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    FENAMIPHOS

    EXPLANATION

         A full toxicological evaluation of the available data was
    performed by the 1974 Joint Meeting (Annex 1, FAO/WHO, 1975a) and an
    acceptable daily intake of 0-0,0006 mg/kg b.w. was recommended. A
    toxicological monograph was prepared (Annex 1, FAO/WHO, 1975b). Since
    then a direct request for reevaluation has been received from a Member
    State. Additional data have been received and are reviewed in this
    monograph addendum.

    EVALUATION FOR ACCEPTABLE DAILY INTAKE

    BIOLOGICAL DATA

    Biochemical Aspects

    Effects on enzymes and other biochemical parameters

         Blood samples were extracted from an equal number of male and
    female Sprague-Dawley rats and then pooled to compare the in vitro
    cholinesterase depression by fenamiphos and five of its metabolites on
    plasma and erythrocyte cholinesterases. Substances tested included
    fenamiphos, fenamiphos sulfoxide, des-isopropyl fenamiphos sulfoxide,
    fenamiphos sulfone, des-isopropyl fenamiphos sulfone, and des-
    isopropyl fenamiphos. Samples were incubated for one hour, after which
    the cholinesterase (ChE) activity was determined. In vitro
    inhibition of plasma and red blood cell (RBC) cholinesterase are shown
    below in Tables 1 and 2. Erythrocyte cholinesterase was less sensitive
    to fenamiphos and its metabolites than was plasma cholinesterase (Lamb
    & Landes, 1978).

         Male and female TNO/W74 albino rats were exposed to aerosolized
    concentrations of fenamiphos (89.8% purity) four hours per day for
    five consecutive days.  Concentrations obtained were 0, 0.3, 0.6, 3.3,
    4, 9 and 28 mg/m3. Plasma and erythrocyte cholinesterase measurements
    were performed pre-exposure, after the 1st, 3rd and 5th exposure, and
    72 hours after the 5th exposure. Cholinesterases were depressed in a
    dose-related manner, with plasma ChE most significantly depressed and
    females the more sensitive sex. Plasma ChE was depressed 32 to 90% in
    males at > 3.3 mg/m3 and 31 to 96% in females at > 0.3 mg/m3.
    Plasma ChE remained 32 to 46% depressed for 72 hours after the fifth
    exposure in females at concentrations of > 9 mg/m3. There was no
    effect on erythrocyte ChE in males. However, erythrocyte ChE in
    females was depressed 28 to 46% at > 9 mg/m3 (Mihail, 1980).

    Table 1.  Plasma cholinestrase depression (%) induced
              in vitro by fenamiphos and its metabolites
                                                                  

                                  Dose (ppm) in whole blood
                        6.88      68.8      688       5440    6880
                                                                  

    Fenamiphos          -         0         10        49        69

    F. sulfoxide        18        41        48        -         85

    F. sulfone          0         13        50        -         87

    Des-isopropyl       6         40        90        -         93
     F. sulfoxide

    Des-isopropyl       0         20        69        -         90
     F. sulfone

    Des-isopropyl       -         2         13        71        91
     fenamiphos
                                                                  

    Table 2.  Erythrocyte colinesterase depression (%) induced
              in vitro by fenamiphos and its metabolites
                                                                   

                                  Dose (ppm) in whole blood
                        6.88      68.8      688       5440    6880
                                                                   

    Fenamiphos          -         0         0         0         23

    F. sulfoxide        5         0         5         -         52

    F. sulfone          8         -         -         -         -

    Des-isopropyl       4         0         47        -         50
     F. sulfoxide

    Des-isopropyl       6         0         32        -         61
     F. sulfone

    Des-isopropyl       -         8         0         32        53
     fenamiphos
                                                                   

    Toxicological studies

    Special studies on teratology

    Rabbit

         Groups of New Zealand rabbits (20 double-mated females per group)
    were administered fenamiphos (88.8% purity) orally in corn oil at
    doses of 0, 0.1, 0.3, or 1.0 mg/kg body weight from days 6 to 18 of
    gestation. Animals were observed daily for clinical signs of toxicity;
    they were weighed initially, periodically during the test and at
    terminiation. Pups were delivered by Caesarian section and the dams'
    ovaries and uteri examined. Foetuses were examined grossly and
    prepared for soft tissue and skeletal evaluations. The number of
    corpora lutea, implantations, resorptions, live and dead fetuses, and
    anomalies were determined.

