. Alkaline phosphatase and glutamic-pyruvic transaminase
    activity varied throughout the test at 2500 and 5000 mg/kg but did
    not demonstrate a consistent dose-response relationship. There were
    no apparent differences in the organ weights or organ-to-body weight
    measurements, except in the case of female livers in the 2500- and
    5000-mg/kg groups. This increase in the liver-to-body weight ratio
    was due to a reduction in body weight. Histopathological examination
    of the livers did not demonstrate any compound-related effects.
    Males in the 2500-mg/kg group presented a marginal increase in
    diffuse testicular atrophy and prostatitis (Sherman, 1972).

         In another 2-year rat study, groups of Wistar rats (60 males
    and 60 females/group) were administered carbendazim (99% pure) in
    the diet at levels of 0, 150, 300 and 2000 mg/kg diet for two years.
    The dose of 2000 mg/kg was increased to 5000 mg/kg after one week
    and then to 10 000 mg/kg after two weeks for the remainder of the
    study. Animals were examined daily for clinical signs of toxicity.
    Body weight and food consumption were measured regularly throughout
    the study. Haematological (peripheral blood), blood chemistry

    (orbital sinus) and urinalysis evaluations were conducted
    periodically during the study. All animals were subjected to
    complete gross necropsy, and selected organs were weighed. Tissues
    were examined microscopically in 20 male and 20 female rats in the
    control and high-dose groups. All tumours and gross abnormalities
    were also examined histologically. There were no differences between
    test groups and control animals concerning clinical signs of
    toxicity or food consumption. Body weights were significantly
    reduced in low-dose males from week 88 to term and in high-dose
    females from week 12 to term. Urinalyses were comparable among all
    groups. Of the haematological parameters examined, haemoglobin was
    depressed in high-dose females at weeks 26, 52 and 103 and
    haematocrit was depressed in high-dose females at week 103. There
    were no compound-related effects in males. Serum glutamic
    oxaloacetic transaminase (SGOT) activity was decreased in high-dose
    males at term, but not in females. High-dose females had increased
    serum glutamic pyruvic transaminase (SGPT) activity and decreased
    total serum protein at study termination. There were no
    compound-related effects on organ weights except for increased
    relative liver weights in high-dose females. There were also no
    compound-related effects on mortality, this being 50% at week 76 in
    control males and at week 92 in treated males. There was 50%
    mortality in control and low-dose females at week 88 and in mid- and
    high-dose females at 92-96 weeks. Survival at termination of the
    study was similar in all groups.

         There were no histological differences between control and
    treated groups except for an increased incidence of diffuse
    proliferation of parafollicular cells of the thyroid in the
    high-dose females (Til et al., 1976a).

    7.4.2  Dog

         In a one-year study, beagle dogs (five of each sex per group)
    were fed diets containing 0, 100, 200 or 500 mg carbendazim/kg. The
    dogs were weighed at regular intervals, and individual food
    consumption was monitored throughout the study. Clinical pathology
    evaluations were performed twice prior to the initiation of the
    study and five times during the study, at 1, 3, 6, 9 and 12 months.
    After one year, all dogs were killed and selected tissues were
    examined microscopically. There were no statistical differences in
    mean body weight that could be attributed to carbendazim exposure.
    The mean daily food consumption in all treated groups of dogs was
    similar to controls. None of the clinical observations were
    attributable to carbendazim intake. Dogs fed 500 mg/kg had elevated
    levels of serum cholesterol. These levels were statistically
    significant for the males at 9 months and the females at 1 and 2
    months. There were no compound-related microscopic lesions related
    to carbendazim intake (Stadler, 1986).

         Groups of beagles (four males and four females per group) were
    administered carbendazim (53% a.i.) in the diet at dosage levels of
    0, 100, 500 and 2500 mg/kg for two years. The dogs were 1-2 years of
    age at the start of the test. Food consumption and body weight data
    were obtained weekly and animals were examined daily for clinical
    signs of toxicity. Haematological, biochemical and urinalysis
    examinations were performed periodically throughout the study.
    Interim sacrifice after one year was performed on one male and one
    female from the control and 500-mg/kg groups. Organ weight, gross
    necropsy and histopathological examinations were performed at the
    end of the study. Only the livers and testes were examined
    histologically in the 100- and 500-mg/kg groups. No mortality was
    reported for the control or the 100- and 500-mg/kg dose groups. The
    average daily intake for the 500-mg/kg dose group was 15.0-20 mg/kg
    body weight per day initially, 14-18 mg/kg body weight per day after
    one year and 10-16 mg/kg body weight per day after two years.
    Haematological and urinalysis values were unaffected by treatment.
    The dogs in the 500-mg/kg groups had increased levels of
    cholesterol, blood urea nitrogen (BUN), total protein and SGPT.
    Swollen vacuolated hepatic cells and marginal proliferation of the
    portal triads with cellular infiltration was observed in one dog
    sacrificed after one year, which had been fed 500 mg/kg. No
    histopathological liver lesions were observed in animals fed 500
    mg/kg diet at the end of the study. Although inflammatory and
    fibrotic liver changes were observed in the 2500-mg/kg group, these
    changes cannot be evaluated because of the uncertainty of the dosing
    regime, of the time of exposure and of the number of dogs. There
    were no noticeable effects on organ weights or on organ-to-body
    weight ratios. Diffuse testicular atrophy and aspermatogenesis were
    observed in males (two out of four) at 100 mg/kg but not at 500
    mg/kg (Sherman, 1972).

         In another 2-year dog study, groups of beagles (four males and
    four females per group) were fed technical carbendazim in the diet
    at dosage levels of 0, 150, 300 and 2000 mg/kg for 104 weeks. After
    33 weeks the dose 2000 mg/kg was increased to 5000 mg/kg. The dogs
    were 22-27 weeks old at the start of the study. Daily examinations
    were made for clinical signs of poisoning or adverse behaviour. Body
    weight and food consumption data were recorded regularly throughout
    the study. At periodic intervals (weeks 13, 26, 52, 78 and 104),
    haematological, blood chemistry and urinalysis measurements were
    made. Liver function (BSP retention) and kidney function (phenol red
    excretion) tests were conducted at weeks 26, 52 and 104. At the
    conclusion of the 104 weeks of dietary administration, each dog was
    sacrificed and gross and microscopic examination of tissues and
    organs was performed. There was no mortality in any group except for
    one female in the high-dose group which was killed in a moribund
    state after week 36. Body weight was decreased in mid-dose males and
    high-dose males and females. Food consumption was comparable among
    all groups. Blood clotting times were significantly reduced in
    high-dose males from week 13 to term, and slight decreases were
    noted in high-dose females. Serum alkaline phosphatase activity was

    increased in the high-dose group throughout the study. There were no
    compound-related effects on SGPT or SGOT levels. All other
    haematological and blood chemistry values were comparable with
    control groups. There were no differences for BSP retention, phenol
    red excretion or urine analysis values among the various groups.
    Absolute liver and thyroid weights were significantly increased in
    high-dose dogs. Relative liver, thyroid and pituitary weights were
    also significantly increased at the high-dose level. There were no
    reported microscopic changes in these organs related to treatment.
    There was an increased incidence of prostatitis (3/4 versus 1/4) in
    high-dose males compared with controls. Also noted in high-dose
    males (1/4) was interstitial mononuclear inflammatory cell
    infiltrates and atrophic tubules of the testes. It was concluded
    that the feeding of carbendazim in the diet to dogs for two years
    was without apparent adverse effects at levels up to and including
    300 mg/kg (Reuzel et al., 1976).

    7.4.3  Mouse

         A description of studies on mice is given in section 7.7.

    7.5  Reproduction, embryotoxicity and teratogenicity

    7.5.1  Reproduction

         Groups of ChR-CD rats (3 male and 16 female rats per group,
    except that the high-dose group contained 20 females) were fed
    carbendazim in the diet at dose levels of 0, 100, 500, 5000 and 10
    000 mg/kg and subjected to a standard two-litter-per-generation,
    three-generation reproduction study. The parental animals were fed
    the experimental diet at 21 days of age and mated to produce the
    F1 litter at 100 days of age. The number of matings, pregnancies
    and number of young in each litter at birth was recorded. The
    litters were culled to 10 pups/litter on day 4. The number of the
    live pups was recorded on days 4, 12 and 21, as was pup weight at
    weaning. The parents were mated again to produce the F1B litters.
    The F1B litters were maintained on the respective diets for 110
    days and then mated to produce the F2A and F2B litters. The
    F3A and F3B litters were produced similarly. Gross and
    histopathological examinations of selected tissues and organs were
    performed on two males and two females in each of five F3litters
    from the control, 5000- and 10 000-mg/kg groups. Reproduction
    indices, including mating, fecundity, fertility, gestation,
    viability and lactation, were calculated and compared with control
    values. Carbendazim was without effect on fertility, gestation,
    viability and lactation. However, the average litter weights at
    weaning were reduced in all generations fed 5000 and 10 000 mg/kg.
    Histopathological examination of F3B weanlings did not reveal any
    effects that were considered compound-related (Sherman, 1972).

         Two additional feeding studies (Sherman, 1968; Koeter et al.,
    1976) were reviewed by the 1983 Joint FAO/WHO Meeting on Pesticide
    Residues (JMPR), which concluded that both reports had limitations.
    For the Sherman (1968) study, it was stated that the "data presented
    were extremely limited and submitted as group data only. There were
    no pregnancies at 100 mg/kg diet for either F1a or F1b matings.
    There were no apparent effects on the reproduction indices on
    weanling weights. However, the fertility index for all groups, which
    was 33-67% prevents any meaningful interpretation of the data"
    (FAO/WHO, 1985b). For the study of Koeter et al. (1976), the 1983
    JMPR concluded that "although there were no apparent adverse effects
    on reproduction and no teratogenic effects at dietary levels of
    carbendazim up to and including 2000 mg/kg, there were no individual
    animal data presented. Histopathology of animals in the four-week
    study was incomplete and did not include evaluations of spleen or
    ovaries. Such additional data are needed to confirm the absence of
    adverse effects in this three-generation reproduction study in rats"
    (FAO/WHO, 1985b).

         A serial breeding technique was used to evaluate the fertility
    of male Sprague-Dawley rats after exposure by gavage to 10 daily
    doses of carbendazim (400 mg/kg per day). Proven-fertile males (90
    days old) were bred with a new female each week. Breeding began on
    the third day of treatment and continued for 32 weeks after the last
    day of chemical exposure. Twelve days after each breeding period,
    the females were killed, their uteri were examined for resorptions,
    and the number of dead and viable fetuses was determined. All males
    were killed 35 weeks after the exposure, and testicular tissue was
    prepared for histopathological examination by vascular perfusion.
    The fertility (as indicated by the number of pregnant females) of
    males in the carbendazim-treated group was depressed during the
    first post-exposure week; 10 of the 24 treated males failed to
    induce a pregnancy, as compared with no failure in the control
    group. By the fifth post-exposure week, 16 of the 24
    carbendazim-treated males were infertile. Of these 16 males, 4
    recovered fertility after being infertile for 5-11 consecutive
    breeding periods. However, 12 of the males did not recover fertility
    during the remainder of the 32 week post-exposure period.
    Histological examinations of testicular sections 245 days after the
    exposure revealed that the exposure to carbendazim had caused severe
    seminiferous tubular atrophy (> 85% of tubules were atrophic) in
    those treated males that failed to recover fertility. The
    seminiferous tubules of these males often showed "Sertoli cell only"
    syndrome epithelium surrounded by a thickened basement membrane.
    Less than 2% of the tubules contained spermatozoa in the lumen. The
    seminiferous tubules of the carbendazim-treated males that recovered
    fertility had various numbers of atrophic tubules (13-85%) 245 days
    after the exposure (Carter et al., 1987).

         In another study, groups of male and female rats (8-12 of each
    sex per group) were administered 0, 50, 100, 200 or 400 mg
    carbendazim/kg per day by gavage from weaning through puberty,
    gestation and lactation, and they were mated at 84 days of age. The
    male rats were killed on day 104-106 while the female rats were
    killed on day 27 postpartum. A similar study was conducted with
    Syrian hamsters administered 0 or 400 mg/kg per day. In the parental
    generation, various landmarks of puberty were measured. In females,
    estrous cyclicity, litter size, the number of implants, organ
    weights and histological status were assessed. In males, organ
    weights, testicular and epididymal sperm counts, sperm motility,
    sperm morphology, testicular histological status, and endocrine
    parameters were assessed. In addition, the growth, viability and
    reproductive function of the offspring (F1) were observed during a
    4-month period of continuous breeding. Males were killed at 5 months
    for histopathological investigation. In the parental generation of
    both species, carbendazim did not alter pubertal development, growth
    or viability. The reproductive potential of rats treated with
    carbendazim with 200 and 400 mg/kg per day was reduced due to
    effects on sperm production and fetal viability. In the male rat,
    carbendazim treatment with 200 or 400 mg/kg per day markedly altered
    sperm morphology, testicular and epididymal weights, sperm numbers
    and testicular histology. Fertility, sperm motility and hormonal
    levels were altered primarily in those males fed 200 or 400 mg/kg
    per day that exhibited very low sperm counts. A statistically
    significant reduction in caudal epididymal sperm count was noted at
    dose levels of 50 mg/kg per day or more. Testicular and epididymal
    sperm counts in male hamsters were significantly lower (about 21%)
    in the carbendazim-treated males compared with the control males. In
    the F1 male hamsters, testis and seminal vesicle weights and
    epididymal sperm counts were significantly reduced by prenatal
    exposure to carbendazim at 400 mg/kg per day. In the parental female
    rats, carbendazim administration caused postimplantation losses at
    400 mg/kg per day and a few malformed rat pups were found in litters
    at 100 and 200 mg/kg per day. Litter size was significantly reduced
    at 200 and 400 mg/kg per day. Overall, carbendazim was less toxic to
    the hamster than to the rat (Gray et al., 1988, 1990).

         Since spermatogenesis is an androgen-dependent process, the
    effects of carbendazim (0-400 mg/kg per day by gavage) on the
    endocrine function of the rat testes were investigated. Following
    subchronic (85 day) exposure, serum hormone levels, including those
    of pituitary luteinizing hormone (LH), follicle-stimulating hormone
    (FSH), thyroid-stimulating hormone (TSH), prolactin (PRL), and
    androgen-binding protein (ABP) and testosterone in testicular fluids
    (interstitial fluid and seminiferous tubule fluid) were measured. In
    addition, the functional capacity of the Leydig cell to secrete
    testosterone was assessed  in vitro following human chorionic
    gonadotrophin (HCG) challenge. Subchronic treatment with carbendazim
    at doses of 50-100 mg/kg per day had no effect on pituitary or
    testicular hormone concentrations; dosing with 200 mg/kg per day
    elevated the testosterone concentration in the seminiferous tubule

    fluid and the ABP tubule fluid without affecting serum testosterone
    or ABP concentrations. The dose of 400 mg/kg per day resulted in
    increased concentrations of both testosterone and ABP in the
    interstitial fluid and seminiferous tubule fluid and of serum ABP,
    but no change in serum testosterone level. These hormonal changes
    are consistent with carbendazim effects on the gonads and resultant
    testicular atrophy. This endocrine profile is similar to the
    "Sertoli cell only" syndrome discussed by de Krester (1977). Thus,
    the elevated seminiferous tubule fluid testosterone concentrations
    may be a result of two factors: (a) greater release of testosterone
    by the Leydig cells into the interstitial fluid; and/or (b)
    decreased testosterone outflow from the testis into the general
    circulation. In addition, increased ABP in the interstitial fluid
    may reflect a change in the relative secretion of ABP into the
    interstitial fluid and the seminiferous tubules (Rehnberg et al.,
    1989).

         Since it is possible that extragonadal changes contributed to
    the appearance of the altered testicular endocrine profile described
    above, a further study focused on the presence of concurrent changes
    in the hypothalamus and pituitary control of the testes. In this
    study, rats were gavaged with carbendazim (50, 100, 200 or 400 mg/kg
    per day) for 85 days (Gray et al., 1988). A dose-related increase in
    serum FSH and LH was noted, but values for prolactin and
    thyroid-stimulating hormone remained unchanged. No statistical
    differences in gonadotropin-releasing hormone (GnRH) concentrations
    were present in the mediobasal hypothalamus, although an elevation
    in anterior hypothalamic GnRH values was found at the 50-mg/kg dose,
    followed by a dose-related decline. These findings would suggest
    that carbendazim-induced testicular damage is accompanied by
    compensatory changes in the hypothalmic and pituitary regulation of
    the testes (Goldman et al., 1989).

         The above studies imply that carbendazim acts directly on the
    testes to produce a number of hormonal and pathological changes.
    Consistent with this hypothesis are the results of the study of
    Nakai et al. (1992), in which the effects of carbendazim on the
    testes, efferent ductules and spermatozoa were determined after a
    single oral dose in male Sprague-Dawley rats (Charles Rivers). In
    the first experiment, groups of 86-day-old rats were treated with 0
    or 400 mg carbendazim/kg and killed 2, 4 or 8 h later on the same
    day or 1, 4, 8, 16 or 32 days after dosing. The effect of
    carbendazim was first noted at 8 h as an increase in testicular
    weight. Testis weight continued to increase until day 4 and declined
    thereafter. On days 16 and 32, testes weights were substantially
    lower than those of controls in 5 out of 16 animals, indicating the
    variable response of individual animals. A decrease in the
    percentage of sonication-resistant sperm heads per testis occurred
    at 8 h (4 out of 8 rats affected), but this decrease was not
    significant until 24 h, when a mean decrease of 19% was observed.
    Maximum decreases in total sperm head counts per testis occurred on
    day 8, after which some recovery was apparent. Epididymal weights

    were increased on day 4. The percentage of morphologi cally normal
    sperm in the cauda epididymus was less on day 4. By day 8, many
    spermatozoa heads were separated from their flagella and 10% of the
    heads were misshapen. Numerous sloughed round germ cells and
    cytoplasmic testicular debris were also evident. No effect on the
    percentage of motile sperm was seen at 2, 4 and 8 h or at 1 and 4
    days post-treatment. Sperm motility was significantly decreased on
    days 8 and 16. Because of the clumping and degeneration of the
    spermatozoa, quantitative estimates of the percentage motility could
    not be determined on days 8 and 16. Similarly damaged sperm were
    seen in 3 out of 8 rats on day 32, although the percentage of motile
    sperm that could be measured was similar to that of controls.

         In a second experiment by Nakai et al. (1992), groups of rats
    (between 97 and 105 days of age) were treated with a single oral
    dose of 0, 50, 100, 200, 400 or 800 mg/kg and killed on day 2 or 70
    post-treatment. On day 2, a dose-dependent increase in testicular
    weight was seen at dose levels 100 mg/kg or more. This was
    accompanied by significant increases in mean seminiferous tubular
    diameter at 400 and 800 mg/kg. At 50 mg/kg, missing immature germ
    cells were noted with round spermatids from stages I and II and
    elongated spermatids sloughed from stage VII epithelium. At 100
    mg/kg, the disappearance of germ cells was more severe and sloughing
    of elongated spermatids extended into stages XII and XIV. A detailed
    description of the spermatogenic cycle may be found in Russell et
    al. (1990). At doses higher than 100 mg/kg, missing germ cells
    extended into all stages except stages IX-XI, while, at doses of
    400-800 mg/kg, some seminifer ous epithelia were damaged so severely
    that it was difficult to identify the stage. In addition, major
    pathological changes were seen in the excurrent ducts of the testis.
    The rete testis was swollen with sloughed germ cells indicating that
    ductal blockage had occurred further down the tract. Such occlusions
    were observed in the efferent ductules of animals treated with 100
    mg/kg or more. On day 70, mean testis weight and mean seminiferous
    tubule diameter showed a dose-dependent decrease. Histologically,
    these decreases were associated with a dose-dependent increase in
    seminiferous tubular atrophy. No atrophic tubules were seen in the
    control rats. The atrophied tubules contained primarily Sertoli
    cells and occasional spermatogonia, and were surrounded by a
    thickened basement membrane. Pathological alterations were also seen
    in the efferent ductules of the treated animals, 50% or more of the
    ducts being occluded in rats dosed with 100 mg or more. The
    occlusions were characterized as compacted luminal contents,
    spermatic granulomas, mineralizations and obliteration of the
    original lumen by fibrotic connective tissue (Nakai et al., 1992).

         In a further study, carbendazim was administered to female
    Holtzmann rats (8 rats per group) by gavage (0, 25, 50, 100, 200,
    400 or 1000 mg/kg per day) during early pregnancy (days 1 to 8). A
    range of maternal parameters, including the number of implantation
    sites, body weight gain, uterine weight, implantation site size, and

    serum ovarian and pituitary hormones, was assessed following
    sacrifice at day 9. At dosages up to 400 mg/kg per day, carbendazim
    had no significant effect on any of the measured parameters but a
    trend towards increased resorptions was evident. The highest dosage
    produced reductions in maternal body weight gain, implantation site
    weight and serum LH, and an increase in serum estradiol (Cummings et
    al., 1990).

