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
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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
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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:
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.
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 fertilit