         Dams administered > 0.3 mg/kg demonstrated decreased body-
    weight gain, bloody nasal discharge and white mucoid ocular discharge.
    There were no compound-related effects on the number of litters,
    number of pups per litter, pregnancy rate, the number of corpora
    lutea, implantations or gross abnormalities reported. Mean fetal
    weight was slightly depressed at 1.0 mg/kg. One dam at 0.3 mg/kg and
    2 dams at 1.0 mg/kg aborted 1 and 8 dead pups, and 7 late resorptions,
    respectively. In addition, 1 dead fetus was observed in each of 2
    litters at the high dose during Caesarian section.

         The most common developmental variation observed was the left
    carotid arising from the innominate which occurred in 6 to 8 fetuses
    (7 to 9%) in each of 3 litters (25%) at doses of > 0.1 mg/kg. There
    was no occurrence in the control group and only 1 of 31 litters (3.2%)
    noted in the historical control data from the lab performing the
    study. More recent historical control data (through July 1985) reveal
    the following:

                             Fetuses    %          Litters  %

    Left carotid             11/336    3.3       9/53      17
     arising from
     innominate

         There is some evidence that the incidence of left carotid
    anomalies increases in superovulated or artificially-inseminated
    rabbits. Interestingly, the rabbits used in this study were naturally
    bred, but the "newer" historical data are from artificially-
    inseminated rabbits. Furthermore, historical control data for the same
    strain of rabbit, but in different labs (also artificially
    inseminated) demonstrate that the left carotid arising from the
    innominate is also a frequent finding in that colony with roughly 8%
    of the fetuses and 25% of the litters demonstrating this anomaly.

    Therefore, the biological significance of this finding in relation to
    compound administration is dubious. There were, however, 2 fetuses in
    1 litter at the high dose with aortic arches having a common truncus,
    a finding considered to represent a major malformation.

         The incidence of accessory skull bones was observed in each of
    the 3 dose groups (> 0.1 mg/kg) but it did not occur in a dose
    related manner. A significant increase in the incidence of chain fused
    sternebrae was noted at 1.0 mg/kg, with a finding of 5 fetuses in 3
    litters. There was also 1 fetus in 1 litter at 0.3 mg/kg with a
    finding of chain fused sternebrae. Other skeletal malformations which
    occurred only at > to 0.3 mg/kg included fused ribs, scoliosis,
    absent vertebrae (thoracic, lumbar, sacral and caudal), and centra
    bipartite/malformed. Although these findings occurred in isolated
    incidences of 1 fetus in 1 litter they were not reported in control or
    0.1 mg/kg dose groups and, therefore, were considered related to
    treatment. Fenamiphos was not maternally toxic or teratogenic at
    0.1 mg/kg, but was considered fetotoxic at all levels tested
    (MacKenzie, 1982).

    Rat

         Data submitted were incomplete and illegible, rendering adequate
    interpretation and evaluation impossible. Individual animal data, by
    dam or by litter, were not provided, and visceral, skeletal, and gross
    abnormalities or anomalies were not tabulated (Schluter, 1981).

    Special Study on Carcinogenicity

    Mice

         Groups of 6-week-old CD, outbred strain albino mice (50 per sex
    per group) were administered fenamiphos (89.5% purity) in the diet at
    dose levels of 0, 2, 10 or 50 ppm for 20 months. Observations for
    toxicological effects were conducted daily. Body weights and food
    consumption were determined weekly. Haematogical parameters were
    analyzed at 6, 12, 18 and 20 months of the study. All animals
    underwent complete necropsy, including organ weights of liver, kidney,
    heart, lungs, gonads, spleen, brain and adrenals. A full complement of
    tissues and organs from all animals were examined histopathologically.