         Female hamsters were treated with a single gavage dose of
    carbendazim to identify effects of this compound during the
    perifertilization period. The exposure times were selected to
    coincide with either of the two microtubule-dependent events
    initiated by the ovulatory surge of LH, i.e. oocyte maturation
    (first meiotic division, occurring late on vaginal proestrous) or
    fertilization (second meiotic division, occurring early on vaginal
    estrous). In the first experiment, 0, 250, 500, 750 or 1000 mg
    carbendazim per kg (10 hamsters per group) was administered during
    meiosis I. Pregnancy outcome was assessed on day 15. The percentage
    of pregnant hamsters was significantly reduced at 750 and 1000
    mg/kg. In those animals that became pregnant, the average number of
    live pups was reduced at all dose rates. In a second experiment,
    female hamsters (10 hamsters per group) were bred overnight and
    administered a single dose of 0 or 1000 mg/kg during meiosis II on
    the morning following breeding. The percentage of pregnant hamsters
    was unaffected, but the average number of live pups (measured at 15
    days) was reduced. These results show that carbendazim
    administration by gavage at microtubule-dependent meiotic events can
    result in early pregnancy loss in hamsters (Perreault et al., 1992).

         In a separate study, pseudopregnant rats (induced by
    stimulation of the uterine cervix with a small brass rod on
    proestrous and estrous) were administered 0 or 400 mg carbendazim/kg
    per day during days 1-8. On day 4 of pseudopregnancy, a uterine
    decidual cell response was induced and the females were killed on
    day 9. The decidual cell response, evaluated as a measure of uterine
    competency, was significantly less in the treated rats than in the
    controls (Cummings et al., 1990).

         Groups of male mice (12 per group) were administered
    carbendazim (0, 250, 500 or 1000 mg/kg per day) by gavage for 5
    consecutive days. Body weights, testis weights and sperm parameters
    were measured at 7, 24 and 39 days post-treatment. Body weights were
    unaffected. Testis weights were reduced only in the highest-dose
    group at 7 and 24 days but had recovered by 39 days. Flow cytometry
    measurements of testicular cells showed that the relative
    percentages of certain testicular populations (round, elongating and
    elongated spermatids) at the highest-dose group were different from
    the control pattern 7 and 24 day after treatment (Evenson et al.,
    1987).

    7.5.2  Embryotoxicity and teratogenicity

         Carbendazim (95% purity) was administered by gavage to female
    Holtzman rats at dose levels of 0, 100, 200, 400 or 600 mg/kg body
    weight per day during days 1-8 of gestation, and the rats were then
    sacrificed on days 11 or 20. Maternal toxicity was not observed at
    any dose level. At day 11, the crown-rump length, head length,
    number of somites and number of embryos per dam were significantly
    reduced in groups receiving dosages of 200 mg/kg body weight per day
    or more. Open posterior neuropores and limb anomalies were observed
    more frequently at dosages equal to or greater than 200 mg/kg body
    weight per day. At day 20, increased resorptions, decreased live
    litter size and fetal body weight and delayed ossification was
    observed at all dosages. Skeletal malformations at the high dosage
    levels were attributed to carbendazim exposure. The authors noted
    that developmental alterations occurred at stages after the
    termination of dosing, suggesting that either the anomalies
    represent delays in development or the embryonic cells are
    vulnerable at earlier stages than was previously thought (Cummings
    et al., 1992).

         Carbendazim, in a 0.5% aqueous suspension of methyl cellulose,
    was administered by gavage to Crl:CDBR rats (25/dose group) on days
    7-16 of gestation at daily doses of 0, 5, 10, 20 or 90 mg/kg per
    day. Maternal toxicity was seen only at the highest dosage in the
    form of depressed weight gains during the dosing periods and prior
    to sacrifice on day 22. Mean values for liver weight and
    liver-to-body weight ratio were increased. Decreased pregnancy rate
    was observed at the highest dosage. An increase in the incidence of
    early resorptions per dam, decreased litter size, and the total
    resorption of three litters occurred at the highest dosage, only the
    reduction in females per litter being significant. Significant
    reductions in mean fetal weight were observed at both 20 and 90
    mg/kg per day. A significant increase in the incidence of fetal
    malformations was also seen at 90 mg/kg per day. The malformations
    consisted primarily of hydrocephaly, microphthalmia, anophthalmia,
    malformed scapulae and axial skeletal malformations (vertebral, rib
    and sternebral fusions, exencephaly, hemivertebrae and rib
    hyperplasia) (Alverez, 1987). The no-observed-effect levels (NOEL)
    for the dam and fetus were 20 and 10 mg/kg per day, respectively.

         In a further study, Delatour & Besse (1990) reported
    embryotoxic effects in eleven Sprague-Dawley rats administered 19.1
    mg carbendazim/kg per day by gavage from days 8 to 15 of gestation
    and sacrificed at day 21. The authors reported statistically
    significant (P < 0.05) increases in dead fetuses and fetal skeletal
    and external malformations, and a statistically significant decrease
    in fetal weight in the treated group. Since only one dose was used,
    it was not possible to determine a NOEL.

         The effects of carbendazim on fetal survival and development
    were studied by Janardhan et al. (1984) in rats and rabbits. Female
    Wistar-rats (8-10 per group) were given carbendazim (98% purity) by
    gavage (0, 20, 40 and 80 mg/kg per day) on days 6 to 15 of
    pregnancy. Half of each group of animals was killed on day 21 of
    gestation and half was allowed to deliver normally. Female albino
    rabbits were given 0, 40, 80 and 160 mg carbendazim/kg per day by
    gavage on days 6 to 18 of pregnancy and were sacrificed on day 31.
    All sacrificed animals were scored for live and dead fetuses and for
    resorptions; live fetuses were killed and examined for
    abnormalities. After normal deliveries, neonatal deaths and
    survivors were counted; survivors were weighed and examined for
    gross abnormalities. In rats sacrificed on day 21, dead and resorbed
    fetuses accounted for 29% of conceptuses in controls, 48% at a
    dosage of 20 mg/kg per day, and 64 to 73% at dosages of 40 and 80
    mg/kg per day. In rabbits, dead and resorbed fetuses formed 0% of
    total conceptuses in controls and 15, 21.7 and 33.3% at 40, 80 and
    160 mg/kg per day, respectively. There were no differences among the
    various groups of rats or rabbits with respect to mean weight of
    live fetuses, and there were no malformations. In rats giving birth,
    the average number of live pups per litter was close to 8 in
    controls, 6 at 20 mg/kg per day, and about 5 at 40 and 80 mg/kg per
    day. Mean fetal weight was increased by about 13% over controls at
    the two highest dosages. There were no still births, neonatal deaths
    or gross abnormalities, but mortality at 21 days postpartum was 3.0
    to 3.5 times greater at the two highest-doses compared to control
    (Janardhan et al., 1984).

         Suspensions of carbendazim (in aqueous 0.5% carboxymethyl-
    cellulose) were administered by gavage on days 7 to 19 of presumed
    gestation to artificially inseminated New Zealand white rabbits (20
    rabbits per group). Dose levels were 0, 10, 20 and 125 mg/kg per day
    (based on active ingredient) in a volume of 5 ml/kg. The
    administration of 125 mg/kg per day inhibited average maternal
    weight until day 16 of gestation. There was a slightly decreased
    implantation rate at 20 and 125 mg/kg per day and an increased
    incidence of resorption at 125 mg/kg per day. These effects resulted
    in a decreased live litter size at these two dosages. At 125 mg/kg
    per day, litters showed decreased fetal body weight, but the effect
    was not statistically significant. The average percentage of
    malformed fetuses per litter was significantly increased at 125
    mg/kg per day. Compound-related malformations at the highest dosage
    consisted of malformed cervical vertebrae and interrelated
    malformation of the ribs and proximate thoracic vertebrae (Christian
    et al., 1985). The NOEL for maternal toxicity was 20 mg/kg per day
    and the NOEL for developmental toxicity was 10 mg/kg per day.

         Groups of ChR-CD rats (27-28 pregnant rats per group) were
    administered carbendazim (53% a.i.) in their diet at levels of 0,
    100, 500, 2500, 5000, 7500 and 10 000 mg/kg from day 6 to day 15 of
    gestation. Average doses were equivalent to 0, 8.9, 45.9, 218.4,
    431.6, 625.5 and 746.9 mg/kg body weight per day, respectively. On
    day 20 of gestation, all pregnant animals were sacrificed and
    fetuses delivered by Caesarean section. There was no mortality, no
    adverse effect on body weight or clinical signs of toxicity. Food
    intake was reduced at the highest-dose level during the period the
    test diet was administered, but returned to control levels from days
    16 to 20. The number of implantation sites, resorption sites and
    live/dead fetuses were not adversely affected by carbendazim
    (Sherman, 1970). After evaluating this study, the 1983 JMPR
    concluded that there were no external or internal abnormalities
    reported that could be considered compound-related. However, no
    individual litter data were presented (FAO/WHO, 1985b).

         In a further study (Koeter, 1975a), pregnant Wistar-SPF rats
    (18-22 per group) were administered carbendazim in the diet at
    dosage levels of 0, 600, 2000 and 6000 mg/kg from days 6 to 15 of
    gestation. No individual animal or litter data were reported, and
    variations in ossification and other skeletal abnormalities were
    presented as percentages. Therefore, the teratogenic or fetotoxic
    potential of carbendazim to pregnant Wistar-SPF rats cannot be
    determined from the results and data presented (FAO/WHO, 1985b).

         Groups of pregnant New Zealand albino rabbits (3-11 per group)
    were administered carbendazim in the diet at dosage levels of 0,
    600, 2000 and 6000 mg/kg from day 6 to 18 of gestation (Koeter,
    1975b). There was a significant increase in the number of
    supernumery ribs (bilateral) and skull bones in the highest-dose
    group and ossification was significantly delayed or absent in these
    fetuses. However, there were no individual animal or litter data,
    variations in ossification were presented as percentages, and
    visceral anomalies were evaluated in only two of the four groups.
    The teratogenic potential of carbendazim to pregnant New Zealand
    albino rabbits, therefore, cannot be ascertained from the results
    and data presented (FAO/WHO, 1985b).

    7.6  Mutagenicity and related end-points

         Numerous studies have been conducted to assess the mutagenic
    potential of carbendazim. Many of the results are conflicting and
    many of the study reports do not provide sufficient detail to
    evaluate the reasons for the conflicting data. Prior to the
    mid-1980s, industrially produced carbendazim contained phenazine
    impurities. Therefore, different degrees of purity of carbendazim
    might account for some of the discrepancies. Table 9 presents those
    studies that reported sufficient experimental detail and data.

         Carbendazim is not a heritable gene mutagen. It does not
    interact with cellular DNA, induce point mutations or result in germ
    cell mutations. This has been demonstrated in both mammalian and
    non-mammalian systems  in vitro and  in vivo, and in somatic cells
    as well as in germ cells. Positive results have occasionally been
    obtained in gene mutation studies, but this was due to the presence

    of phenazines. These contaminants are mutagenic at very low
    concentrations in the  Salmonella typhimurium Ames test and also in
    the mouse lymphoma Y5178Y TK+/- gene mutation assay.
    Concentrations of > 4 mg diaminophenazine/kg and 10 mg
    aminohydroxyphenazine/kg resulted in positive  Salmonella
     typhimurium Ames test results. Process changes by some of the
    major carbendazim manufacturers have removed the phenazines. This
    contaminant is not present when other benzimidazoles such as benomyl
    or thiophanate-methyl are metabolized to carbendazim. Carbendazim
    does cause numerical chromosome aberrations (aneuploidy and/or
    polyploidy) in experimental systems  in vitro and  in vivo.


    
    Table 9.  Studies on mutagenicity of carbendazim
                                                                                                                                              
    End-points/Tests             Species, strains              Concentration           Activation     Result                  Reference
                                                                                                                                              

    1.  DNA damage and repair

                                  Bacillus subtilis              20-1000 µg per          without      negative                Shirasu et al.
                                                                 disk                                                         (1977)

                                  Salmonella typhimurium        125-2000 µg/plate         NR          negative                Rashid & Mumma
                                 (TA1535, TA1938)                                                                             (1986)

                                  Escherichia Coli,  K-12       125-2000 µg/plate         NR

                                  E. Coli,  WP2                 125-2000 µg/plate         NR          negative

    Sister chromatid exchanges   CHO cells                      0.13-40.0 µg/ml         without       negative                Ivett (1984)

                                                                1.25-40.0 µg/ml          with         negative

    Sister chromatid exchanges   human lymphocytes              0.03-30.0 µg/ml         with and      negative                Banduhn & Obe
                                                                                        without                              (1985)

    Sister chromatid exchanges   human lymphocytes               1-60 µg/ml             with and   marginal positive          Pandita (1988)
                                                               (technical grade)        without    at 30 µg/ml and above

    Unscheduled DNA synthesis    male mouse hepatocytes         0.125-12.5 µg/ml                                               Tong (1981a,b)

                                 male rat hepatocytes           0.0125-12.5 µg/ml

    Unscheduled DNA synthesis    rat hepatocytes                1.04-104.0 µg/ml                     negative                  Litton (1981)
                                                                                                                                              

    Table 9 (contd).
                                                                                                                                              
    End-points/Tests             Species, strains              Concentration           Activation     Result                  Reference
                                                                                                                                              

    2.  Gene mutation

     (1) Bacterial gene           S. typhimurium,  TA1535,       4-2500 µg/plate         with and     negative                Gericke (1977)
         mutation assays         TA1537, TA98, TA100                                     without

      Overlay spot test           S. typhimurium, his  G46,      50-100 µg/spot                       weak mutagenic          Fiscor et al.
                                 TA1530, TA1950                                                       activity at 100 µg/spot (1978)

      Plate incorporation assay  TA100                           50-200 µg/plate           NR         negative                Fiscor et al. (1978)

      Spot, liquid culture &      S. typhimurium, his            0.25-10 000 µg/ml                    negative                Fiscor et al.
      host mediated assays       G46, TA1530, TA1535,                                                                         (1978)
                                 TA1950

      Plate incorporation assay   S. typhimurium  (TA1535,       5-1000 µg/plate         with and     negative                Shirasu et al.
                                 TA1537, TA1538, TA100)                                  without                              (1977)

                                  E. coli,  WP2  hcr             5-1000 µg/plate         with and     negative                Shirasu et al.
                                                                                         without                               (1977)

                                  S. typhimurium  (TA98,         1-300 µg/plate          with and     negative                Pandita (1988)
                                 TA100)                                                  without

                                  S. typhimurium  (TA1537,       5000 µg/plate                        positive in TA1537      Albertini (1989)
                                 TA1538, TA97, TA98)                                                  & TA97 (using a
                                                                                                      pre-incubation assay),
                                                                                                      positive in TA1538 &
                                                                                                      TA98 only with
                                                                                                      activation

                                  S. typhimurium  (TA1535,       100-10 000a  µg per      with and    positve at 5000 µg/     Donovan (1982)
                                 TA1537, TA98, TA100)            plate                    without     plate with activation
                                 in TA98, TA1537
                                                                                                                                              

    Table 9 (contd).
                                                                                                                                              
    End-points/Tests             Species, strains              Concentration           Activation     Result                  Reference
                                                                                                                                              

                                  S. typhimurium  (TA1535,       up to 10 000b  µg       with and     negative up to          Russell (1983)
                                 TA1537, TA98, TA100)            per plate               without      10 000 µg/plate

                                  S. typhimurium                                                      positive if             Arce (1984a,b)
                                                                                                      carbendazim samples
                                                                                                      with 4 ppm DAP or
                                                                                                      10 ppm AHP impurities

    Host mediated assay          male ICR mice                   Total dose of mice                   negative                Shirasu et al.
                                  S. typhimurium his  G46        1000, 4000 mg/kg                                             (1977)

                                  S. typhimurium  (TA1535,       2-AB                    with and     negative                Donovan (1983);
                                 TA1537, TA98, TA100)                                    without                              Russell (1977)
                                                                 100-10 000 µg/plate
                                                                 5-HBC 200-20000 µg/plate             negative

     (2) Yeast & fungal           A. nidulans                    2.77 µM                 without      increase in frequency   Speakman & Nirenberg
         mutation assays                                         (0.53 µg/ml)                         of colonies resistant   (1981)
                                                                                                      to carbendazim

                                  Cladosporium cucumerinum       0.58 µM                 without      no effect on frequency  Speakman & Nirenberg
                                                                 (0.11 µg/ml)                         of colonies resistant   (1981)
                                                                                                      to carbendazim

                                  Saccharomyces cerevisiae       10-40 µg/ml                          negative                Albertini (1991)
                                 D7
                                                                                                                                              

    Table 9 (contd).
                                                                                                                                              
    End-points/Tests             Species, strains              Concentration           Activation     Result                Reference
                                                                                                                                              

     (3)  In vitro gene mutation
         assays

     HGPRT                       CHO cells                       3-628 µM                with         negative                Waterer (1980)
                                                                 3-654 µM                without

     forward mutation            mouse L5178Y                    50-250 µM               with and     positive with           Jotz (1980)
     at TK locus                 lymphoma cells                                          without      activation at 100 µM,
                                                                                                      negative without
                                                                                                      activation

     (4) Insect germ cell
         gene mutation

     Sex-linked recessive         Drosophila melanogaster        0.5 mg/ml                            negative                Lamb & Lilly
     lethals                                                     in DMSO                                                      (1980)
     Germline aneuploidy          D. melanogaster,  FIX,         400-50 000 ppm                       negative                Osgood et al.
                                 ZESTE                           feeding to larvae or                                         (1991)
                                                                 young adult females

     (5)  In vivo mammalian        mouse embryos treated  in                                          200 mg/kg positive      Fahrig & Seiler
         gene mutation assays      utero  by dosing the mother                                                                 (1979)
                                  100-300 mg/kg orally

    3.  Chromosomal effects

     (1)  In vitro  chromosomal     S. cerevisiae                0.001-0.100 mg/ml                    maximum responses       Whittaker et al.
         effect                                                                                       for mitotic & meiotic   (1990)
                                                                                                      chromosome gain at 0.05
                                                                                                      and 0.025 mg/ml

                                  S. cerevisiae                  5 µg/ml                              positive for            Albertini (1991)
                                                                                                      aneuploidy
                                                                                                                                              
    Table 9 (contd).
                                                                                                                                              
    End-points/Tests             Species, strains              Concentration           Activation     Result                Reference
                                                                                                                                              

                                 human lymphocytes               0.1-10.0 µM             with and   not clastogenic,          Banduhn & Obe
                                                                                         without    but induce               (1985)
                                                                                                    micronuclei at > 10 µM

                                 human lymphocytes               0.5 mg/ml               without    did not increase          Lamb & Lilly
                                                                                                    chromosome               (1980)
                                                                                                    aberration frequency

     (2)   In vivo  mammalian
          chromosomal effect

                                 male & female Sprague-          single oral dose                     did not increase        BASF (1975);
                                 Dawley rat bone marrow          300 mg/kg                            chromosome              FAO/WHO (1985b)
                                 cells                                                                aberration frequency

                                 Chinese hamster bone            oral, 1000 mg/kg                     did not produce         Seiler (1976)
                                 marrow cells                                                         chromosome breakage

                                 ICR mice nucleated              2 oral dose of                       exhibit lagging         Seiler (1976)
                                 anaphase cells                  1000 mg/kg                           chromosome, bridge
                                                                                                      formation, tripolar
                                                                                                      spindle formation, etc

                                 Mouse bone marrow               500 mg/kg                            did not detect          Seiler (1976)
                                                                                                      micronuclei

                                 Swiss albino mice               0, 200, 1000, 2000,                  dose dependent          Pandita (1988)
                                                                 4000 or 6000 mg/kg i.p.              increase in
                                                                                                      micronucleus

                                 male Chinese hamsters           0, 100, 500 or                       no effect on            Pandita (1988)
                                 bone marrow                     1000 mg/kg i.p.                      hyperploidy
                                                                                                                                              

    Table 9 (contd).
                                                                                                                                              
    End-points/Tests             Species, strains              Concentration           Activation     Result                Reference
                                                                                                                                              

     (3)   In vivo germ cell
          chromosomal mutation

     Mouse dominant lethal       NMRI mice                       500 mg/kg i.p. per                   did not exhibit a       Hoechst (1974)
     test                                                        day, 5 days                          dominant lethal effect

                                 male NMRI mice                  300 mg/kg gavage                     did not exhibit a       Hoechst (1974)
                                                                 per day, 5 days                      dominant lethal effect
                                                                                                                                              

    a Phenazin concentration in carbendazim: 9 ppm DAP, 5 ppm AHP
    b Phenazin concentration in carbendazim: < 0.6 ppm DAP, < 4 ppm AHP
      DAP = diaminophenazine; AHP = aminohydroxyphenazine; i.p. = intraperitoneal; NR = not reported
    
    7.7  Carcinogenicity

         In a study by Wood (1982), groups of CD-1 mice (80 males and 80
    females per group) were administered carbendazim (99% a.i.) in the
    diet at dose levels of 0, 500, 1500 and 7500 mg/kg diet for two
    years. The highest-dose was reduced to 3750 mg/kg after 66 weeks for
    the males because of increased mortality (62 surviving controls, 32
    surviving at 7500 mg/kg); females, however, received 7500 mg/kg
    throughout the study period. Animals were 6-7 weeks old at the start
    of this study. Mortality was compound-related in male mice. The
    high-dose males were sacrificed at week 73 because of a significant
    increase in mortality (23 surviving). Only nine males in the
    1500-mg/kg group survived to week 104, compared with 18 surviving
    control males. Females did not show this increase in mortality.

         There were no dose-related effects on body weight or food
    consumption at any time during the study, although terminal body
    weights for the low- and mid-dose males were less than those of the
    control and high-dose males. Clinical data were similar for all
    treatment and control groups. Haematological measures were
    unaffected.

         Both absolute and relative thymus weights were significantly
    decreased in females at 500 and 1500 mg/kg, but not in the high-dose
    group. Absolute liver weight was increased in the high-dose females
    and relative liver weight at the two highest-dose levels. The organ
    weights of male mice were variable and only the kidney and thymus
    weights appeared to be decreased as a result of treatment. Absolute
    kidney and thymus weights were depressed in male mice at all
    treatment levels, but relative kidney and thymus weights were
    significantly decreased only in the high-dose males. Histological
    examination revealed dose-related changes in the thymus (lymphoid
    depletion) and accumulation of yellow-brown pigment in the renal
    tubules for mid- and high-dose male mice.

         Examination of the testes demonstrated an increase in the
    frequency of sperm stasis in mid- and high-dose males, together with
    increased germinal cell atrophy (bilateral only). There was no
    trend, however, towards unilateral germinal cell atrophy, the
    incidence in controls being greater than or equal to that of treated
    males. These effects are, therefore, not considered to be
    compound-related.

         The examination of male mice livers revealed a significant
    hepatotoxic effect at 1500 and 7500 mg/kg, demonstrated by
    centrilobular hypertrophy, necrosis and swelling. There was no
    increase in the frequency of hepatocellular adenomas; these occurred
    with equal frequency in control and treatment groups. There was a
    significant increase in hepatocellular carcinomas but only at 1500
    mg/kg. However, too few males survived at the high-dose level to 17

    months (510 days) to support the conclusion of no oncogenic effect
    at that dose level.

         The occurrence of total hepatic tumours (hepatocellular
    carcinomas, hepatocellular adenomas and hepatoblastomas) is given in
    Table 10. This was statistically increased (P < 0.05) for the low-,
    mid-, and high-dose females. It was also statistically increased (P
    < 0.05) in mid-dose males but was not evaluated in high-dose males
    because of the high rate of mortality.

         In conclusion, this study on CD-1 mice showed that there were
    statistically significant increases (P < 0.05) in the incidence of
    hepatocellular carcinoma at 1500 mg/kg for males and at all dose
    levels for females, the response being dose-related (P < 0.05).
    Because of high mortality in the high-dose males, a dose-response
    relationship could not be determined. In addition, the high mor
    tality rate in male controls further hampered the interpretation of
    results. Histopathological analysis of the hepatocellular tumours in
    the test animals showed no difference from controls, and the median
    latent period for development of these hepatocellular carcinomas
    showed no significant decrease in the test animals. No carcinogenic
    effect was observed in tissues other than the liver (Wood, 1982).

         In a study on SPF Swiss mice (100 males and 100 females per
    group), carbendazim was administered in the diet at dosage levels of
    0, 150, 300 and 1000 mg/kg diet for 80 weeks. The highest-dose was
    increased to 2000 mg/kg at week 4 and to 5000 mg/kg at week 8 for
    the remainder of the study. Animals were examined for behaviour and
    clinical signs of toxicity, and body weight measurements were
    determined throughout the study. Gross pathology investigations were
    performed on all animals, liver and kidney weights were recorded,
    and tissues were examined microscopically. There were no
    compound-related effects on general condition, mortality or body
    weight. Survival at term was 70% for males and 80% for females.
    Relative liver weights for high-dose males and females were
    significantly different from those of controls, but there were no
    changes in kidney weights. The results are shown in Table 11. The
    combined incidence of hepatocellular adenomas and hepatocellular
    carcinomas increased with increasing dose levels for both males and
    females. Males showed a more pronounced induction of liver tumours
    and a more frequent occurrence of hepatocellular carcinomas which
    were often found simultaneously with hepatocellular adenomas.
    Females, on the contrary, showed only hepatocellular adenomas in
    most cases (Beems et al., 1976; Mohr, 1977).


    
    Table 10.  Incidence of combined primary hepatocellular tumours and mean and median period for development
               after treatment with carbendazim in CD-1 micea
                                                                                                                             
                                                            Male mice                                   Female mice
                                                                                                                              
    Carbendazim concentration (mg/kg diet):      0        500      1500     7500 (3750)       0        500      1500     7500
                                                                                                                             

    Combined incidences of hepatic tumours        13       20      23b      NAc                 1       9b       21b      15b

    Median period for development (days)         633      697      651      NAc               732      724      697      733

    Mean period for development (days)           628      671      628      NAc               732      706      689      653

    Number of mice examinedd                      80       80       80       80               79       78       80       78

    Median survival time (weeks)                  79       72       69       64                91       91       91       91

    Number of mice alive at termination           18       14       9        23                22       15       13       20
                                                                                                                                

    a From: Wood (1982)
    b Significant by Fisher's Exact Test at P < 0.05 level of probability
    c NA = not applicable. This group was terminated after 516 days on test (test week 73) due to a high rate of mortality. In
      view of the early termination of this test group and low incidence of hepatic tumours observed in this group, the inclusion
      of its data in statistical evaluation of hepatic tumour incidence is considered inappropriate.
    d Mice found dead or sacrificed  in extremis prior to each group's termination were subjected to gross pathological evaluation.

    Table 11.  Incidence of proliferation lesions of the hepatocytes in Swiss micea
                                                                                                                                
                                                            Male mice                                   Female mice
                                                                                                                              
    Carbendazim concentration (mg/kg diet):      0        150      300      5000              0        150      300      5000
                                                                                                                                

    Number of animals examinedb                100       94       98       100               94       99       98       95

    Liver nodular hyperplasiac                   0        8        11       25                0        5        3       11

    Hepatocellular adenoma                        9        5        13       14                1        1        3        8
                                     
    Hepatocellular carcinoma                      1        3        4        9                 1        0        0        0
                                                                                                                                

    a Adapted from: Mohr (1977)
    b A number of animals could not be examined because of well-advanced autolysis. In addition, slides were not available for
      some of the animals.
    c Values for this non-neoplastic lesion included all types of cellular alteration. A statistical analysis was not conducted.
    

         In a study on HOE NMRKf (SPF 71) mice (100-120 males and
    females per group), carbendazim was administered in the diet for 96
    weeks at dosage levels of 0, 50, 150, 300 and 1000 mg/kg diet. The
    highest-dose was increased to 2000 mg/kg at week 4 and to 5000 mg/kg
    at week 8 for the remainder of the study. Animals were examined for
    behaviour and general condition, as well as for body weight,
    food/water consumption and mortality. Gross necropsies were
    performed on all animals, liver and lung weights were recorded, and
    all organs and tissues were examined microscopically. An interim
    sacrifice was made at 18 months of 20 males and 20 females from the
    control group and the highest-dose group.

         There were no compound-related effects on behaviour, body
    weight gain, food/water consumption or mortality. At 22 months there
    was 24-31% mortality in male mice and 37-52% mortality in females in
    all groups of mice. As there was no difference between the treated
    and control groups, it was concluded mortality was not influenced by
    the feeding of carbendazim. The mean daily consumption of
    carbendazim in mg/kg body weight for males and females,
    respectively, was 5.8 and 7.1 at 50 mg/kg diet, 17.1 and 21.2 at 150
    mg/kg diet, 34.4 and 41.9 at 300 mg/kg diet, and 548.4 and 682.3 at
    5000 mg/kg diet.

         Examination of lung and liver weights at 18 and 22 months
    demonstrated an increase in absolute and relative liver weights in
    both male and female mice at 5000 mg/kg diet. Macroscopic and
    microscopic examination of 20 male and 20 female animals killed
    after 18 months of receiving 5000 mg carbendazim/kg revealed
    compound-related effects on the liver. All animals demonstrated
    centrilobular hypertrophy, single cell necrosis, mitotic cells and
    pigmented Kupffer cells. The tissues of the remaining 100 males and
    100 females exposed to 5000 mg/kg were evaluated at 22 months. There
    was marked liver cell hypertrophy (greater than in animals treated
    for 18 months only), clear cell foci, mitosis, inclusion bodies in
    enlarged cell nuclei, multiple cell necrosis, and greenish yellow
    pigment in Kupffer cells.

         Neoplastic nodules (adenomas), carcinomas, fibrosarcomas and
    other tumorigenic responses in the liver were equally distributed
    among all groups (Tables 12 and 13). Although haemangiomas of the
    liver (Table 14) were found in all treated groups (but not in
    controls), no dose-related response was evident. Lung adenomatosis
    was equally distributed among all groups. There was no effect of
    carbendazim on the incidence or time of onset of tumours, and the
    total number of benign and malignant tumours was comparable among
    the various groups of mice. Thus, there was no evidence of a
    carcinogenic effect from carbendazim when administered in the diet
    to mice at doses up to and including 5000 mg/kg diet for 22 months
    (Donaubauer et al., 1982).

        Table 12.  Incidence of tumours in HOE NMRKf mice after 18 months of
               exposurea

                                                                         
                                                         Mice treated with
                                        Control          5000 mg/kg diet

                                    male      female     male      female
                                                                         

    Lung
      adenoma                         3         5          4         -

    Uterus
      stromal sarcoma                           1                    -

    Ovary
      tubular adenoma                           1                    -
      granulosa cell tumour                     1                    -
      luteoma and tubular adenoma               1                    -

    Skin and subcutaneous tissue
      round cell sarcoma              -         -          -         1
      adenocarcinoma                  -         -          1         -

    Lymph nodes
      lymphosarcoma                   -         -          -         1
                                                                       
                                      3         9          5         2
                                                                       

    a Adapted from Donaubauer et al. (1982)
    
    7.8  Neurotoxicity

         Carbendazim (500, 2500 and 5000 mg/kg) has been evaluated for
    neurotoxic potential in white Leghorn hens (10 per group). Controls
    consisted of the vehicle (corn oil) and the neurotoxin tri- o-tolyl
    phosphate (TOTP). The hens were observed daily for mortality and
    clinical neurotoxicity for four weeks. Neurotoxic signs, consisting
    of leg weakness, ataxia and/or "goose-stepping" gait, were observed
    in hens treated with TOTP. Less severe and reversible signs,
    consisting of slight leg weakness and ataxia, were observed in hens
    treated with 5000 mg carbendazim/kg, but no neurotoxic signs were
    observed for those treated with 500 or 2500 mg/kg. Microscopic
    examination indicated that there was no axonal degeneration or
    demyelination in carbendazim-treated animals (Goldenthal, 1978).


    
    Table 13.  Possible preneoplastic changes and primary neoplasms in the livers and lungs of HOE NMRKf mice
               after 22 months of exposurea
                                                                                                                  
    Carbendazim concentration:         0               50               150              300              5000
    (mg/kg diet)                  male  female     male  female     male  female     male  female     male  female
                                                                                                                  

    Liver

     Neoplastic nodules
     (adenomas)                     3                2                                         1        1
     Clear cell foci                                                                                    3       4
     Basophilic foci                                         1        1
     Haemangiomas (liver)                            2                3                2       2                1

    Lungs

     Adenomatosis                  29      10       31       8       30      10       25       9       22      12
     Adenocarcinomas                                         1                                          1
     Keratinizing squamous
     cell carcinomas                                                          1
     Cavernous haemangioma                                   1
                                                                                                                  

                                   32      10       35      11       34      11       27      12       27      17
                                                                                                                  

    a Adapted from Donaubauer et al. (1982)
    
    Table 14.  Haemangiomas of the liver in HOE NMRKf mice after
               22 months of exposurea
                                                                       
    Dose (mg/kg diet)                  Male                     Female
                                                                       
           0                           0                        0
          50                           2                        0
         150                           3                        0
         300                           2                        2
        5000                           0                        1
                                                                       

    a Adapted from Donaubauer et al. (1982)

    7.9  Toxicity of contaminants

         When manufactured under certain conditions, carbendazim
    contains a class of contaminants called phenazines. These
    contaminants are mutagenic at very low concentrations in the
     Salmonella typhimurium Ames test and also in the mouse lymphoma
    Y5178Y TK+/- gene mutation assay. Concentrations of > 4 ppm
    diaminophenazine or 10 ppm aminohydroxyphenazine yielded positive
    results. Process changes by some of carbendazim manufacturers have
    now removed the phenazines.

    7.10  Mechanisms of toxicity - mode of action

         Biochemical studies on the mechanism of action of benzimidazole
    compounds have shown that their biological effects are caused by
    interactions with cell microtubules (Davidse & Flach, 1977). These
    cellular structures are present in all eukaryotic cells and are
    involved in several vital functions, such as intracellular
    transports and cell division. Benzimidazole compounds have been used
    as anticancer drugs and as anthelminthic drugs in animals and humans
    because they act as spindle poisons by interfering with the
    formation and/or functioning of microtubules. However, eukaryotes
    are known to be unequally sensitive to each benzimidazol compound,
    which explains the use of these compounds in helminthiases.
    Selective toxicity of benomyl and carbendazim for fungi has been
    explained by comparing their binding to fungal and mammalian
    tubulin. The different sensitivity of several fungi has also been
    explained by the different affinity of benomyl and carbendazim for
    fungal tubulin.

         Benomyl has been found to bind to fungal tubulin but not to
    porcine brain tubulin, indicating that mammalian tubulin has no, or
    at least low, affinity for benomyl (Davidse & Flach, 1977). This is
    in agreement with the observation that benomyl at concentrations
    that are lethal for sensitive fungi does not interact with  in vitro
    microtubule assembly in these brain extracts.  In vitro ID50
    values for several mycelial extracts of various fungal species

    sensitive to benomyl were all below 5 µmol/litre (Davidse & Flach,
    1977).  In vitro rat brain tubulin polymerization was inhibited to
    about 20% at benomyl or carbendazim concentrations of 25 µmol/litre
    (De Brabander et al., 1976b). For comparison, a standard antitubulin
    drug in humans such as vincristine inhibited 50% tubulin assembly at
    0.1 µmol/litre in the same experiment. The assembly of sheep and
    calf brain microtubule was also found to be unaffected by
    carbendazim concentrations higher than 100 µmol/litre (Ireland et
    al., 1979).

         Mitotic arrest by benzimidazole and six analogues at metaphase
    was evaluated in human lymphocyte cultures. Structure-activity
    relationships indicate that antimitotic activity is related to C6
    substitution of the benzimidazole moiety (Holden et al., 1980). In
    this study, however, benomyl and carbendazim were not tested. The
    question of whether all C6 unsubstituted benzimidazoles, such as
    benomyl and carbendazim, have no effect on mitosis of human
    lymphocytes in cell cultures is therefore unresolved.

         A link between the effects of benomyl and carbendazim on
    tubulin and their teratogenic effects has been postulated (Ellis et
    al., 1987, 1988).

    8.  EFFECTS ON HUMANS

    8.1  General population exposure

         No references to carbendazim poisoning have been documented in
    the literature. Recent data to estimate dietary exposure of the
    benzimidazole benomyl, based on food consumption patterns within the
    USA and elsewhere, indicate exposure below the NOELs from animal
    toxicity tests. Further information is given in section 5.2.1 of
    Environmental Health Criteria 148: Benomyl (WHO, 1993).

    8.2  Occupational exposure

         Selected blood profiles from 50 factory workers involved in the
    manufacture of benomyl and carbendazim were compared to those of a
    control group of 48 workers who were not exposed to these two
    fungicides. White blood cell count, red blood cell count, and
    haemoglobin and haematocrit values were comparable among the two
    groups. There were no quantitative estimates of exposure given for
    the factory workers. No female employees were included in the
    control group (Everhart, 1979; FAO/WHO, 1985a).

         A study was performed to determine whether exposure to benomyl
    and carbendazim had an adverse effect on the fertility of 298 male
    manufacturing workers exposed to benomyl between 1970 and 1977. The
    workers ranged from 19 to 64 years of age (79% were between 20 and
    39, and 78% of the spouses were similarly aged between 20 and 39
    years). Exposure duration ranged from less than one month to 95
    months, and more than 51% of the workers were potentially exposed
    from 1 to 5 months. The birth rates of exposed workers' spouses were
    compared with those of four comparison populations from the same
    county, state, region and country (USA). There was no reduction in
    fertility as shown by the birth rates for the study population,
    which were generally higher than the comparison populations.
    Spermatogenesis among workers was not examined (Gooch, 1978;
    FAO/WHO, 1985a).

    9.  EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD

    9.1  Microorganisms

         Studies on soil effects have concentrated on benomyl. However,
    carbendazim, the breakdown product of benomyl, would be expected to
    produce comparable results.

         Soil respiration has been found to be little influenced by
    benomyl at concentrations below 10 mg/kg, which is the maximum soil
    concentration expected after use at recommended application rates
    (Hofer et al., 1971; van Fassen, 1974; Peeples, 1974; Weeks &
    Hedrick, 1975).

         A study on the influence of benomyl on soil nitrogen
    mineralization showed that the release of ammonia was not decreased
    by benomyl, whereas the influence of the fungicide on nitrification
    varied from a stimulation (van Fassen, 1974), through no effect
    (Mazur & Hughes, 1975), to a decreased nitrification (Hofer et al.,
    1971; Wainwright & Pugh, 1974). The differences may be related to
    the soil composition since Hofer et al. (1971) found a greater
    effect in sandy than in organic soil.

         Benomyl, in combination with eleven other pesticides that were
    used in an orchard spray programme, had only a minimal and
    short-term effect on respiration, ammonification and nitrification
    at concentrations expected after recommended use of benomyl over a
    spraying season. Ten times the recommended application rates had a
    pronounced effect on both respiration and nitrification, which
    lasted for more than 4 weeks (Helweg, 1985).

         The influence of benomyl and carbendazim on soil microbial
    activity was studied in Sweden following repeated annual
    applications during autumn to winter cereals for a period of 3 to 5
    years. The effects of the fungicides on straw decomposition, balance
    of straw fungal flora and nitrogen mineralization in the soil were
    investigated in field and laboratory experiments. The decomposition
    of straw in the field was not affected in clay soils by annual
    applications of up to 2 kg/ha. In sandy soils, rates of up to 0.5
    kg/ha had no effect, but in one case at 2 kg/ha the initial stages
    of straw decomposition were slightly inhibited. All doses tested in
    both clay and sandy soils caused changes in the composition of the
    straw fungal flora (Torstensson & Wessen, 1984).

         Tests were conducted to determine the effects of the fungicide
    carbendazim (Bavistin), the herbicide fluometuron (Cotoran) and the
    insecticide curacron on Egyptian soil fungi when applied at the
    recommended field rates and at 4 and 8 times these rates.
    Carbendazim produced a significant inhibition of the total count of
    fungi at all three rates after 5 and 40 days and at the higher
    application rates after 80 days. The response of  Aspergillus sp.

    alone to this fungicide reflected the effects on the total fungal
    count (Abdel-Fattah et al., 1982).

         An application of carbendazim (5 mg formulation/kg soil) and
    Calixin (1.5 mg formulation/kg soil) significantly enhanced the
    microbial activity, as well as the availability of ammonium nitrogen
    and phosphate in the soil, while nitrite, nitrate and available
    potassium were found to decrease. During incubation, CO2 evolution
    decreased during the first 21 days, increased up to 42 days, and,
    thereafter, decreased with both treatments (Khan et al., 1987).

    9.2  Aquatic organisms

         The effect of carbendazim was monitored using the green alga
     Selenastrum capricornutum in an OECD guideline test (201). The
    EC50 (based on total growth) at 72 h was 1.3 mg/litre and at 120 h
    was 1.6 mg/litre. The no-observed-effect concentration (NOEC) was
    0.5 mg/litre. To study whether carbendazim was algistatic or
    algicidal, organisms were recultured at the end of the initial 120 h
    of incubation. Regrowth occurred in the control but not in the test
    cultures (8.0 mg/litre) after a period of 9 days. Carbendazim was,
    therefore, considered to be algicidal (Douglas & Handley, 1987). In
    another study using  Chlorella pyrenoidosa, the 48-h EC50 for
    growth inhibition was calculated to be 0.54 mg/litre (Canton, 1976).