         Daily observations were not reported. Survival was comparable in
    all groups with only a marginal decrease at the high dose. Survival at
    20 months was 32 to 45%. The mean amount of fenamiphos consumed
    throughout the study was 0.3 mg/kg b.w. at 2 ppm, 1.4 to 1.8 mg/kg at
    10 ppm, and 7.4 to 8.8 mg/kg at 50 ppm. Food consumption and
    hematology were unaffected by treatment. Organ weights were variable
    with a dose-related decrease, although not significant, in relative
    brain weight in both sexes. Relative spleen weights were decreased in
    both sexes, but most notably in males at > 10 ppm, Relative weight
    of gonads in males was decreased at 50 ppm. Gross and micropathology

    evaluation did not identify the reason for these weight changes. The
    most frequent pathological finding reported was myocarditis (acute and
    chronic) in both sexes in all dose groups but without significant
    difference associated with dose. There was also a significant degree
    of fatty diffuse change in the liver, again without dose differences.
    Amyloidosis was observed in all groups and was uniformly widespread in
    many organ systems, including liver, spleen, adrenals and submaxillary
    salivary glands. Fenamiphos did not demostrate any oncogenic potential
    at doses up to and including 50 ppm (Hayes, 1982).

    Special Studies on Mutagenicity

         Several mutagenicity tests with different systems have been
    carried out on fenomiphos (Table 3). No evidence of a mutagenic
    potential was observed.

    Acute Toxicity

         Several acute toxicity studies have been carried out
    administering orally to rats fenamiphos or its metabolites. A few
    inhalation studies on fenamiphos are also available. The results are
    summarized in Table 4.

         Moreover, fenamiphos (91.8% purity) was administered orally to
    male Wistar rats together with Curaterr(R) VM75 (2,3-dihydro-2,2-
    dimethyl-7-benzofuranyl-N-methylcarbamate) to determine if the
    combination produced more than additive acute toxic effects. The acute
    oral LD50 (in rats) for fenamiphos and for Curaterr(R) VM75 was 4.6
    and 8.1 mg/kg, respectively. The mixture, which was essentially a 2:1
    ratio (Curaterr(R):fenamiphos), resulted in an LD50 of 6 mg/kg and
    demonstrated the combination was additive, but not synergistic
    (Mihail, 1980).

    Short-Term Studies

    Dog

         Groups of 4-month-old Beagle dogs (4M/4F per group) were
    administered fenamiphos (89% purity) in the diet at dose levels of 0,
    0.6, 1.0 or 1.7 ppm for 100 days. Animals were observed twice daily,
    and weekly body weight and food consumption measurements were
    recorded. Plasma and erythrocyte cholinesterase values were determined
    at 0, 4, 6, 8, 10 and 12 weeks. Brain cholinesterase was determined at
    termination of the study. Haematology, clinical chemistry, and
    urinalysis were not performed. The tissues/organs were not subjected
    to gross or histopathological examination.

        Table 3.  Results of mutagenicity assays on fenamiphos
                                                                                                                        

    Test System                   Test Object         Concentrations      Purity    Results             Reference
                                                      of fenamiphos
                                                      used
                                                                                                                        

    In vitro sister               Chinese             Activated:          ?         Negative            Chen &
     chromatid                    hamster cell        10, 20, 40,                   (1)                 Huang, 1982
     exchange assay               line V79            & 80 g/ml
     (with metabolic
     activation)

    CHO/HGPRT                     Chinese             Nonactivated:       85%       Negative            Yang et
     mutation assay               hamster ovary       100, 110, 120,                (2)                 al., 1984
     (3)                          cells               & 130 g/ml
                                  (CHO-K1-BH4)
                                                      Activated:
                                                      170, 190, 210,
                                                      & 230 g/ml