         The acute toxicity of carbendazim to a variety of aquatic
    organisms is summarized in Table 15. For 96-h tests, LC50 values
    ranged from 0.007 mg/litre for channel catfish ( Ictalurus punctatus
    yolk-sac fry) to 5.5 mg/litre for bluegill sunfish (Palawski &
    Knowles, 1986).

         In a static renewal 21-day test using  Daphnia magna, onset of
    reproduction was the most sensitive indicator, being significantly
    delayed at 0.025 mg carbendazim/litre (measured concentration).
    Other parameters (number of days reproducing, total number of young,
    and young produced per day) were affected significantly at 0.05
    mg/litre. The NOEC was 0.013 mg/litre (measured concentration)
    (Hutton et al., 1986).

         Gillet & Roubaud (1983) showed that the toxicity of carbendazim
    to carp ( Cyprinus carpio) was greater for the fertilization and
    early development stages than for the adult stages. They found the
    30-min LC100 during the fertilization stage to be < 5 mg/litre at
    pH 9 and < 2.5 mg/litre at pH 7. The rainbow trout ( Oncorhynchus
     mykiss) was more sensitive, with an LC100 (30 min, pH 9) of 0.5
    mg/litre and 71% survival, compared to controls, at 0.05 mg/litre.


    
    Table 15.  Toxicity of carbendazim to aquatic organisms
                                                                                                                                              
    Organism                 Size/a           Stat/  Temperature    Hardnessb    pH    Duration   LC50        Reference
                             age              flow   (°C)           (mg/litre)         (h)        (mg/litre)
                                                                                                                                              

    Freshwater

    Water flea               < 24 h           stat   20             179          7.5   48         0.087       Hutton (1988)
     (Daphnia magna)         < 24 h           stat   20                                48         0.46        Canton (1976)

    Rainbow trout            3 months         stat   15                                48         1.8         Canton (1976)
     (Oncorhynchus mykiss)   0.8 g            stat   13                          7.5   96         0.36        Heinemann (1971)
                             yolk-sac fry     stat   10             40-48        7.4   96         0.145       Palawski & Knowles (1986)
                             swimup fry       stat   10             40-48        7.4   96         0.32        Palawski & Knowles (1986)
                             0.2 g            stat   10             40-48        7.4   96         0.37        Palawski & Knowles (1986)
                             1.2 g            stat   10             40-48        7.4   96         0.87        Palawski & Knowles (1986)
                                              stat   12             40-48        7.4   96         > 1.8       Palawski & Knowles (1986)
                                              stat   17             40-48        7.4   96         0.87        Palawski & Knowles (1986)
                                              stat   22             40-48        7.4   96         0.1         Palawski & Knowles (1986)
                                              stat   10             40-48        6.5   96         0.64        Palawski & Knowles (1986)
                                              stat   10             40-48        7.5   96         0.41        Palawski & Knowles (1986)
                                              stat   10             40-48        8.5   96         0.34        Palawski & Knowles (1986)
                                              stat   10             40           7.4   96         0.78        Palawski & Knowles (1986)
                                              stat   10             320          7.4   96         0.88        Palawski & Knowles (1986)

    Bluegill sunfish         0.95 g           stat   22-23          67           7.0   96         5.5         Wetzel & Hutton (1984)
    (Lepomis macrochirus)    0.2 g            stat   22             40-48        7.4   96         > 3.2       Palawski & Knowles (1986)

    Channel catfish          yolk-sac fry     stat   22             40-48        7.4   96         0.007       Palawski & Knowles (1986)
     (Ictalurus punctatus)   swimup fry       stat   22             40-48        7.4   96         0.012       Palawski & Knowles (1986)
                             0.2 g            stat   22             40-48        7.4   96         0.01        Palawski & Knowles (1986)
                             1.2 g            stat   22             40-48        7.4   96         0.019       Palawski & Knowles (1986)
                                              stat   12             40-48        7.4   96         > 0.56      Palawski & Knowles (1986)
                                              stat   17             40-48        7.4   96         0.14        Palawski & Knowles (1986)
                                              stat   22             40-48        7.4   96         0.032       Palawski & Knowles (1986)
                                              stat   22             40-48        6.5   96         0.023       Palawski & Knowles (1986)
                                                                                                                                              

    Table 15 (contd).
                                                                                                                                              
    Organism                 Size/a           Stat/  Temperature    Hardnessb    pH    Duration   LC50        Reference
                             age              flow   (°C)           (mg/litre)         (h)        (mg/litre)
                                                                                                                                              

                                              stat   22             40-48        7.5   96         0.014       Palawski & Knowles (1986)
                                              stat   22             40-48        8.5   96         0.023       Palawski & Knowles (1986)
                                              stat   22             40           7.4   96         0.018       Palawski & Knowles (1986)
                                              stat   22             320          7.4   96         0.024       Palawski & Knowles (1986)

    Toad                     tadpole          stat   25                                48         3.5         Nishiuchi & Yoshida (1974)
     (Bufo bufo japonicus)

    Marine and Estuarine

    Eastern oyster           25-50 mm         flow   18-20                             96         > 1.145c     Boeri (1988a)
     (Crassostrea virginica)

    Mysid shrimp                              stat   23                                96         0.098       Boeri (1988c)
     (Mysidopsis bahia)

    Sheepshead minnow        0.14 g           stat   22                                96         > 1.158     Boeri (1988b)
     (Cyprinodon variegatus)
                                                                                                                                              

    a stat = static conditons (water unchanged for duration of test); flow = flow-through conditions (carbendazim concentration
      in water continuously maintained)
    b hardness given as mg CaCO3/litre
    c EC50 based on rate of shell deposition
    
         Bluegill sunfish were exposed to benomyl, carbendazim and 2-AB
    at concentrations of 0.05 mg/litre (measured concentrations 0.01 to
    0.04 mg/litre) and 5.0 mg/litre (measured concentration 2 to 5
    mg/litre). No residue was found in the tissues of fish exposed to
    low levels of these compounds, but detectable residues were found in
    the tissues of fish exposed to the high levels. However, there was
    no build-up or bioconcentration with time (DuPont, 1972).

    9.3  Terrestrial organisms

         Van Gestel et al. (1992) exposed red earthworms ( Eisenia
     andrei) to carbendazim, added as an aqueous solution of the
    formulation Derosal, to artificial soil. The final concentrations in
    soil were 0, 1, 3.2, 10, 32 and 100 mg formulation/kg dry soil,
    corresponding to 0, 0.6, 1.92, 6.0, 19.2 and 60 mg carbendazim/kg.
    The worms had been acclimatised for 1 week in the artificial soil,
    which contained 8 g cow dung per kg soil as food for the worms. The
    soil pH (7.3) was higher than optimum for this species and resulted
    in a lower cocoon production in this test than expected. At the two
    highest concentrations of 19.2 and 60 mg a.i./kg, all worms died
    over the 3 week experimental period; an LC50 of 5.7 (4.7-6.9) mg
    a.i./kg was calculated. Growth was significantly reduced at 6.0
    mg/kg soil, and reproduction (measured as cocoon production, number
    of fertile cocoons and numbers of juveniles) was significantly
    reduced at > 1.92 mg a.i./kg soil. The EC50 for cocoon
    production was calculated to be 2.9 (2.2-3.8) mg a.i./kg dry soil.
    The response curve for reproduction and growth effects of
    carbendazim was steep. Vonk et al. (1986) had reported comparable
    results for a second  Eisenia species,  E. foetida, in a different
    artifical soil; the LC50 was 9.3 mg/kg soil and the NOEC for
    cocoon production 2.0 mg/kg soil.

         Carbendazim (99.3% purity) was evaluated for acute contact
    toxicity after thoracic application in honey-bees ( Apis mellifera).
    Each treatment level consisted of four replicates of ten bees each.
    Forty bees served as positive control (using carbaryl) and forty as
    negative control. No deaths occurred after the application of 50 µg
    carbendazim/bee, the highest rate tested. Carbendazim is, therefore,
    classified as "relatively non-toxic" to the honey-bee (Meade, 1984).

         The LD50 for bobwhite quail, with an observation period of 14
    days following the single oral dose, was > 2250 mg/kg body weight
    (Beavers, 1985). For mallard ducks the dietary 5-day LC50 was >
    10 000 mg carbendazim/kg diet (Fink, 1975).

    9.4  Population and ecosystem effects

         Van Gestel (1992) has summarized reports of toxicity of
    carbendazim on earthworms from field studies based on different soil
    types, application rates and crops (Table 16). Estimated soil
    concentrations in this table are based on application rates; it has

    been assumed that there is no mobility of the compound beyond the
    top 2.5 cm of soil and homogeneous distribution of carbendazim in
    this layer. For orchard application, it was further assumed that 50%
    of the applied active ingredient reached the soil. Reported effects
    include reduced numbers, reduced activity (as reduced removal of
    leaf litter) and reduced reproduction of worms. Application rates
    were within the recommended rates for carbendazim as a fungicide on
    these crops.


    
    Table 16.  Summary of earthworm toxicity data on carbendazim in field studies
                                                                                                                 
    Crop/soil type      Dosage   Estimated soil   Time     Effect                             Reference
                        (kg/ha)  concentration    (days)
                                 (mg/kg)
                                                                                                                 
    Grass               0.3      0.9              12       11% reduction in number            Ammon (1985)

    Grass               0.56     1.6              49       72% reduction in cast production   Keogh & Whitehead
                                                           42% more litter left               (1975)

    Winter wheat/clay   0.15     0.4            275        14% reduction in juveniles         Lofs-Holmin (1981)
                                                           50% increase in adult
                                                              Allolobophora caliginosa
                                                           25% increase in juveniles
                                                           25% reduction in adult
                                                              A. chlorotica                   Lofs-Holmin (1981)

    Apples/loam         0.375a   1.6              245      reduction in litter removal        Cook & Swait (1975)
                                                                                                                 

    a Three separate applications of carbendazim
    
    10.  EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT

         Benomyl and carbendazim are two different fungicides in their
    own right. However, carbendazim is also the main metabolite of
    benomyl in mammals and the degradation product of benomyl in the
    environment. Butyl isocyanate is the chemical moiety removed from
    benomyl when carbendazim is formed. Given the similar toxicities
    caused by benomyl and carbendazim and the different toxicological
    profile of butyl isocyanate, the two fungicides are evaluated
    together in this monograph.

    10.1  Evaluation of human health risks

         The two primary routes of exposure to humans are through diet
    and through manufacturing or use of the product.

         There is limited information on actual dietary exposure to
    benomyl and carbendazim. Dietary exposure has been estimated in the
    Netherlands and the USA. In the USA, exposure based on dietary
    habits, measured residue levels, and the percentage of crop treated
    has been calculated for various subgroups of population. These
    calculations indicate that the estimated benomyl exposure is
    0.144-1.479 µg/kg per day (section 5.2.1 of Environmental Health
    Criteria 148: Benomyl (WHO, 1993)). In the Netherlands, the mean
    dietary intake was estimated to be 0.83 µg/kg per day (0.05 mg/day
    per person). These levels of exposure are below the recommended ADI
    of 0.01 (carbendazim) and 0.02 (benomyl) mg/kg body weight.

         The average air levels of benomyl and carbendazim have been
    determined in a manufacturing facility (section 5.3) and found to be
    less than 0.2 and 0.3 mg/m3, respectively. Both values are below
    the Threshold Limit Value of 5-10 mg benomyl/m3 established by a
    number of governmental agencies.

         In one study, potential respiratory and dermal exposure to
    benomyl wettable powder formulation was determined under several
    agricultural use situations (section 5.3). The highest rates of
    exposure occurred in situations of mixing and loading in preparation
    for aerial application; dermal and respiratory exposures were,
    respectively, 26 and 0.08 mg/person per cycle. Home users and
    agricultural workers re-entering treated fields were estimated to be
    exposed to about 1 mg/person per cycle and 5.9 mg/person per hour,
    principally through the dermal route.

         Because of the low mammalian toxicity, acute benomyl or
    carbendazim poisonings are unlikely to occur under conditions of
    normal use.

         Several studies of agricultural workers (section 8.2 of
    Environmental Health Criteria 148: Benomyl (WHO, 1993)) have shown
    some cases of contact dermatitis after exposure to benomyl. These

    effects can be significantly reduced or eliminated by wearing
    long-sleeved shirts, long trousers and gloves.

         There is little information on health effects in humans as a
    consequence of exposure to either benomyl or carbendazim. Two
    studies have been conducted on factory workers involved in the
    manufacture of benomyl (section 8.2). In one study, haematological
    profiles from 50 factory workers involved in the manufacture of
    benomyl were comparable to those from a control group of 48 workers.
    A second study found no decrease in the birth rate of the wives of
    298 factory workers exposed to benomyl.

         Extensive studies of various species of laboratory animals show
    reproductive, developmental, mutagenic and carcinogenic effects
    associated with both benomyl and carbendazim. The effects observed
    on rat fetuses were microphthalmia, hydrocephaly and encephaloceles.
    The no-observed-effect levels (NOEL) of benomyl for developmental
    toxicity are equal to or greater than 10 mg/kg body weight per day,
    depending upon the species and route of administration. Similarly,
    the NOEL of benomyl for reproductive effects in the male rat appears
    to be 15 mg/kg body weight per day after gavage dosing. In feeding
    studies with both benomyl and carbendazim, the NOEL appears to be
    500 mg/kg diet (equivalent to 25 mg/kg body weight per day).
    However, one benomyl feeding study reported a NOEL of less than 1
    mg/kg diet (0.05 mg/kg body weight per day) for male reproductive
    effects. The reason for the discrepancy between the NOEL in this
    latter study and other investigations is unknown.

         The only consistent genotoxic effect noted in animal studies is
    the induction of numerical chromosomal aberrations. These effects
    are consistent with the interaction of benomyl and carbendazim with
    microtubule formation.

         Rat carcinogenicity studies did not show any carcinogenic
    effect for either compound. Benomyl and carbendazim induce
    hepatocellular tumours in CD-1 and SPF Swiss mice but not in NMRKf
    mice. This finding in mice is not considered to be a result of a
    direct genotoxic action. Rather, it appears to be associated with
    liver toxicity in strains of mice that are highly susceptible to
    tumour formation at this site.

         Benomyl and carbendazim are spindle poisons. Effects on target
    cells are consequences of binding to microtubules, giving toxicities
    similar to those of other spindle poisons such as colchicine and
    vincristine. Benzimidazole compounds in general and benomyl and
    carbendazim in particular have selective effects on the microtubules
    of different eukaryotes. Reasons for this selectivity include the
    binding capability to different tubulins and pharmacokinetic
    differences across species.  In vitro concentrations of benomyl
    used to kill sensitive fungi were found to be ineffective in
    disturbing mammalian microtubular functions. These studies on the

    mechanism of action of benomyl and carbendazim indicate a selective
    effect of these compounds for target species.

         In summary, the LD50, as determined in a number of test
    species, for benomyl ranges from > 2000 to > 12 000 mg/kg and for
    carbendazim from > 2000 to > 15 000 mg/kg. There are no known
    reports of human poisoning for either compound. This, coupled with
    the low estimated environmental levels of both compounds, would
    suggest that the possibility of acute poisoning by benomyl or
    carbendazim is very remote. Similarly, the data available on test
    species make it unlikely that either benomyl or carbendazim is
    carcinogenic for humans. The NOELs for both reproductive and
    teratogenic effects of benomyl and carbendazim (i.e. 10-15 mg/kg) do
    raise a possibility that an accidental ingestion of either fungicide
    could adversely alter reproductive outcome in humans, but the
    likelihood that such poisoning would occur is remote. The
    selectivity of these two benzimidazole compounds for the tubulin of
    the target species (fungi) and their relative ineffectiveness to
    disturb mammalian microtubule function further reduce the
    possibility of their having toxic effects in humans.

    10.2  Evaluation of effects on the environment

         Benomyl is rapidly converted to carbendazim in various
    environmental compartments, the half-lives being 2 and 19 h in water
    and soil, respectively. Therefore, data from studies on both benomyl
    and carbendazim are relevant for the evaluation of environmental
    effects.

         Carbendazim persists on leaf surfaces and in leaf litter. In
    soil the half-life is between 3 and 12 months, and the compound may
    be detected for up to 3 years. However, in many cases, major
    residues will be lost within a single season. Residues of carben
    dazim and its metabolites are strongly bound or incorporated into
    soil organic matter. The strong adsorption (Koc = approximately
    2000) of carbendazim to soil and sediment particles reduces its
    bioavailability to terrestrial and aquatic organisms. Similarly, the
    mobility of carbendazim in soil is limited, and it is not expected
    to leach to ground water.

         Benomyl and carbendazim are highly toxic to some aquatic
    organisms in laboratory tests, the most sensitive species being the
    channel catfish with a 96-h LC50 for yolk-sac fry of 0.006 mg
    benomyl/litre. However, this toxicity is unlikely to be manifest in
    the environment for most aquatic organisms because of the low
    bioavailability in surface waters. The exposure of sediment-living
    organisms could be greater, but no test results are available for
    these organisms.

         Benomyl and carbendazim affect groups of fungi in soil but do
    not seem to modify the overall microbial activity of the soil when
    used at normal field rates.

         In both the laboratory and field, benomyl and carbendazim
    applied at recommended rates cause deaths and sublethal reproductive
    effects on earthworms of many different species. Surface-feeding
    species eating leaf litter are most at risk. Populations may take
    more than 2 years to recover. There are no studies available on
    other litter and soil invertebrates.

         Benomyl and carbendazim have low toxicity for birds and
    carbendazim is classified as "relatively non-toxic" to honey-bees.

    10.3  Conclusions

         Benomyl causes dermal sensitization in humans. Both benomyl and
    carbendazim represent a very low risk for acute poisoning in humans.
    Given the current exposures and the low rate of dermal absorption of
    benomyl and carbendazim, it is unlikely that they would cause
    systemic toxicity effects either in the general population or in
    occupationally exposed subjects. These conclusions are drawn from
    animal data and from the limited human data available, but these
    extrapolations are supported by the understanding of the mode of
    action of carbendazim and benomyl in both target and non-target
    species.

         Further elucidation of the mechanism of toxicity of carbendazim
    and benomyl in mammals will perhaps permit a better determination of
    no-observed-effect levels. Binding studies on tubulins of target
    cells (testis and embryonic tissues) will facilitate comparisons
    across species.

         Carbendazim is strongly adsorbed to soil organic matter and
    remains in the soil for up to 3 years. It persists on leaf surfaces
    and, therefore, in leaf litter. Earthworms have been shown to be
    adversely affected (population and reproductive effects) at
    recommended application rates. There is no information on other soil
    or litter arthropods that would be similarly exposed.

         The high toxicity to aquatic organisms in laboratory tests is
    unlikely to be seen in the field because of the low bioavailability
    of sediment-bound residues of carbendazim. However, no information
    is available on sediment-living species which would receive the
    highest exposure.

    11.  FURTHER RESEARCH

    1.   Comparative binding studies of carbendazim to tubulins of
         target tissues from various species should be undertaken.

    2.   Further clarification of the fate of 1,2-diaminobenzene and
         bound residues in the environment is needed.

    3.   The effects of benomyl and carbendazim on sediment-dwelling
         organisms needs to be investigated.

    12.  PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES

         Carbendazim was evaluated by the Joint FAO/WHO Meeting on
    Pesticide Residues (JMPR) in 1973, 1976, 1977, 1978, 1983 and 1988.
    The 1978 meeting agreed that the MRLs for benomyl, carbendazim and
    thiophanate-methyl should be combined and expressed as carbendazim.
    Carbendazim residues were last evaluated by the 1988 meeting
    (FAO/WHO, 1988b) and the MRLs were updated at that time. These MRLs
    (expressed as carbendazim) are listed in Table 4. The 1983 meeting
    (FAO/WHO, 1985a) evaluated carbendazim toxicology and set the
    following NOEL levels and ADI:

         Rat: 500 mg/kg diet, equivalent to 25 mg/kg body weight

         Dog: 100 mg/kg diet, equivalent to 2.5 mg/kg body weight

         Rat: teratology - 30 mg/kg body weight per day (benomyl)

         The estimated ADI for carbendazim was established to be 0-0.01
    mg/kg body weight.

         Carbendazim has not been evaluated by the International Agency
    for Research on Cancer (IARC).

    REFERENCES

    Abdel-Fattah HM, Abdel-Kader M, & Hamida S (1982) Effect of
    Bavistin, Cotoran and Curacron on Egyptian soil fungi.
    Mycopathologia, 80(2): 101-106.

    Albertini S (1989) Influence of different factors on the induction
    of chromosome malsegregation in  Saccharomyces cerevisiae D61.M by
    Bavistan and assessment of its genotoxic property in the Ames test
    and in  Saccharomyces cerevisiae D7. Mutat Res, 216: 327-340.

    Albertini S (1991) Reevaluation of the 9 compounds reported
    conclusive positive in yeast  Saccharomyces cerevisiae aneuploidy
    test systems by the Gene-Tox Program using strain D61.M of
     Saccharomyces cerevisiae. Mutat Res, 260: 165-180.

    Alverez L (1987) Teratogenicity study of INE-965 (carbendazim) in
    rats. Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc.,
    Haskell Laboratory (Unpublished report No. HLR 281-87).

    Amacher DE, Paillet S, & Ray VA (1979) Point mutations at the
    thymidine kinase locus in L5178Y mouse lymphoma cells: Application
    to genetic toxicological testing. Mutat Res, 64: 391-406.

    Ames BN, McCann J, & Yamasaki E (1975) Methods of detecting
    carcinogens and mutagens with the Salmonella/mammalian microsome
    mutagenicity test. Mutat Res, 31: 347-364.

    Ammon HU (1985) Worm toxicity tests using  Tubifex tubifex. In:
    Comportement et effets secondaires des pesticides dans le sol. Les
    Colloques de l'INRA 31, Versailles, 4-8 juin 1984. Paris, Institut
    national de la Recherche agronomique, pp 303-317.

    Arce GT (1984a) Mutagenicity evaluation in  Salmonella typhimurium.
    Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 72-84).

    Arce GT (1984b) Mutagenicity evaluation in  Salmonella typhimurium.
    Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 71-84).

    Arthur MF, Marsh BH, Fadel LC, & Zwick TC (1989a) Anaerobic aquatic
    metabolism of [phenyl(U)-14C] benomyl in West Jefferson, Ohio,
    pond water and sediment (Battelle Project No. N-0799-8800).
    Columbus, Ohio, Battelle, Environmental Sciences Department
    (Unpublished report No. AMR 770-87, prepared for E.I. Du Pont de
    Nemours and Co., Inc.).

    Arthur MF, Schweitzer KL, Fadel LC, Marsh BH, & Marsh SS (1989b)
    Aerobic aquatic metabolism of [phenyl(U)-14C] benomyl in
    Greenville, Mississippi, water and sediment (Battelle Project No.

    N-0966-7301). Columbus, Ohio, Battelle, Environmental Sciences
    Department (Unpublished report No. AMR 1452-89, prepared for E.I. Du
    Pont de Nemours and Co., Inc.).

    Bamburg JR, Shooter EM, & Wilson L (1973) Developmental changes in
    microtubule protein of the chick brain. Biochemistry, 12: 1476-1482.

    Banduhn N & Obe G (1985) Mutagenicity of methyl
    2-benzimidazolecarbamate, diethylstilbestrol and estradiol:
    Structural chromosomal aberrations, sister-chromatid exchanges,
    C-mitoses, polyploidies and micronuclei. Mutat Res, 156: 199-218.

    BASF (1975) Dominant lethal study: mice. Ludwigshafen, Germany, BASF
    AG.

    Baude FJ, Gardiner JA, & Han JC-Y (1973) Characterization of
    residues on plants following foliar spray applications of benomyl. J
    Agric Food Chem, 21: 1084-1090.

    Baude FJ, Pease HL, & Holt RF (1974) Fate of benomyl on field soil
    and turf. J Agric Food Chem, 22: 413.

    Beavers JB (1985) An acute oral toxicity study in the bobwhite quail
    with H-15,607 (MBC). St. Michaels, Maryland, Wildlife International
    Ltd (Unpublished report No. HLO 96-85, prepared for E.I. Du Pont de
    Nemours and Co., Inc.).

    Beems RB, Til HP, & van der Heijden CA (1976) Carcinogenicity study
    with carbendazim (99% MBC) in mice. The Hague, Central Institute for
    Nutrition and Food Research (TNO) (Summary Report No. R-4936,
    prepared for Hoechst AG, Frankfurt and BASF AG, Ludwigshafen).

    Boeri RL (1988a) Flow through acute toxicity of carbendazim
    technical to the eastern oyster,  Crassostrea virginica.
    Marblehead, Massachusetts, Enseco (Unpublished report No. HLO 15-89,
    prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Boeri RL (1988b) Static acute toxicity of carbendazim technical to
    the sheepshead minnow,  Cyprinodon variegatus. Marblehead,
    Massachusetts, Enseco (Unpublished report No. HLO 12-89, prepared
    for E.I. Du Pont de Nemours and Co., Inc.).

    Boeri RL (1988c) Static acute toxicity of carbendazim technical to
    the mysid,  Mysidopsis bahia. Marblehead, Massachusetts, Enseco
    (Unpublished report No. HLO 829-88, prepared for E.I. Du Pont de
    Nemours and Co., Inc.).

    Bushway RJ, Hurst HL, Kugabalasooriar J, & Perkins LB (1991)
    Determination of carbendazim in blueberries by reversed-phase high
    performance liquid chromatography. J Chromatogr, 555: 321-324.

    Canton JH (1976) The toxicity of benomyl, thiophanate-methyl, and
    BLM to four freshwater organisms. Bull Environ Contam Toxicol, 16:
    214-218.

    Carter SD, Hess RA, & Laskey JW (1987) The fungicide methyl
    2-benzimidazolecarbamate causes infertility in male Sprague-Dawley
    rats. Biol Reprod, 37(3): 709-718.

    Chiba M & Veres DF (1981) Fate of benomyl and its degradation
    compound methyl 2-benzimidazole carbamate on apple foliage. J Agric
    Food Chem, 29: 588-590.

    Christian MS, Hoberman AM, & Feussner EL (1985) Developmental
    toxicity study of carbendazim administered via gavage to New Zealand
    white rabbits. Horsham, Pennsylvania, Argus Research Laboratories,
    Inc. (Unpublished report No. HLO 515-85, prepared for E.I. Du Pont
    de Nemours and Co., Inc.).

    Clive D, Johnson KO, Spector JFS, Batson AG, & Moore-Brown MM (1979)
    Validation and characterization of the L5178Y/TK +/- mouse
    lymphoma mutagen assay system. Mutat Res, 59: 61-108.

    Cook ME & Swait AAJ (1975) Effects of some fungicide treatments on
    earthworm populations and leaf removal in apple orchards. J Hortic
    Sci, 50: 495-499.

    County Natwest Woodmac (1992) The fungicide market. London, County
    Natwest Woodmac, Agrochemical Service, pp 49-51.

    Cox DM & Puck TT (1969) Chromosomal non-disjunction: The action of
    colcemid on Chinese hamster ovary cells  in vitro. Cytogenetics, 8:
    158-169.

    Cummings AM, Harris ST, & Rehnberg GL (1990) Effects of methyl
    benzimidazole carbamate during early pregnancy in the rat. Fundam
    Appl Toxicol, 15: 528-535.

    Cummings AM, Ebron-McCoy MT, Rogers JM, Barbee BD, & Harris ST
    (1992) Developmental effects of methyl benzimidazole carbamate
    following exposure during early pregnancy. Fundam Appl Toxicol, 18:
    288-293.

    Dashiell OL (1975) Oral LD50 test in guinea pigs (Carbendazim).
    Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 846-74).

    Davidse LC (1973) Antimitotic activity of methyl benzimidazol-2-yl
    carbamate (MBC) in  Aspergillus nidulans. Pestic Biochem Physiol,
    3: 317-325.

    Davidse LC (1975) Antimitotic activity of methyl
    benzimidazol-2-ylcarbamate in fungi and its binding to cellular
    protein. In: Borgers M & de Brabander M ed. Microtubules and
    microtubule inhibitors. Amsterdam, Elsevier/North-Holland Publishing
    Company, pp 483-495.

    Davidse LC & Flach W (1977) Differential binding of methyl
    benzimidazol-2-yl carbamate to fungal tubulin as a mechanism of
    resistance to this antimitotic agent in mutant strains of
     Aspergillus nidulans. J Cell Biol, 72: 174-193.

    Davidse LC & Flach W (1978) Interaction of thiabendazole with fungal
    tubulin. Biochim Biophys Acta, 543: 82-90.

    Delatour P & Besse S (1990) Benzimidazole carbamate d'éthyle: effet
    tératogène et présence dans le lait de vache après administration de
    thiophanate. Ann Rech Vét, 21: 87-92.

    Delp CJ (1980) Coping with resistance to plant disease control
    agents. Plant Dis, 64: 652-657.

    De Brabander M, van de Veire R, Aerts F, Geuens S, & Hoebeke J
    (1976a) A new culture model facilitating rapid quantitative testing
    of mitotic spindle inhibition in mammalian cells. J Natl Cancer
    Inst, 56: 357-363.

    De Brabander M, van de Veire R, Aerts F, Brogers M, & Janssen PAJ
    (1976b) The effect of methyl [5(2-thienylcarbonyl)-1H-benzimidazol-
    2-yl carbamate (R17934; NSC 238159), a new synthetic antitumoral
    drug interfering with microtubules, on mammalian cells cultured  in
     vitro. Cancer Res, 36: 905-916.

    De Vos RH, van Dokkum W, Olthof PDA, Quirijns JK, Muys T, & van der
    Poll JM (1984) Pesticides and other chemical residues in Dutch total
    diet samples (June 1976 - July 1978). Food Chem Toxicol, 22: 11-21.

    Donaubauer HH, Schuetz E, Weigand W, & Kramer M (1982) Repeated dose
    (24 month) feeding study for determination of the carcinogenic
    effect of HOE 17411 OFAT204 (carbendazim) in mice. Frankfurt,
    Germany, Hoechst AG, Pharmaceuticals Research, Toxicology Section
    (Unpublished report).

    Donovan SD (1982) Mutagenicity evaluation in  Salmonella
     typhimurium. Newark, Delaware, E.I. Du Pont de Nemours and Co.,
    Inc., Haskell Laboratory (Unpublished report No. HLR 678-82).

    Donovan SM (1983) Mutagenicity evaluation in  Salmonella
     typhimurium. Newark, Delaware, E.I. Du Pont de Nemours and Co.,
    Inc., Haskell Laboratory (Unpublished report No. HLR 797-82).

    Dorn E, Schmidt E, Kellner HM, & Leist KH (1983) HOE 017411-14-C
    (carbendazim-14-C) metabolic fate in rats and mice, a comparison.
    Frankfurt, Germany, Hoechst AG.

    Douglas MT & Handley JW (1987) The algistatic activity of
    carbendazim technical. Huntingdon, United Kingdom, Huntingdon
    Research Centre Ltd (Unpublished report No. DPT 171(g)/871604,
    prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Du Pont (1972) Residue studies - fish: benomyl, MBC, and 2-AB.
    Wilmington, Delaware, E.I. Du Pont de Nemours and Co., Inc.
    (Unpublished report).

    Eckert J, Stauffer R, & Hoppman D (1985) Determination of MBC, 4-OH
    MBC, and 5-OH MBC in chicken eggs, tissues and feces. Bernville,
    Pennsylvania, Enviro-Bio-Tech Ltd (Unpublished report No. AMR
    260-84, prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Edwards DF (1974a) Skin absorption LD50 (carbendazim). Newark,
    Delaware, Du Pont de Nemours and Co., Inc., Haskell Laboratory
    (Unpublished report No. HLR 798-74).

    Edwards DF (1974b) Federal Hazardous Substances Act - Eye irritation
    test in rabbits (carbendazim). Newark, Delaware, E.I. Du Pont de
    Nemours and Co., Inc., Haskell Laboratory (Unpublished report No.
    HLR 799-74).

    Ellis WG, Semple JL, Hoogenboom ER, Kavlock RJ, & Zeman FJ (1987)
    Benomyl-induced craniocerebral anomalies in fetuses of adequately
    nourished and protein-deprived rats. Teratog Carcinog Mutagen, 7:
    357-375.

    Ellis WG, De Roos F, Kavlock RJ, & Zeman FJ (1988) Relationship of
    periventricular overgrowth to hydrocephalus in brains of fetal rats
    exposed to benomyl. Teratog Carcinog Mutagen, 8: 377-391.

    Evenson DP, Janca FC, & Jost LK (1987) Effects of the fungicide
    methyl-benzimidazol-2-yl carbamate (MBC) on mouse germ cells as
    determined by flow cytometry. J Toxicol Environ Health, 20: 387-399.

    Everhart LP (1979) Benlate dust exposure survey. Wilmington,
    Delaware, E.I. Du Pont de Nemours and Co., Inc. (Unpublished report
    No. B/TOX 6).

    Everhart LP & Holt RF (1982) Potential benlate fungicide exposure
    during mixer/loader operations, crop harvest and home use. J Agric
    Food Chem, 30: 222-227.

    Fahrig R & Seiler JP (1979) Dose and effect of methyl
    2-benzimidazolyl-carbamate in the "mammalian spot test", an  in vivo

    method for the detection of genetic alterations in somatic cells of
    mice. Chem-Biol Interact, 26: 115-120.

    FAO/WHO (1985a) Benomyl. In: Pesticide residues in food -
    Evaluations 1983. Rome, Food and Agriculture Organization of the
    United Nations, pp 7-46 (FAO Plant Production and Protection Paper
    61).

    FAO/WHO (1985b) Carbendazim. In: Pesticide residues in food -
    Evaluations 1983. Rome, Food and Agriculture Organization of the
    United Nations, pp 89-121 (FAO Plant Production and Protection Paper
    61).

    FAO/WHO (1988a) Benomyl. In: Pesticide residues in food -
    Evaluations 1988. Part I: Residues. Rome, Food and Agriculture
    Organization of the United Nations, pp 5-15 (FAO Plant Production
    and Protection Paper 93/1).

    FAO/WHO (1988b) Carbendazim. In: Pesticide residues in food -
    Evaluations 1988. Part I: Residues. Rome, Food and Agriculture
    Organization of the United Nations, pp 41-54 (FAO Plant Production
    and Protection Paper 93/1).

    Fielding M, Barcelo D, Helweg A, Galassi S, Torstensson L, van
    Zoonen P, Wolter R, & Angeletti G (1992) Pesticides in ground and
    drinking water. Brussels, Commission of the European Communities,
    Directorate-General for Science, Research and Development,
    Environment and Waste Recycling, 135 pp (Water Pollution Research
    Report 27).

    Fink R (1975) Eight-day dietary LC50 - Mallard ducks. Sterling,
    Virginia, Truslow Farms, Inc. (Unpublished report No. HLO 108-75,
    prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Fiscor G, Bordas S, & Steward SJ (1978) Mutagenicity testing of
    benomyl, methyl-2-benzimidazole carbamate, streptozotocin and
    N-methyl-N'-nitro-N-nitrosoguanine in  Salmonella typhimurium
     in vitro and in rodent host-mediated assays. Mutat Res, 51:
    151-164.

    Fleeker JR & Lacy HM (1977) Photolysis of methyl
    2-benzimidazole-carbamate. J Agric Food Chem, 25: 51-55.

    Ford LS (1981) Primary skin irritation and sensitization on guinea
    pigs. Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc.,
    Haskell Laboratory (Unpublished report No. HLR 729-81).

    Ford LS (1982) Acute skin absorption LD50 test on rabbits
    (carbendazim 75% wettable powder). Newark, Delaware, E.I. Du Pont de
    Nemours and Co., Inc., Haskell Laboratory (Unpublished report No.
    HLR 822-81).

    Freidman PA & Platzer EG (1978) Interaction of anthelmintic
    benzimidazoles and benzimidazoles derivatives with bovine brain
    tubulin. Biochim Biophys Acta, 544: 605-614.

    Galloway SM & Ivett JL (1986) Chemically induced aneuploidy in
    mammalian cells in culture. Mutat Res, 167: 89-105.

    Gericke D (1977) Test for mutagenicity in bacteria strains in the
    absence and presence of a liver preparation. Frankfurt, Germany,
    Hoechst AG, Laboratory for Cancer Research (Report No. A/12202).

    Gillet C & Roubaud P (1983) Prehatching survival of carp eggs after
    treatment during fertilization and early development with the
    antimitotic fungicide carbendazim. Water Res, 17: 1343-1348.

    Goldenthal EI (1978) Neurotoxicity in hens. Mattawan, Michigan,
    International Research and Development Corporation (Unpublished
    report No. HLO 27-79, prepared for E.I. Du Pont de Nemours and Co.,
    Inc.).

    Goldman JM, Rehnberg GL, Cooper RL, Gray LE Jr, Hein JF, & McElroy
    WK (1989) Effects of the benomyl metabolite, carbendazim, on the
    hypothalamic-pituitary reproductive axis in the male rat.
    Toxicology, 57(2): 173-182.

    Gooch JJ (1978) Fertility of workers potentially exposed to benomyl.
    Wilmington, Delaware, E.I. Du Pont de Nemours and Co., Inc.
    (Unpublished report No. B/TOX 7).

    Goodman NC (1974) Intraperitoneal LD50 test [in rats using
    technical carbendazim (less than 98%)]. Newark, Delaware, E.I. Du
    Pont de Nemours and Co., Inc., Haskell Laboratory (Unpublished
    report No. HLR 845-74).

    Goodman NC & Sherman H (1975) Oral LD50 tests (fasted male and
    female rats). Newark, Delaware, E.I. Du Pont de Nemours and Co.,
    Inc., Haskell Laboratory (Unpublished report No. HLR 847-74).

    Grandizio AM & Sarver JW (1987) Acute oral toxicity study with
    INE-965-261 (Benlate C) in male and female rats. Newark, Delaware,
    E.I. Du Pont de Nemours and Co., Inc., Haskell Laboratory
    (Unpublished report No. HLR 358-87).

    Gray LE, Ostby J, Sigmon R, Ferrell J, Rehnberg G, Linder R, Cooper
    R, Goldman J, & Laskey J (1988) The development of a protocol to
    assess reproductive effects of toxicants in the rat. Reprod Toxicol,
    2: 281-287.

    Gray LE, Ostby J, Linder R, Goldman J, Rehnberg G, & Cooper R (1990)
    Carbendazim-induced alterations of reproductive development and
    function in the rat and hamster. Fundam Appl Toxicol, 15: 281-297.

    Guengerich FP (1981) Enzyme induction with Du Pont compounds
    H11,201-02 and H10,962-02. Nashville, Tennessee, Vanderbilt
    University, School of Medicine (Unpublished report No. HLO-850-81,
    prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Gupta VK & Sharma SD (1989) Degradation of carbendazim in soil by
    microorganisms. Indian J Agric Sci, 59: 21-24.

    Gustafson DI (1989) Groundwater ubiquity score: A simple method for
    assessing pesticide leachability. Environ Toxicol Chem, 8: 339-357.

    Hammerschlag RS & Sisler HD (1973) Benomyl and
    methyl-2-benzimidazole (MBC): biochemical, cytological, and chemical
    aspects of toxicity to  Ustilage maydis and  Saccharomyces
     cerevesiae. Pestic Biochem Physiol, 3: 42-54.

    Han JC-Y (1983a) Characterization of residues in bean plants
    following foliar spray applications with methyl
    2-14C-benzimidazolecarbamate (MBC). Wilmington, Delaware, E.I. Du
    Pont de Nemours and Co., Inc. (Unpublished report No. MBC/ME-4).

    Han JC-Y (1983b) Anaerobic soil metabolism of 2-14C-benomyl and
    methyl 2-14C-benzimidazolecarbamate. Wilmington, Delaware, E.I. Du
    Pont de Nemours and Co., Inc. (Unpublished report No. B/ME-44).

    Heinemann JM (1971) Acute static fish (rainbow trout) toxicity study
    - freshwater (MBC). Vienna, Virginia, Hazelton Laboratories
    (Unpublished report No. HLO-150-71, prepared for E.I. Du Pont de
    Nemours and Co., Inc.).

    Helweg A (1977) Degradation and adsorption of carbendazim and
    2-aminobenzimidazole in soil. Pestic Sci, 8: 71-78.

    Helweg A (1979) Influence of temperature, humidity, and inoculation
    on the degradation of 14C-labelled 2-aminobenzimidazole in soil.
    Water Air Soil Pollut, 12: 275-281.

    Helweg A (1985) Side effects caused by pesticide combinations. In:
    Jensen V, Kjoller A, & Sorensen LH ed. Proceedings of the FEMS
    Symposium on Microbial Communities in Soil. Amsterdam, Oxford, New
    York, Elsevier Science Publishers, pp 385-395.

    Hill EF & Camardese MB (1986) Lethal toxicities of environmental
    contaminants and pesticides to Coturnix. Washington, DC, US
    Department of the Interior, Fish and Wildlife Service (Fish and
    Wildlife Technical Report No. 2).

    Hinckle L (1981) Oral LD50 test in rats - EPA proposed guidelines.
    Newark, Delaware, E.I. du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 769-81).

    Hoechst (1974) Mouse dominant lethal study on MBC. Frankfurt,
    Germany, Hoechst AG.