    Ames test (3)                 S. typhimurium,     20, 100, 125,       92.4%     Negative            Schulz,
                                  TA98, TA100,        250, 500,                                         1985
                                  TA1535              1,000, 2,000
                                  & TA1537            2,500 &
                                                      12,500 g/plate
                                                      dissolved in
                                                      DMSO

    Ames test (3)                 S. typhimurium,     4, 20, 100,         ?         Negative,           Herbold,
                                  TA98, TA100,        500, & 2,500                  but test            1979
                                  TA1535              g/plate                      procedure
                                  & TA1537            dissolved in                  considered
                                                      DMSO                          unacceptable
                                                                                                                        

    Table 3.  (Con't)
                                                                                                                        

    Test System                   Test Object         Concentrations      Purity    Results             Reference
                                                      of fenamiphos
                                                      used
                                                                                                                        

    Micronucleus                  Mice (NMRI          0.625, 1.25,        92.5%     Negative,           Herbold,
     test                         strain)             & 2.5 mg/kg                   but test            1980a
                                                      (administered                 procedure
                                                      orally twice,                 considered
                                                      24 hr apart)                  unacceptable

    Dominant lethal               Mice (male)         5 mg/kg             92.5%     Negative            Herbold,
                                  (NMRI strain)       (mortality at                                     1980b
                                                      10 mg/kg - 3/5
                                                      & at 15 mg/kg
                                                      - 5/5)
                                                                                                                        

    (1)  Positive control (Cyclophosphamide) gave expected positive response at 5 g/ml.
    (2)  Positive controls (EMS 0.2 l/ml; BaP 2 g/ml) yielded expected positive response.
    (3)  Both with and without metabolic activation.
            Table 4.  Results of acute toxicity assays in rats of fenamiphos and its metabolites
                                                                                                           

    Substance                                         LD50           LC50
    Tested                   Sex       Route          (mg/kg b.w.)   (mg/m3)        Reference
                                                                                                           

    Fenamiphos               M         oral           2.7                           Lamb & Matzkanin,
     (88% purity)            F         oral           3.0                           1975

    Fenamiphos (90.2%        M         oral(l)        5.75                          Heiman, 1981
     purity)                           oral(2)        17.2

    Fenamiphos               M         oral(l)        5.8                           Heiman, 1984
                                       oral(2)        21.0

    Fenamiphos               M         oral(l)        2.4                           Crawford &
     (88% purity)            F         oral(l)        3.3                           Anderson, 1974a

    Fenamiphos               M         oral(l)        3.15                          Crawford &
     (analytical grade       F         oral(l)        2.38                          Anderson, 1973
     99.7% purity)

    Fenamiphos               M         oral           2.6                           Crawford &
     sulfone                 F         oral           2.4                           Anderson, 1974b

    Fenamiphos               M         oral           2.4                           Crawford &
     sulfoxide               F         oral           2.4                           Anderson, 1974b

    Des-isopropyl            M         oral           1.4                           Lamb & Matzkanin,
     fenamiphos              F         oral           2.1                           1977

    Des-isopropyl            M         oral           4.1                           Lamb & Matzkanin,
     fenamiphos              F         oral           3.7                           1975
     sulfoxide
     (95% purity)
                                                                                                           

    Table 4.  (Con't)
                                                                                                           

    Substance                                         LD50           LC50
    Tested                   Sex       Route          (mg/kg b.w.)   (mg/m3)        Reference
                                                                                                           
    Fenamiphos (89.8%        M         inhal.                        131(3)         Thyssen, 1979a
     purity)                 F         inhal.                        130(3)

    Fenamiphos (89.8%        M         inhal.                        100(4)         Thyssen, 1979a
     purity)                 F         inhal.                        100(4)
                                                                                                           

    (1)  Fasted animals           (3) 1 hr exposure
    (2)  Non-fasted animals       (4) 4 hr exposure
    
         There were no toxicological symptoms or effects on body weight
    and food consumption. Erythrocyte and brain cholinesterase were
    unaffected by treatment. However, plasma cholinesterase was depressed
    28 to 35% in males given 1.7 ppm (equal to 0.358 mg/kg b.w.) in the
    diet. Females were not similarly sensitive (Hayes, 1983).