    Hofer I, Beck T, & Wallnöfer P (1971) [The influence of the
    fungicide benomyl on soil microflora.] Z Pflanzenkr Pflanzenschutz,
    78: 399-405 (in German).

    Holden HE, Crider PA, & Wahrenburg MG (1980) Mitotic arrest by
    benzimidazole analogs in human lymphocyte cultures. Environ Mutat,
    2: 67-73.

    Hughes DL (1984) Residue study of the fungicide MBC in lactating
    dairy cattle. Madison, Wisconsin, Hazelton Laboratories America,
    Inc. (Unpublished report No. AMR 429-85, prepared for E.I. Du Pont
    de Nemours and Co., Inc.).

    Hutton DG (1988) Static acute 48-hours EC50 of carbamic acid,
    1H-benzimidazol-2-yl-, methyl ester to fed  Daphnia magna. Newark,
    Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell Laboratory
    (Unpublished report No. HLR 638-88).

    Hutton DG, Kasprzak DJ, & Priester TM (1984) Laboratory studies of
    [2-14C] carbendazim bioconcentration in bluegill sunfish. Newark,
    Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell Laboratory
    (Unpublished report No. HLR 428-84).

    Hutton DG, Lieder PH, & Grapel GJ (1986) Chronic toxicity of
    carbamic acid, 1H-benzimidazol-2-yl-, methyl ester to  Daphnia
     magna. Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc.,
    Haskell Laboratory (Unpublished report No. HLR 241-86).

    ILO (1991) Occupational exposure limits for airborne toxic
    substances, 3rd ed. Geneva, International Labour Office, 455 pp
    (Occupational Safety and Health Series No. 37).

    Ireland CM, Gull K, Gutteridge WE, & Pogson CI (1979) The
    interaction of benzimidazole carbamates with mammalian microtubule
    protein. Biochem Pharmacol, 28: 2680-2682.

    Ivett JL (1984) Mutagenicity evaluation of H#15,152 in an  in vitro
    sister chromatid exchange assay in Chinese hamster ovary (CHO)
    cells. Kensington, Maryland, Litton Bionetics, Inc. (Unpublished
    report No. HLO 254-84, prepared for E.I. Du Pont de Nemours and Co.,
    Inc.).

    Janardhan A, Sattur PB, & Sisodia P (1984) Teratology of methyl
    benzimidazole carbamate in rats and rabbits. Bull Environ Contam
    Toxicol, 33(3): 257-263.

    Janardhan A, Rao AB, & Sisodia P (1987) Sub-chronic toxicity of
    methyl benzimidazole carbamate in rats. Bull Environ Contam Toxicol,
    38(5): 890-898.

    Jansz GF & Pomerantz DK (1985) The effect of prenatal treatment with
    busulfan on  in vitro androgen production by testes from rats of
    various ages. Can J Physiol Pharmacol, 63: 1155-1158.

    Johnson JD (1988) Determination of the plateau level of bound
    [phenyl(U)-14C]carbendazim residues in goat liver. Columbus, Ohio,
    Battelle Columbus Division (Unpublished report No. AMR-779-87,
    prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Jotz MM (1980) An evaluation of mutagenic potential of benomyl
    employing the L5178Y TK+/- mouse lymphoma assay (SRI Project No.
    LSU 7558). Menlo Park, California, SRI International (Unpublished
    report prepared for the US Environmental Protection Agency).

    Keogh RG & Whitehead PH (1975) Observations on some effects of
    pasture spraying with benomyl and carbendazim on earthworm activity
    and litter removal from pasture. NZ J Exp Agric, 3: 103-104.

    Khan S, Khan NN, & Khan FA (1987) The influence of bavistin and
    calixin on carbon dioxide-evolution and the major nutrient status
    (nitrogen, phosphorus, potassium) of the soil. Environ Pollut,
    47(2): 115-122.

    Kirkland JJ (1973) Method for high-speed liquid chromatographic
    analysis of benomyl and/or metabolite residue in cow milk, urine,
    feces and tissues. J Agric Food Chem, 21: 171-177.

    Kirkland JJ, Holt RF, & Pease HL (1973) Determination of benomyl
    residues in soils and plant tissues by high-speed cation exchange
    liquid chromatography. J Agric Food Chem, 21: 368-371.

    Koeter HBWM (1975a) Effect of HOE 17411F (=BAS 3460F) on pregnancy
    of the rat. The Hague, Central Institute of Nutrition and Food
    Research (TNO) (Unpublished report No. R-4726, prepared for Hoechst
    AG, Frankfurt and BASF AG, Ludwigshafen).

    Koeter HBWM (1975b) Effect of HOE 17411F (=BAS 3460F) on pregnancy
    of the New Zealand white rabbit. The Hague, Central Institute for
    Nutrition and Food Research (TNO) (Unpublished report No. R-4881,
    prepared for Hoechst AG, Frankfurt and BASF AG, Ludwigshafen).

    Kramer M & Weigand W (1971) (HOE 17411 O F) Toxicological
    examination. Frankfurt, Germany, Hoechst AG, Pharmaceuticals
    Research, Toxicology Section (Unpublished report No. A-00936).

    Krechniak J & Klosowska B (1986) The fate of 14C-carbendazim in
    rat. Xenobiotica, 16(9): 809-815.

    Lamb MJ & Lilly LJ (1980) An investigation of some genetic
    toxicological effects of the fungicide benomyl. Toxicology, 17:
    83-95.

    Litton (1981) Evaluation of HOE 17411 O F AT204 in the primary rat
    hepatocyte unscheduled DNA synthesis assay (LBI Project No. 21001).
    Kensington, Maryland, Litton Bionetics, Inc. (Unpublished report
    prepared for Hoechst AG, Frankfurt).

    Lofs-Holmin A (1981) Influence in field experiments of benomyl and
    carbendazim on earthworms ( Lumbricidae) in relation to soil
    texture. Swed J Agric Res, 11: 141-147.

    Lofs-Holmin A (1982) Influence of routine pesticide spraying on
    earthworms ( Lumbricidea) in field experiments with winter wheat.
    Swed J Agric Res, 12: 121-124.

    Marsh BH & Arthur MF (1989) Aerobic metabolism of
    [phenyl(U)-14C]benomyl in keyport silt loam. Columbus, Ohio,
    Battelle Memorial Institute (Unpublished report No. AMR 1112-88,
    prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Martin DA, Henry JE, & Brock WJ (1987) Closed-patch repeated insult
    dermal sensitization study (Buehler Method) with Benlate C fungicide
    in guinea-pigs. Newark, Delaware, E.I. Du Pont de Nemours and Co.,
    Inc., Haskell Laboratory (Unpublished report No. HLR 510-87).

    Marvin Ch, Birndle ID, Hall CD, & Chiba M (1991) Rapid on-line
    precolumn high performance liquid chromatographic method for the
    determination of benomyl, carbendazim and aldicarb species in
    drinking water. J Chromatogr, 555: 147-154.

    Mayer FL & Ellersieck MR (1986) Manual of acute toxicity:
    Interpretation and data base for 410 chemicals and 66 species of
    freshwater animals. Washington, DC, US Department of the Interior,
    Fish and Wildlife Service, pp 45-46 (Resource Publication No. 160).

    Mazur AR & Hughes TD (1975) Nitrogen transformations in soil as
    affected by the fungicides benomyl, dyrene and maneb. Agron J, 67:
    755-758.

    Meade AB (1984) Acute contact LD50 toxicity study in honey bees
    ( Apis mellifera L.) with INE965-212 (MBC). Wilmington, Delaware,
    E.I. Du Pont de Nemours and Co., Inc. (Unpublished report No.
    ABM-84-5).

    Mohr U (1977) Review of liver sections from mice and rats fed with
    carbendazim. Hannover, Germany, Medical School, Department of

    Experimental Pathology (Unpublished report No. MBC/TOX 6, prepared
    for Hoechst AG, Frankfurt and BASF AG, Ludwigshafen).

    Monson KD (1985) Metabolism of [2-14C]-carbendazim in the
    lactating dairy cow. Wilmington, Delaware, E.I. Du Pont de Nemours
    and Co., Inc. (Unpublished report No. AMR 248-84).

    Monson KD (1986) Metabolism of [2-14C]-carbendazim in laying hens.
    Wilmington, Delaware, E.I. Du Pont de Nemours and Co., Inc.
    (Unpublished report No. AMR 264-84).

    Monson KD (1990) Metabolism of [phenyl(U)-14C]carbendazim in rats.
    Wilmington, Delaware, E.I. Du Pont de Nemours and Co., Inc.
    (Unpublished report No. AMR-1141-88).

    Monson KD (1991) Release and characterization of bound benomyl and
    carbendazim metabolites in animal tissues via Raney nickel
    desulfurization and acid dehydration. J Agric Food Chem, 39:
    1808-1811.

    Nakai M, Hess RA, Moore BJ, Guttroff RF, Strader LF, & Linder RE
    (1992) Acute and long-term effects of a single dose of the fungicide
    carbendazim (methyl 2-benzimidazole carbamate) on the male
    reproductive system in the rat. J Androl, 13: 507-518.

    Nash SD & Ferenz R (1982) Inhalation median lethal concentration
    (LC50 in rats -EPA protocol (carbendazim 75% wettable powder).
    Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 365-82).

    Newsome WH & Collins PG (1987) Enzyme-linked immunosorbent assay of
    benomyl and thiabendazole in some foods. J Assoc Off Anal Chem, 70:
    1025-1027.

    Newsome WH & Shields JB (1981) A radioimmunoassay for benomyl and
    methyl 2-benzi midazolecarbamate on food. J Agric Food Chem, 29:
    220-222.

    Nishiuchi Y & Yoshida K (1974) Toxicity of new agricultural
    chemicals to tadpoles. Bull Agric Chem Insp Stn, 14: 66-68.

    Osgood C, Zimmering S, & Mason JM (1991) Aneuploidy in Drosophila.
    II. Further validation of the FIX and ZESTE genetic test systems
    employing female  Drosophila melanogaster. Mutat Res, 259: 147-163.

    Palawski DU & Knowles CO (1986) Toxicological studies of benomyl and
    carbendazim in rainbow trout, channel catfish and bluegills. Environ
    Toxicol Chem, 5: 1039-1046.

    Pandita TK (1988) Assessment of the mutagenic potential of a
    fungicide Bavistin using multiple assays. Mutat Res, 204: 627-643.

    Parsons DW & Witt JM (1988) Pesticides in groundwater in the United
    States of America: A report of a 1988 survey of State lead agencies.
    Corvallis, Oregon, Oregon State University Extension Service.

    Peeples JL (1974) Microbial activity in benomyl-treated soil.
    Phytopathology, 64: 857-860.

    Perreault SD, Jeffay S, Poss P, & Laskey JW (1992) Use of the
    fungicide carbendazim as a model compound to determine the impact of
    acute chemical exposure during oocyte maturation and fertilization
    on pregnancy outcome in the hamster. Toxicol Appl Pharmacol, 114:
    225-231.

    Priester TM (1984) Hydrolysis of carbendazim [2-14C]. Newark,
    Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell Laboratory
    (Unpublished report No. AMR 265-84).

    Purser D (1987) Carbendazim: behaviour in water. Harrogate, North
    Yorkshire, United Kingdom, Hazelton Laboratories (Unpublished report
    No. 5220-269/12, prepared for E.I. Du Pont de Nemours and Co.,
    Inc.).

    Ramakrishna C, Gowda TKS, & Sethunathan N (1979) Effect of benomyl
    and its hydrolysis products, MBC and AB on nitrification in flooded
    soil. Bull Environ Contam Toxicol, 21: 328-333.

    Rashid MA & Mumma RO (1986) Screening pesticides for their
    availability to damage bacterial DNA. J Environ Sci Health, B21:
    319-334.

    Raw F (1962) Studies of earthworm populations in orchards. Ann Appl
    Biol, 50: 389-404.

    Rehnberg GL, Cooper RL, Goldman JM, Gray LE, Hein JF, & McElroy WK
    (1989) Serum and testicular testosterone and androgen binding
    protein profiles following subchronic treatment with carbendazim.
    Toxicol Appl Pharmacol, 101: 55-61.

    Reuzel PGJ, Hendriksen CFM, & Til HP (1976) Long-term (two-year)
    toxicity study with carbendazim in beagle dogs. The Hague, Central
    Institute for Nutrition and Food Research (TNO) (Unpublished report
    prepared for BASF AG, Ludwigshafen and Hoechst AG, Frankfurt).

    Rhodes RC (1987) Greenhouse crop-rotation study with
    [2-14C]carbendazim. Wilmington, Delaware, E.I. Du Pont de Nemours
    and Co., Inc. (Unpublished report No. AMR-495-86).

    Rhodes RC & Long JD (1983) Run-off and leaching studies with methyl
    2-14C-benzimidazolecarbamate on soil. Wilmington, Delaware, E.I.
    Du Pont de Nemours and Co., Inc. (Unpublished report No. MBC/ME-9).

    Rhodes RC, Pease HL, & Holt RF (1983) Greenhouse studies on crop
    uptake of MBC and 2-AB from soil. Wilmington, Delaware, E.I. Du Pont
    de Nemours and Co., Inc. (Unpublished Report No. MBC/ME-5).

    Roberts BL & Dorough HW (1984) Relative toxicities on chemicals to
    the earthworm  Eisenia foetida. Environ Toxicol Chem, 3: 67-78.

    Russel LD, Ettlin RA, Sinha Hikim AP, & Clegg ER (1990) Histological
    and histopathological evaluation of the testis. Clearwater, Florida,
    Cache River Press.

    Russell JF (1977) Mutagenicity evaluation of 2-benzimidazolecarbamic
    acid, 5-hydroxy-, methyl in  Salmonella typhimurium. Newark,
    Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell Laboratory
    (Unpublished report).

    Russell JF (1983) Mutagenicity evaluation in  Salmonella
     typhimurium. Newark, Delaware, E.I. Du Pont de Nemours and Co.,
    Inc., Haskell Laboratory (Unpublished report No. HLR 179-83).

    Sarver JW (1975) Acute inhalation toxicity - one hour head only
    (carbendazim). Newark, Delaware, E.I. Du Pont de Nemours and Co.,
    Inc., Haskell Laboratory (Unpublished report No. HLR 58-75).

    Scholz J & Weigand W (1972) Carbendazim (HOE 17411 O F, batch
    496/I). Toxicological examination. Frankfurt, Germany, Hoechst AG,
    Pharmaceuticals Research, Toxicology Section (Unpublished report No.
    A-00935).

    Seiler JP (1976) The mutagenicity of benzimidazole and benzimidazole
    derivatives. VI. Cytogenetic effects of benzimidazole derivatives in
    the bone marrow of the mouse and the Chinese hamster. Mutat Res, 40:
    339-348.

    Seiler JP (1977) Apparent and real thresholds: A study on two
    mutagens. In: Scott D, Bridges BA, & Sobels FH ed. Progress in
    genetic toxicology. Amsterdam, Elsevier/North-Holland Biomedical
    Press, pp 233-238.

    Sheir-Neiss F, Nardi RV, Gealt A, & Morris NR (1976) Tubulin-like
    protein from  Aspergillus nidulans. Biochem Biophys Res Commun, 69:
    285-290.

    Sherman H (1965) Acute oral test. Newark, Delaware, E.I. Du Pont de
    Nemours and Co., Inc., Haskell Laboratory (Unpublished report No.
    HLR 125-65).

    Sherman H (1968) Ninety-day feeding study in rats using a wettable
    powder formulation (70% MBC). Newark, Delaware, E.I. Du Pont de
    Nemours and Co., Inc., Haskell Laboratory (Unpublished report No.
    HLR 95-68).

    Sherman H (1970) Three-month feeding study in dogs using a wettable
    powder formulation (50% MBC). Newark, Delaware, E.I. Du Pont de
    Nemours and Co., Inc., Haskell Laboratory (Unpublished report No.
    HLR 283-70).

    Sherman H (1972) Long-term feeding studies in rats and dogs with
    2-benzimadazole carbamic acid, methyl ester (INE-965) (50% and 70%
    MBC wettable powder formulations). Parts I and II. Newark, Delaware,
    E.I. Du Pont de Nemours and Co., Inc., Haskell Laboratory
    (Unpublished report No. HLR 195-72).

    Sherman H & Krauss WC (1966) Acute oral test (carbendazim). Newark,
    Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell Laboratory
    (Unpublished report No. HLR 99-66).

    Sheu CW, Lee JK, Arras CA, Jones RL, & Lavappa KS (1990) The
    feasibility of using Chinese hamster as an animal model for
    aneuploidy. Environ Mol Mutagen, 16: 320-323.

    Shirasu Y, Moriya M, & Kato K (1977) Mutagenicity testing on
    fungicide 1991 in microbial systems. Tokyo, Institute of
    Environmental Toxicology, Kodaira Laboratories (Unpublished report
    prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Shukla Y, Antony M, & Mehrotra NK (1989) Studies on g-glutamyl
    transpeptidase in rodents exposed to benomyl. Bull Environ Contam
    Toxicol, 42: 301-306.

    Siebert D, Zimmermann FK, & Lemperle E (1970) Genetic effects of
    fungicides. Mutat Res, 10: 533-543.

    Speakman JB & Nirenberg HI (1981) Mutagenicity of methyl
    benzimidazole-2-yl carbamate (MBC) towards  Aspergillus nidulans
    (Eidam) Winter and  Cladosporium cucumerinum Ellis and Arth. Mutat
    Res, 88: 45-51.

    Stadler JC (1986) One-year feeding study in dogs with carbendazim.
    Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 291-86).

    Staub T & Sozzi D (1984) Fungicide resistance: A continuing
    challenge. Plant Dis, 68: 1026-1031.

    Stringer A & Lyons C (1974) The effect of benomyl and
    thiophanate-methyl on earthworm populations in apple orchards.
    Pestic Sci, 5: 189-196.

    Stringer A & Wright MA (1973) The effect of benomyl and some related
    compounds on  Lumbricus terrestris and other earthworms. Pestic
    Sci, 4: 165-170.

    Styles JA & Garner R (1974) Benzimidazolecarbamate methyl ester -
    evaluation of its effects  in vivo and  in vitro. Mutat Res, 26:
    177-187. 

    Til HP, van den Muelen HC, Feron VJ, Seinen W, & de Groot
    AP (1972) Sub-chronic (90-day) toxicity study with W17411 in beagle
    dogs. The Hague, Central Institute for Nutrition and Food Research
    (TNO) (Unpublished report No. R-3920, prepared for Hoechst AG,
    Frankfurt).

    Til HP, Koellen C, & van der Heijden CA (1976a) Combined chronic
    toxicity and carcinogenicity study with carbendazim in rats. The
    Hague, Central Institute for Nutrition and Food Research (TNO)
    (Unpublished report prepared for BASF AG, Ludwigshafen and Hoechst
    AG, Frankfurt).

    Til HP, Koeter HBWM, & van der Heijden CA (1976b) Multigeneration
    study with carbendazim in rats. The Hague, Central Institute for
    Nutrition and Food Research (TNO) (Unpublished report No. R-5024,
    prepared for Hoechst AG, Frankfurt).

    Til HP, Beems RB, & de Groot AP (1981) Determination of the acute
    oral toxicity of carbendazim in mice. The Hague, Central Institute
    for Nutrition and Food Research (TNO) (Unpublished report No.
    A-21604, prepared for BASF AG, Ludwigshafen).

    Tong C (198la) Hepatocyte primary culture/DNA repair assay on
    compound l1, 201-01 (MBC) using mouse hepatocytes in culture.
    Valhalla, New York, Naylor Dana Institute (Unpublished report No.
    HLO 743-81, prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Tong C (198lb) Hepatocyte primary culture/DNA repair assay on
    compound 11,201-01 (MBC) using rat hepatocytes in culture. Valhalla,
    New York, Naylor Dana Institute (Unpublished report No. HLO 744-81,
    prepared for E.I. Du Pont de Nemours and Co., Inc.).

    Torstensson L & Wessen B (1984) Interactions between the fungicide
    benomyl and soil microorganisms. Soil Biol Biochem, 16: 445-452.

    Van Faassen HG (1974) Effect of the fungicide benomyl on some
    metabolic processes and on numbers of bacteria and actinomycetes in
    the soil. Soil Biol Biochem, 6: 131-133.

    Van Gestel CAM (1992) Validation of earthworm toxicity tests by
    comparison with field studies: A review of benomyl, carbendazim,
    carbofuran, and carbaryl. Ecotoxicol Environ Saf, 23: 221-236.

    Van Gestel CAM, Dirven-van Breeman EM, Baerselman R, Emans HJB,
    Janssen JAM, Postuma R, & van Vliet PJM (1992) Comparison of
    sublethal and lethal criteria for nine different chemicals in
    standardized toxicity tests using the earthworm  Eisenia andrei.
    Ecotoxicol Environ Saf, 23: 206-220.

    Vick DA & Brock WJ (1987a) Primary dermal irritation study with
    Benlate C fungicide in rabbits. Newark, Delaware, E.I. Du Pont de
    Nemours and Co., Inc., Haskell Laboratory (Unpublished report No.
    HLR 299-87).

    Vick DA & Brock WJ (1987b) Acute dermal toxicity study of Benlate C
    fungicide in rabbits. Newark, Delaware, E.I. Du Pont de Nemours and
    Co., Inc., Haskell Laboratory (Unpublished report No. HLR 303-87).

    Vick DA & Valentine R (1987) Primary eye irritation study with
    Benlate C fungicide in rabbits. Newark, Delaware, E.I. Du Pont de
    Nemours and Co., Inc., Haskell Laboratory (Unpublished report No.
    HLR 287-87).

    Vonk JW, Adema OMM, & Barug D (1986) Comparison of the effects of
    several chemicals on microorganisms, higher plants and earthworms.
    In: Assink JW & van den Brink WG ed. Contaminated soil. Dordrecht,
    Boston, Lancaster, Martinus Nijhoff Publishers, p 191.

    Wainwright M & Pugh GJF (1974) The effect of fungicides on certain
    chemical and microbial properties of soils. Soil Biol Biochem, 6:
    263-267.

    Wallin M, Friden B, & Billger M (1989) Studies of the interaction of
    chemicals with microtubule assembly  in vitro can be used as an
    assay for detection of cytotoxic chemicals and possible inducers of
    aneuploidy. Mutat Res, 201: 303-311.

    Waterer JC (1980) Chinese hamster ovary cell assay for mutagenicity.
    Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 660-88).

    Weeks RE & Hedrick HG (1975) Influence of a systemic fungicide on
    oxygen uptake by soil microorganisms. Soil Sci, 119: 280-284.

    Wetzel JW & Hutton DG (1984) 96-Hour LC50 to bluegill sunfish.
    Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 401-84).

    Whittaker SG, Moser SF, Maloney DH, Piegorsch WW, Resnick MA, &
    Fogel S (1990) The detection of mitotic and meiotic chromosome gain
    in the yeast  Saccharomyces cerevisiae: Effects of methyl
    benzimidazol-2-yl carbamate, methyl methanesulfonate, ethyl
    methanesulfonate, dimethyl sulfoxide, propionitrile and
    cyclophosphamide monohydrate. Mutat Res, 242: 231-258.

    WHO (1993) Environmental Health Criteria 148: Benomyl. Geneva, World
    Health Organization.

    Wood CK (1982) Long-term feeding study with 2-benzimidazole-
    carbamate, methyl ester (< 99% MBC, INE-965) in mice. Parts I and
    II. Newark, Delaware, E.I. Du Pont de Nemours and Co., Inc., Haskell
    Laboratory (Unpublished report No. HLR 70-82).

    Yarden O, Aharonson N, & Katan J (1987) Accelerated microbial
    degradation of methyl benzimidizol-2-ylcarbamate in soil and its
    control. Soil Biol Biochem, 19(6): 735-739.

    RESUME ET CONCLUSIONS

    1.  Résumé

    1.1  Identité, propriétés physiques et chimiques et méthodes d'analyse

         Le carbendazime, un solide cristallin blanc, est un fongicide
    endothérapique qui appartient à la famille du benzimidazole. Son
    point de fusion est d'environ 250 °C et sa tension de vapeur est <
    1 x 10-7 Pa (< 1 x 10-9 mbar) à 20 °C. Le carbendazime est
    pratiquement insoluble dans l'eau, sa solubilité n'étant que de 8
    mg/litre à pH 7 et à 20 °C. Il est stable dans les conditions
    normales de stockage.

         L'analyse des résidus de même que celle des prélèvements
    effectués dans l'environnement comportent une extraction au moyen
    d'un solvant organique et une purification de l'extrait par partage
    liquide-liquide. Le dosage de ces résidus peut s'effectuer par
    chromatographie en phase liquide à haute performance ou par titrage
    immunologique.

    1.2  Sources d'exposition humaine et environnementale

         Le carbendazime est, parmi les fongicides de la famille du
    benzimidazole, celui qui est le plus largement utilisé. Il est
    présenté sous forme de dispersion ou de suspension aqueuse, de
    granulés fluants dispersables dans l'eau et de poudre mouillable.

    1.3  Transport, distribution et transformation dans l'environnement

         Le carbendazime est d'ailleurs le produit de transformation
    dans l'environnement du bénomyl, un autre fongicide
    benzimidazolique; la réaction est rapide avec une demi-vie
    respective de 2 et 19 heures dans l'eau et le sol. On peut donc
    utiliser les résultats des études sur le bénomyl ou sur le
    carbendazime pour l'évaluation des effets sur l'environnement.

         Dans l'environnement, le carbendazime se décompose avec une
    demi-vie de 6 à 12 mois sur le sol nu, de 3 à 6 mois sur le gazon et
    de 2 à 25 mois dans l'eau en aérobiose et en anaérobiose,
    respectivement. Le carbendazime est principalement décomposé par les
    microorganismes. Le 2-aminobenzimidazole (2-AB) en est l'un des
    principaux produits de dégradation et il est à son tour décomposé
    par les microorganismes. Lors de la décomposition du bénomyl marqué
    au 14C sur le noyau phényle, on a constaté que 9% seulement du
    carbone-14 était éliminé sous forme de CO2 en une année
    d'incubation. Le carbone-14 restant était principalement récupéré
    sous forme de carbendazime et de résidus liés. L'étude de la
    destinée d'un éventuel produit de dégradation (1,2-diaminobenzène)
    pourrait peut-être permettre de mieux définir la voie de dégradation
    des fongicides benzimidazoliques dans l'environnement.

         Des études effectuées sur le terrain ou sur colonne ont montré
    que le carbendazime restait dans les couches superficielles du sol.
    On n'a pas mesuré l'adsorption du carbendazime dans le sol, mais on
    pense qu'elle doit être aussi forte que dans le cas du bénomyl, avec
    des valeurs de Koc allant de 1000 à 3600. Les valeurs de log Kow
    sont respectivement de 1,36 et de 1,49 pour le bénomyl et le
    carbendazime.

         Un modèle de criblage basé sur les données d'adsorption et de
    persistance n'a pas révélé de risque de lessivage. Cette observation
    est corroborée par des analyses d'eau de pluie effectuées aux
    Etats-Unis, analyses qui n'ont pas permis de déceler ce composé dans
    l'un quelconque des 212 puits étudiés (la limite de détection n'a
    pas été précisée). On estime que le bénomyl et le carbendazime
    entraînés par ruissellement correspondent uniquement à la fraction
    adsorbée aux particules de sol; d'ailleurs ces composés sont sans
    doute fortement adsorbés aux sédiments présents dans l'environnement
    aquatique.

         Le carbendazime est hydrolysé en 2-AB. Ce produit en constitue
    également le principal métabolite dans le sol et les végétaux.

         Chez l'animal, le carbendazime est métabolisé en
    (5-hydroxy-1H-benzimidazole-2-yl)-carbamate (5-HBC) et autres
    métabolites polaires, qui sont rapidement excrétés. On n'a pas
    observé d'accumulation de carbendazime dans aucun système
    biologique.

    1.4  Concentrations dans l'environnement et exposition humaine

         Il ne semble pas qu'il existe de données résultant d'une
    surveillance du carbendazime dans l'environnement. Toutefois on peut
    récapituler comme suit les données d'études portant sur la destinée
    écologique de ce produit.

         Comme le bénomyl et le carbendazime restent stable pendant des
    semaines sur les végétaux, ils peuvent être ingérés par des
    organismes qui se nourrissent de feuilles mortes. Des résidus de
    carbendazime peuvent subsister jusqu'à 3 ans dans le sol et les
    sédiments. Toutefois la forte adsorption du carbendazime aux
    particules de sol et de sédiments réduit l'exposition des organismes
    terrestres et aquatiques.

         Ce sont les résidus de bénomyl et de carbendazime présents sur
    les cultures vivrières qui constituent la principale source
    d'exposition de la population humaine dans son ensemble. L'analyse
    de l'exposition par voie alimentaire qui a été effectuée aux
    Etats-Unis (bénomyl plus carbendazime) et aux Pays-Bas (carbendazime
    seul) a montré que la quantité moyenne ingérée était
    vraisemblablement de l'ordre d'une dixième de la dose journalière

    acceptable (DJA) qui est, pour le bénomyl, de 0.02 mg/kg de poids
    corporel et pour le carbendazime, de 0,01 mg/kg de poids corporel.

         L'exposition professionnelle au cours de la production est
    inférieure à la valeur-seuil établie pour le bénomyl. Les ouvriers
    agricoles qui préparent les mélanges, effectuent le remplissage ou
    retournent dans les champs traités par du bénomyl ou du
    carbendazime, courent un risque d'exposition cutanée correspondant à
    quelques milligrammes de bénomyl par heure. Le port de dispositifs
    de protection permettrait de réduire encore cette exposition. En
    outre, étant donné que l'absorption percutanée est vraisemblablement
    faible, il est très peu probable que le carbendazime puisse avoir
    des effets toxiques généraux sur les populations humaines en étant
    absorbé par cette voie.

    1.5  Cinétique et métabolisme

         Le carbendazime est bien absorbé (à hauteur de 80 à 85%) après
    ingestion mais il l'est beaucoup moins après exposition par voie
    cutanée. Une fois absorbé, le carbendazime donne naissance dans
    l'organisme à de nombreux métabolites. Les principaux d'entre eux
    sont le 5-HBC et les 5,6-HOBC-N-oxydes. Le 5,6-DHBC-S et le
    5,6-DHBC-G constituent des métabolites mineurs.

         D'après la distribution tissulaire du carbendazime, il n'y a
    pas de bioconcentration. Chez le rat, la concentration la plus
    élevée après administration par voie orale (< 1% de la dose), a été
    constatée dans le foie. Le produit se retrouvait sous forme de
    carbendazime dans les mitochondries, de 5-HBC dans le cytosol et de
    2-AB dans les microsomes. On a également retrouvé le carbendazime et
    ses métabolites dans les reins de poulets et de vaches après
    exposition, mais il ne se trouvait pas dans les autres tissus en
    quantités appréciables. Après administration de carbendazime à des
    vaches laitières, on a retrouvé de petites quantités de 5-HBC et de
    4-HBC dans le lait.

         Soixante-douze heures après avoir été administré par voie orale
    à des rats, le carbendazime était excrété dans leurs urines.

         Chez les rats et les souris, de fortes doses de carbendazime
    administrées, soit mêlées à la nourriture, soit par gavage, ont eu
    un effet sur certaines enzymes microsomiques du foie. Ainsi il y a
    eu induction de la styrène-7,8-hydrolase et de l'époxyde-hydrolase
    mais réduction de l'activité de la 7-hydroxycoumarine-O-déséthylase.
    On a également constaté une induction de l'activité de la
    glutation-S-transférase du cytosol.

    1.6  Effets sur les mammifères de laboratoire et sur les systèmes
         d'épreuve in vitro

    1.6.1  Exposition unique

         Le carbendazime présente une faible toxicité aiguë. Les valeurs
    de la DL50 vont de > 2000 à 15 000 mg/kg chez toutes sortes
    d'animaux d'expérience exposés par diverses voies. Toutefois on n'a
    pas noté, après exposition unique, d'effets nocifs sensibles sur la
    reproduction (voir Section 1.6.5).

    1.6.2  Exposition de brève durée

         Administré en mélange à la nourriture pendant des périodes
    allant jusqu'à 90 jours, le carbendazime a entraîné une légère
    modification du poids du foie chez des rattes qui en avaient reçu
    une dose quotidienne de 360 mg/kg de poids corporel. Une étude de 90
    jours au cours de laquelle du carbendazime a été administré par
    gavage à des rats, a permis de fixer à 16 mg/kg/jour la dose sans
    effets observables, basée sur l'hépatotoxicité. Les études
    d'alimentation de courte durée effectuées sur des chiens se sont
    révélées insuffisantes pour l'établissement d'une dose sans effets
    observables. Une étude de 10 jours, au cours de laquelle de lapins
    ont été exposés au carbendazime par voir cutanée n'a pas permis de
    mettre en évidence une toxicité générale à la seule dose étudiée
    (200 mg/kg).

    1.6.3  Irritation et sensibilisation au niveau de la peau et des
           yeux

         L'application du produit sur l'épiderme de lapins ou de cobayes
    n'a produit aucune irritation ni sensibilisation de la peau. Chez le
    lapin, l'instillation oculaire n'a produit qu'une irritation légère
    à modérée de la conjonctive.

    1.6.4  Exposition de longue durée

         A l'issue d'une étude d'alimentation où des rats mâles et
    femelles avaient reçu 2500 mg de carbendazime/kg de nourriture, on a
    constaté une réduction du nombre des érythrocytes ainsi que du taux
    d'hémoglobine et de l'hématocrite. Aucun effet toxique sur le foie
    n'a été constaté. Parmi les rats mâles qui avaient reçu du
    carbendazime à raison de 2500 mg ou davantage/kg de nourriture, on
    notait une augmentation peu importante du nombre de cas d'atrophie
    testiculaire diffuse et de prostatite. Chez le rat, la dose sans
    effets observables est de 500 mg/kg de nourriture. Des chiens qui
    avaient reçu pendant une année ou davantage une nourriture contenant
    500 mg de carbendazime/kg, ont présenté une élévation du taux de
    cholestérol sérique et de l'activité de la phosphatase alcaline
    accompagnée d'autres indices d'une hépatotoxicité. Chez le chien, la
    dose sans effets observables a été fixée à 300 mg/kg de nourriture.

         Chez des souris mâles et femelles qui avaient reçu une
    nourriture contenant 5000 mg de carbendazime/kg de nourriture on a
    observé une augmentation du poids absolu du foie. Chez des souris
    mâles ayant reçu 1500 mg de carbendazime/kg de nourriture on a
    également observé une importante hypertrophie centrilobulaire avec
    nécrose et hypertrophie générale du foie.

    1.6.5  Reproduction, embryotoxicité et tératogénicité

         Lors d'une étude de reproduction portant sur trois générations,
    on a administré à des rats du carbendazime à des doses allant
    jusqu'à 500 mg/kg de nourriture inclusivement; aucun effet nocif n'a
    été constaté sur la reproduction de ces animaux. En revanche, après
    administration du même produit par gavage pendant 85 jour à raison
    de 200 mg/kg/jour, on constatait une réduction de la fertilité des
    mâles. A la dose de 50 mg/kg de poids corporel, la même étude a
    révélé une réduction sensible du nombre de spermatozoïdes
    épididymaires.

         Après administration par voie orale d'une dose unique de
    carbendazime et examen histologique, on a constaté que dès les deux
    premiers jours, il y avait une forte perturbation de la
    spermatogénèse avec occlusion des canaux efférents et augmentation
    du poids des testicules à la dose de 100 mg/kg de poids corporel.
    Aucun effet n'a été observé au cours de la même étude à la dose de
    50 mg/kg. Ces effets ont persisté jusqu'au 70ème jour chez les rats
    ayant reçu 400 mg/kg.

         Administré à des rats en doses quotidiennes supérieures à 10
    mg/kg du 7ème au 16ème jour de la gestation, le carbendazime a
    provoqué une augmentation du nombre de malformations et d'anomalies
    chez le rat. On constatait également une légère diminution du taux
    de nidation chez des lapines qui en avaient reçu respectivement 20
    ou 125 mg/kg en doses quotidiennes du 7ème au 19ème jour de la
    gestation ainsi qu'un accroissement de la fréquence des résorptions
    à la dose quotidienne de 125 mg/kg. Le composé s'est révélé toxique
    pour la mère, chez la ratte, à la dose quotidienne de 20 mg/kg et
    chez la lapine à la dose quotidienne de 125 mg/kg.

         Outre que le taux de gravidité était en diminution et que la
    fréquence des résorptions précoces était en augmentation chez le
    rat, il y avait une réduction sensible du poids des foetus aux doses
    quotidiennes respectives de 20 et 90 mg/kg, et un accroissement
    également notable des malformations à la dose quotidienne de 90
    mg/kg. Il s'agissait essentiellement d'hydrocéphalie, de
    microphthalmie, d'anophthalmie, de malformations des omoplates et de
    la partie axiale du squelette (fusions vertébrales, costales et
    sternébrales, exencéphalie, hémivertèbres et hyperplasie costale).
    Toutefois on n'a pas constaté de malformations importantes chez le
    lapin.

    1.6.6  Mutagénicité et autres points d'aboutissement des effets
           toxiques

         Les épreuves effectuées  in vitro et  in vivo sur des
    systèmes mammaliens et non-mammaliens ainsi que sur des cellules
    somatiques ou germinales montrent que le carbendazime n'interagit
    pas avec l'ADN, qu'il ne provoque pas de mutations ponctuelles et ne
    cause pas de mutation des cellules germinales.

         Toutefois le carbendazime provoque des aberrations dans le
    nombre des chromosomes (aneuploïdie et/ou polyloïdie) dans les
    systèmes d'épreuve (tant  in vitro qu' in vivo).

    1.6.7  Cancérogénicité

         L'administration de bénomyl et de carbendazime mêlés à la
    nourriture a provoqué chez des souris CD-1 et Swiss axéniques une
    augmentation dans l'incidence des tumeurs hépatocellulaires.

         Une étude de cancérogénicité a été effectuée avec le
    carbendazime sur des souris CD-1; elle a révélé une augmentation
    statistiquement significative et liée à la dose dans l'incidence des
    néoplasmes hépatocellulaires chez les femelles. Il y avait également
    une augmentation statistiquement significative à la dose moyenne
    (1500 mg/kg) de ces anomalies chez les mâles, augmentation qui n'a
    pas été constatée aux doses élevées en raison du taux élevé de
    mortalité. Une autre étude de cancérogénicité portant sur le
    carbendazime a été effectuée chez une souche génétiquement
    apparentée de souris Swiss axéniques et exogames à des doses de 0,
    150, 300 et 1000 mg/kg (la dernière dose étant portée 5000 mg/kg au
    cours de l'étude); elle a révélé un accroissement dans l'incidence
    de l'ensemble de adénomes et carcinomes hépatocellulaires. Une
    troisième étude, effectuée cette fois sur des souris NMRKf à des
    doses respectives de 0, 50, 150, 300 et 1000 mg/kg de nourriture (la
    dernière dose étant également portée à 5000 mg/kg au cours de
    l'étude) n'a cette fois pas fait ressortir d'effets cancérogènes. Le
    bénomyl ou le carbendazime ont provoqué indifféremment des tumeurs
    hépatiques chez deux souches de souris (CD-1 et axéniques), souches
    qui présentent toutes deux un taux élevé de tumeurs hépatiques
    spontanées. En revanche, le carbendazime n'est pas cancérogène chez
    les souris NMRKf dont le taux de tumeurs spontanées du foie est
    faible.

         Les études de cancérogénicité portant sur le bénomyl et le
    carbendazime ont donné des résultats négatifs chez le rat.

    1.6.8  Mécanisme de la toxicité - mode d'action

         On pense que les effets biologiques du bénomyl et du
    carbendazime résultent de leur interaction avec les microtubules
    cellulaires. Ces structures interviennent dans des fonctions aussi

    importantes que la division cellulaire, qui est inhibée par ces deux
    substances. La toxicité du bénomyl et du carbendazime pour les
    mammifères est donc liée à une perturbation des fonctions du système
    microtubulaire.

         Comme les autres dérivés du benzimidazole, le bénomyl et le
    carbendazime sont plus ou moins toxiques selon les espèces. Cette
    sélectivité toxicologique s'explique au moins en partie par le fait
    que les deux substances ne se lient pas de la même manière aux
    tubulines des espèces visées et des espèces non-visées.

    1.7  Effets sur l'homme

         Aucun effet nocif pour la santé humaine n'a été signalé.

    1.8  Effets sur les autres êtres vivants, en laboratoire et dans leur
         milieu naturel

         Le carbendazime n'a guère d'effet sur l'activité microbienne du
    sol aux doses d'emploi recommandées. On a cependant signalé
    l'existence d'effets nocifs vis-à-vis de certains groupes de
    champignons.

         On a calculé que la CE50 à 72 heures, fondée sur la
    croissance totale, pour les algues bleu-vert du genre  Selenastrum
     capricornutum, était égale à 1,3 mg/litre; la concentration sans
    effets observables était de 0,5 mg/litre. La toxicité du
    carbendazime pour les invertébrés aquatiques et les poissons varie
    largement, les valeurs de la CL50 à 96 heures allant de 0,007
    mg/litre pour des poissons chats du genre  Ictalurus, à 5,5
    mg/litre pour  Lepomis machrochirus. Une étude de 21 jours sur la
    daphnie  Daphnia magna, a révélé que, à la dose de 0,025 mg/litre,
    le déclenchement de la reproduction était sensiblement retardé; la
    concentration sans effets observables a été fixée à 0,013 mg/litre
    dans ce cas.

         Le carbendazime se montre toxique pour les lombrics dans des
    expériences de laboratoire reproduisant les conditions réelles
    d'exposition qui résultent d'une utilisation dans les conditions
    recommandées sur le terrain. Il est "relativement non toxique" pour
    les abeilles et peu toxique pour les oiseaux.

    2.  Conclusions

         Le bénomyl, un composé voisin du carbendazime, provoque une
    sensibilisation cutanée chez l'homme. Ce composé et le carbendazime
    lui-même ne présentent guère de risques d'intoxication aiguë pour
    l'homme. Etant donné les conditions actuelles d'exposition et le
    faible taux d'absorption percutanée de ces deux composés, il est
    improbable qu'ils provoquent des effets toxiques généralisés dans la
    population ou chez les personnes exposées pour des raisons

    professionnelles. Ces conclusions résultent des données relatives à
    l'animal et dans une moindre mesure des données relatives à l'homme;
    elles reposent sur la connaissance du mode d'action du carbendazime
    et du bénomyl, tant chez les espèces visées que chez les autres.

         Grâce à une meilleure connaissance du mécanisme de la toxicité
    du bénomyl et du carbendazime chez les mammifères, on pourra
    peut-être mieux déterminer quelles sont les doses sans effets
    observables. Des études portant sur la liaison de ces composés aux
    tubulines des cellules cibles (tissus testiculaires et
    embryonnaires) faciliteront sans doute les comparaisons
    interspécifiques.

         Le carbendazime est fortement adsorbé aux matières organiques
    du sol et il y persiste pendant des périodes allant jusqu'à trois
    ans. Il persiste également sur le feuillage et se retrouve par
    conséquent dans les feuilles mortes. On a montré que les lombrics
    pouvaient souffrir (dans leur effectif comme dans leur reproduction)
    de l'action de ces composés aux doses d'emploi recommandées. On ne
    possède aucune données sur les autres arthropodes qui vivent dans le
    sol ou sur les débris organiques et qui pourraient être exposés de
    la même manière.

         Il est improbable que la forte toxicité que, selon les études
    de la laboratoire, le carbendazime présente pour les organismes
    aquatiques, s'observe également dans le milieu naturel, du fait de
    la faible biodisponibilité des résidus de ce composé liés aux
    sédiments. Toutefois on ne possède aucune donnée sur les espèce
    sédimenticoles, qui seraient les plus exposées.

    RESUMEN Y CONCLUSIONES

    1.  Resumen

    1.1  Identidad, propiedades físicas y químicas y métodos analíticos

         La carbendazima es una sustancia sólida cristalina de color
    blanco y acción fungicida sistémica que pertenece a la familia del
    bencimidazol. Su punto de fusión es de unos 250 °C y tiene una
    presión de vapor de < 1 x 10-7 Pa (< 1 x 10-9 mbar). Es
    prácticamente insoluble en agua (8 mg/litro) a pH 7 y 20 °C. Es un
    compuesto estable en condiciones de almacenamiento normales.

         Los análisis de las muestras de residuos y del medio ambiente
    se realizan mediante extracción con un disolvente orgánico y
    purificación del extracto obtenido utilizando un procedimiento de
    reparto líquido-líquido. La valoración de los residuos se puede
    realizar mediante cromatografía líquida de alto rendimiento o
    inmunoensayo.

    1.2  Fuentes de exposición humana y ambiental

         La carbendazima es la sustancia más ampliamente utilizada de la
    familia de los fungicidas bencimidazólicos. Está formulada como
    dispersión acuosa, suspensión acuosa, gránulos fluidos dispersables
    en agua y polvo humectable.

    1.3  Transporte, distribución y transformación en el medio ambiente

         En el medio ambiente, el benomilo se transforma rápidamente en
    carbendazima, con una semivida de 2 y 19 h en el agua y en el suelo,
    respectivamente. Por consiguiente, para la evaluación de los efectos
    sobre el medio ambiente son importantes los datos obtenidos de los
    estudios realizados con ambos compuestos.

         La carbendazima se descompone en el medio ambiente, con una
    semivida de 6 a 12 meses en el suelo desnudo, de 3 a 6 meses en el
    césped y de 2 y 25 meses en el agua en condiciones aerobias y
    anaerobias, respectivamente. La descomposición se debe sobre todo a
    la acción de los microorganismos; el principal producto de su
    degradación es el 2-aminobencimidazol (2-AB), que luego se
    descompone de nuevo, también por la actividad microbiana. En la
    descomposición del benomilo marcado con un grupo fenilo con 14C,
    sólo el 9% del 14C formó CO2 durante un año de incubación,
    mientras que el resto del 14C se recuperó sobre todo como
    carbendazima y en productos unidos a residuos. El destino de un
    posible producto de degradación (1,2-diaminobenceno) puede aclarar
    ulteriormente la vía de degradación de los fungicidas
    bencimidazólicos en el medio ambiente.

         En estudios de campo y de columna se ha puesto de manifiesto
    que la carbendazima queda retenida en la capa superficial del suelo.
    Aunque no se dispone de datos sobre su adsorción en el suelo, es
    probable que ésta sea tan intensa como la del benomilo (los valores
    de Koc oscilan entre 1000 y 3600). Los valores del log Kow para
    el benomilo y la carbendazima son respectivamente 1,36 y 1,49.

         En la evaluación realizada en un modelo de selección, basado en
    datos de adsorción y persistencia, se puso de manifiesto que no
    había riesgo de lixiviación. En los Estados Unidos se han efectuado
    análisis de agua de pozos que confirman esto, puesto que no se
    encontraron trazas de carbendazima en ninguno de los 212 pozos
    muestreados (no se dispone del límite de detección). Es de suponer
    que la escorrentía superficial del benomilo y la carbendazima se
    deba solamente al fungicida adsorbido en las partículas del suelo y
    que en el medio acuoso estén fuertemente adsorbidos en los
    sedimentos.

         La carbendazima se hidroliza a 2-AB. Este es también el
    metabolito primario en el suelo y las plantas.

         En los sistemas animales se metaboliza a
    (5-hidroxi-1H-bencimidazol-2-il)-carbamato (5-HBC) y otros
    metabolitos polares, que se excretan rápidamente. No se ha observado
    que la carbendazima se acumule en ningún sistema biológico.

    1.4  Niveles medioambientales y exposición humana

         No parece que se disponga de datos de vigilancia ambiental para
    la carbendazima. Sin embargo, los estudios realizados sobre su
    destino en el medio ambiente pueden resumirse como sigue.

         Puesto que el benomilo y la carbendazima se mantienen estables
    en las plantas durante varias semanas, pueden pasar a los organismos
    que se alimentan de las hojas caídas. El suelo y los sedimentos
    pueden conservar residuos de carbendazima hasta tres años. Sin
    embargo, la fuerte adsorción de este compuesto en las partículas del
    suelo y en los sedimentos reduce la exposición de los organismos
    terrestres y acuáticos.

         La principal fuente de exposición para la población humana
    general se debe a los residuos de benomilo y carbendazima en los
    cultivos alimentarios. En análisis de la exposición a través de los
    alimentos realizados en los Estados Unidos (benomilo y carbendazima
    combinados) y en los Países Bajos (con carbendazima) se obtuvo una
    ingesta media prevista de alrededor del 10 por ciento de la ingesta
    diaria admisible (IDA) recomendada, de 0,02 mg/kg de peso corporal
    para el benomilo y de 0,01 mg/kg de peso corporal para la
    carbendazima.

         La exposición profesional durante el proceso de fabricación es
    inferior al valor umbral límite. Se considera que los trabajadores
    agrícolas que se ocupan de mezclar y cargar los plaguicidas o que
    entran en campos tratados con benomilo sufren exposición cutánea a
    unos mg de benomilo por hora. Esta forma de exposición se podría
    reducir con algún tipo de protección. Por otra parte, puesto que la
    absorción cutánea que cabe prever es baja, la probabilidad de que el
    benomilo tenga efectos tóxicos sistémicos a través de esta vía es
    muy escasa.

    1.5  Cinética y metabolismo

         La carbendazima se absorbe bien tras la exposición oral
    (80-85%), pero mucho menos después de una exposición cutánea. Una
    vez absorbida, se metaboliza formando numerosos compuestos en el
    organismo. Los principales metabolitos son el 5-HBC y los óxidos de
    5,6-HOBC-N; otros menos son importantes el 5,6-DHBC-S y el
    5,6-DHBC-G.

         La distribución de la carbendazima en los tejidos demuestra la
    ausencia de bioconcentración. En la rata, la concentración más
    elevada tras su administración oral (< 1% de la dosis) se produjo
    en el hígado. Apareció carbendazima en las mitocondrias, el
    metabolito 5-HBC en el citosol y el 2-AB en los microsomas. Aunque
    se encontraron también carbendazima y sus metabolitos en el riñón de
    gallinas y de vacas, no se detectaron niveles significativos en
    otros tejidos. Tras suministrar carbendazima con el pienso a vacas
    lactantes, se encontraron pequeñas cantidades de 5-HBC y 4-HBC en la
    leche.

         La carbendazima se excreta en la orina y las heces en un plazo
    de 72 h tras la dosificación oral en ratas.

         En ratas y ratones, la administración de dosis altas de
    carbendazima en la dieta o con sonda afectó a ciertas enzimas de los
    microsomas. Se produjo inducción de la estireno-7,8-hidrolasa y de
    la epóxido-hidrolasa, mientras que se redujo la actividad de la
    hidroxicumarín-O-deetilasa. También se indujo la actividad de la
    glutatión-S-transferasa citosólica.

    1.6  Efectos en los mamíferos de laboratorio y en sistemas de prueba
         in vitro

    1.6.1  Exposición única

         La carbendazima tiene una toxicidad aguda baja. Los valores de
    la DL50 oscilan entre > 2000 y 15 000 mg/kg en una amplia
    variedad de animales de experimentación y de vías de administración.

    Sin embargo, se han observado efectos reproductivos adversos
    significativos en la salud tras una exposición única (véase la
    sección 1.6.5).

    1.6.2  Exposición de corta duración

         La administración de carbendazima en la dieta durante un
    período de hasta 90 días produjo efectos leves en el peso del hígado
    de las ratas hembras expuestas a 360 mg/kg de peso corporal al día.
    En un estudio de alimentación con sonda a ratas durante 90 días, el
    NOEL fue de 16 mg/kg por día, basado en la hepatotoxicidad. Los
    estudios de alimentación de corta duración en perros no se
    consideraron adecuados para establecer un NOEL. En un estudio
    cutáneo de 10 días en conejos no se detectó toxicidad sistémica con
    la única dosis ensayada (200 mg/kg).

    1.6.3  Irritación y sensibilización cutánea y ocular

         La aplicación a la piel de conejos y cobayos no produjo
    irritación o sensibilización cutánea. Tras la aplicación a los ojos
    de conejos se observó una irritación conjuntival moderada o ligera.

    1.6.4  Exposición prolongada

         En ratas macho y hembra a las que se administraron 2500 mg/kg
    de alimentos se registró una disminución del número de eritrocitos y
    de los valores de la hemoglobina y el hematocrito. No se observó
    ninguna toxicidad de tipo hepático. Las ratas macho a las que se
    administraron 2500 mg/kg de alimentos o más presentaron un aumento
    marginal de la atrofia testicular y la prostatitis. El NOEL en las
    ratas es de 500 mg/kg de alimentos. En perros que recibieron una
    dieta con 500 mg de carbendazima por kg de alimentos durante un año
    o más se observó aumento del colesterol sérico, elevación de la
    actividad de la fosfatasa alcalina y otras indicaciones de
    hepatotoxicidad. El NOEL en perros es de 300 mg/kg de alimentos.

    1.6.5  Reproducción, embriotoxicidad y teratogenicidad

         La carbendazima no tuvo ningún efecto adverso en la
    reproducción cuando se administró a ratas en un estudio de
    reproducción de tres generaciones a dosis de hasta 500 mg/kg de
    alimentos. Se registró una reducción de la fecundidad masculina en
    las ratas a las que se administró carbendazima (200 mg/kg por día)
    con sonda durante 85 días. Con una dosis de 50 mg/kg de peso
    corporal al día en este estudio disminuyó considerablemente el
    número de espermatozoides en el epidídimo.

         Tras la administración a ratas de una dosis oral única de 100
    mg/kg de peso corporal, el examen histológico puso de manifiesto una
    interrupción temprana (0-2 días) de la espermatogénesis, con
    oclusión de los conductos eferentes y un aumento del peso de los

    testículos. En este estudio de dosis única no se observó ningún
    efecto con 50 mg/kg. Los efectos se mantuvieron hasta transcurridos
    70 días en ratas tratadas con 400 mg/kg.

         La carbendazima provocó un aumento de las malformaciones y las
    anomalías en las ratas administrada a dosis diarias superiores a 10
    mg/kg en los días 7-16 de la gestación. En conejas se produjo un
    ligero descenso de la tasa de implantación en dosis de 20 y 125
    mg/kg por día administradas en los días 7-19 de la gestación, y un
    aumento de la incidencia de la reabsorción a 125 mg/kg por día. Se
    observó toxicidad materna con dosis de 20 y de 125 mg/kg por día en
    ratas y conejos, respectivamente.

         Además del descenso de la tasa de gestaciones y del aumento de
    las reabsorciones precoces en la rata, se produjo una reducción
    significativa del peso del feto con dosis de 20 y 90 mg/kg por día,
    y un incremento significativo de las malformaciones fetales con la
    dosis de 90 mg/kg por día. Estas consistieron fundamentalmente en
    hidrocefalia, microftalmia, anoftalmia, malformaciones escapulares y
    del esqueleto axial (fusiones vertebrales, costales y esternebrales,
    exencefalia, hemivértebras e hiperplasia costal). Sin embargo, en
    los conejos no aparecieron malformaciones significativas.

    1.6.6  Mutagenicidad y otros efectos finales afines

         Los ensayos realizados en sistemas de mamíferos y no mamíferos
     in vitro e  in vivo y en células somáticas, así como en células
    germinales, demuestran que la carbendazima no tiene interacción con
    el ADN celular, no induce mutaciones puntuales y tampoco produce
    mutaciones de las células germinales.

         Sin embargo, la carbendazima provoca aberraciones cromosómicas
    numéricas (aneuploidía o poliploidía) en sistemas experimentales  in
     vitro e  in vivo.

    1.6.7  Carcinogenicidad

         La administración de benomilo y carbendazima con los alimentos
    a ratones CD-1 y suizos SPF dio lugar a un aumento de la incidencia
    de tumores hepatocelulares.

         Un estudio de carcinogenicidad de la carbendazima con ratones
    CD-1 puso de manifiesto un aumento estadísticamente signifi cativo,
    relacionado con la dosis, de la neoplasia hepatocelular en las
    hembras. También se observó un aumento estadísticamente
    significativo en los machos tratados con una dosis de nivel medio
    (1500 mg/kg de alimentos), pero no en los que recibieron dosis
    altas, a causa de la elevada mortalidad. Un estudio sobre la
    carcinogenicidad de la carbendazima en una raza de ratones
    genéticamente relacionada con la anterior, los ratones SPF (raza
    aleatoria suiza), con dosis de 0, 150, 300 y 1000 mg/kg de alimentos

    (que se aumentó a 5000 mg/kg durante el estudio), mostró un aumento
    de la incidencia de adenomas y carcinomas hepatocelulares
    combinados. Un tercer estudio realizado en ratones NMRKf con dosis
    de 0, 50, 150, 300 y 1000 mg de carbendazima por kg de alimentos
    (que se aumentó a 5000 mg/kg durante el estudio) no puso de
    manifiesto efectos carcinogénicos. El benomilo y la carbendazima
    provocaron tumores hepáticos en dos razas de ratones (CD-1 y SPF),
    ambas con un elevado índice de tumores hepáticos espontáneos. En
    cambio, la carbendazima no es carcinogénica en ratones NMRKf, que
    tienen un índice bajo de este tipo de tumores espontáneos.

         Los estudios de carcinogenicidad del benomilo y la carbendazima
    en ratas fueron negativos.

    1.6.8  Mecanismo de toxicidad, modo de acción

         Los efectos biológicos del benomilo y la carbendazima se deben
    a su interacción con los microtúbulos celulares. Estas estructuras
    intervienen en funciones esenciales, como la división celular, que
    inhiben el benomilo y la carbendazima. La toxicidad de estos
    productos en los mamíferos está vinculada a una disfunción
    microtubular.

         El benomilo y la carbendazima, al igual que otros compuestos
    del bencimidazol, tienen una toxicidad selectiva para distintas
    especies, que se explica, por lo menos en parte, porque el benomilo
    y la carbendazima se unen de manera distinta a los microtúbulos de
    las especies específicas en las que actúan y en las que no.

    1.7  Efectos en el ser humano

         No se ha informado de efectos adversos para la salud humana.

    1.8  Efectos en otros organismos en el laboratorio y en el medio
         ambiente

         Con las dosis de aplicación recomendadas, la carbendazima tiene
    pocos efectos sobre la actividad microbiana del suelo. Se han
    notificado algunos efectos adversos sobre ciertos tipos de hongos.

         La CE50 a las 72 horas para el alga verde  Selenastrum
     capricornutum, basada en el crecimiento total, se calculó en 1,3
    mg/litro; la NOEC fue de 0,5 mg/litro. La toxicidad de la
    carbendazima para los invertebrados acuáticos y los peces varía
    ampliamente, con una CL50 a las 96 h que oscila entre 0,007
    mg/litro para  Ictalurus punctatus y 5,5 mg/litro para  Lepomis
     macrochirus. En una prueba de 21 días con  Daphnia magna, el
    comienzo de la reproducción se retrasó considerablemente con 0,025
    mg/litro; la NOEC fue de 0,013 mg/litro.

         La carbendazima es tóxica para las lombrices de tierra en
    experimentos de laboratorio con una exposición a concentraciones
    normales y con las dosis de aplicación recomendadas en el campo. Es
    "relativamente no tóxica" para las abejas de miel y su toxicidad es
    baja para las aves.

    2.  Conclusiones

         El benomilo causa sensibilización cutánea en el ser humano.
    Tanto el benomilo como la carbendazima representan un riesgo muy
    pequeño de intoxicación aguda. Dados los niveles de exposición
    actuales y el bajo índice de absorción cutánea de estos dos
    compuestos, no es probable que puedan tener efectos de toxicidad
    sistémica en la población general o en personas expuestas
    profesionalmente. Estas son las conclusiones que se pueden sacar de
    los datos obtenidos en animales y de los limitados datos sobre el
    ser humano de que se dispone, pero estas extrapolaciones están
    respaldadas por el conocimiento del modo de acción de la
    carbendazima y el benomilo en especies en las que actúan y en las
    que no.

         Una mayor clarificación del mecanismo de toxicidad de ambos
    compuestos en los mamíferos permitirá quizás definir mejor los
    niveles sin efectos observados. El estudio de su unión a los
    microtúbulos de las células destinatarias (tejidos testicular y
    embrionario) facilitará la comparación entre distintas especies.

         La carbendazima se adsorbe fuertemente en la materia orgánica
    del suelo, que la conserva durante un período de hasta tres años.
    Persiste en la superficie de las hojas y, por consiguiente, en las
    hojas caídas. Se ha demostrado que las dosis recomendadas de
    aplicación afectan negativamente a las lombrices de tierra (con
    efectos sobre la población y la reproducción). No se dispone de
    datos acerca de sus efectos sobre otros artrópodos del suelo o de la
    maleza, que estarían igualmente expuestos.

         No es probable que se pueda observar en el medio ambiente la
    elevada toxicidad demostrada en las pruebas de laboratorio para los
    organismos acuáticos, debido a la baja biodisponibilidad de los
    residuos de carbendazima unidos a los sedimentos. Sin embargo, no se
    dispone de información acerca de sus efectos en las especies que
    viven en los sedimentos, que sufrirían la exposición más intensa.


    See Also:
       Toxicological Abbreviations
       Carbendazim (HSG 82, 1993)
       Carbendazim (ICSC)
       Carbendazim (PDS)
       Carbendazim (WHO Pesticide Residues Series 3)
       Carbendazim (Pesticide residues in food: 1976 evaluations)
       Carbendazim (Pesticide residues in food: 1977 evaluations)
       Carbendazim (Pesticide residues in food: 1978 evaluations)
       Carbendazim (Pesticide residues in food: 1983 evaluations)
       Carbendazim (Pesticide residues in food: 1985 evaluations Part II Toxicology)
       Carbendazim (Pesticide residues in food: 1995 evaluations Part II Toxicological & Environmental)
       Carbendazim (Pesticide residues in food: 1995 evaluations Part II Toxicological & Environmental)
       Carbendazim (JMPR Evaluations 2005 Part II Toxicological)