    Rabbit - Dermal

         An aqueous formulation of technical fenamiphos (89.8% purity) was
    applied to the clipped dorsal area of 6 male and 6 female New Zealand
    rabbits at 0, 2.5 and 10 mg/kg b.w. for 6 hours/day, 5 days/week for 3
    weeks. Two additional groups, dosed at 0 and 0.5 mg/kg b.w. were
    treated similar to preceding groups. Half of the animals of each group
    were abraded.

         No signs of toxicity or mortality were observed. Body-weight
    gains were decreased in both sexes at the 10 mg/kg dose level. Slight
    erythema was observed in all groups during the initial week for
    abraded skin sites only, which cleared by day 7. There were no
    apparent differences between test and control groups for hematology,
    urinalysis, and clinical chemistry determinations. Gross necropsy,
    histopathology, and organ weight measurements were unremarkable in
    comparison to control. Plasma and erythrocyte cholinesterase values
    were significantly depressed at 10 mg/kg in both male and female
    rabbits. However, females were somewhat more sensitive and
    demonstrated depressed plasma ChE levels at 2.5 mg/kg as well. Brain
    ChE values for females at 2.5 mg/kg and 10 mg/kg were depressed by 19
    and 23%, respectively. A dose of 0.5 mg/kg, applied dermally, was
    without demonstrated effect on cholinesterase activity (Mihail &
    Schilde, 1980).

         In a separate study, soil containing up to 200 ppm fenamiphos and
    fenamiphos sulfoxide, applied to the shaved skin of New Zealand
    rabbits, via either single 24 hr. or 5 consecutive 6 hr. exposures did
    not adversely affect plasma or erythrocyte cholinesterase activity
    (Hixson, 1981).

    Rat - Dermal

         Male rats were dosed dermally with 100 to 400 g/cm fenamiphos,
    25 to 800 g/cm fenamiphos sulfoxide or 200 to 1600 g/cm fenamiphos
    sulfone. Test material in acetone was applied and allowed to dry on
    the clipped dorsal area of male rats. After 72 hours the animals were
    sacrificed and erythrocyte ChE activity determined. Fifty percent
    inhibition of erythrocyte ChE activity was achieved with a dose of
    208 g/cm for fenamiphos, 262 g/cm for fenamiphos sulfoxide and
    750 g/cm for fenamiphos sulfone (Knaak, 1981).

    Rat - Inhalation

         Three groups of 10 male and 10 female Wistar TNO/W albino rats
    weighing 180 to 220 grams were exposed to technical fenamiphos (92.2%
    purity) at 0.0, 0.03, 0.25 or 3.5 g active ingredient/litre
    6 hrs./day, 5 days/week, for 3 weeks. Technical fenamiphos was diluted
    with a 1:1 mixture of ethanol and polyethylene glycol 400 for
    aerosolization in a dynamic flow inhalation chamber.

         There were no toxic signs or effects on mortality, body weight
    gain, hematology, urinalysis or clinical chemistry measurements. A
    significant decrease in plasma and a slight decrease in erythrocyte
    ChE for both sexes was noted at 3.5 g/litre. Brain ChE activity was
    not affected. Ninety-eight percent of the particles were 3 microns or
    less. There were no gross or histopathological changes, or effects on
    organ weights. (Thyssen, 1979b).

    Cattle

         Dairy cows (1 control, 3 per test group) were fed fenamiphos
    sulfoxide in their diets at 0, 2, 6 or 20 ppm for 29 days. There were
    no apparent effects of dosing observed based on behaviour, feed
    consumption, milk production and body-weight gain. Determination of
    whole blood cholinesterase revealed no adverse effects at 2 and 6 ppm.
    However, at 20 ppm, significant depression (51%) was observed (Wargo,
    1978).

    COMMENTS

         Data submitted and evaluated by the 1985 Joint Meeting support
    the conclusions of the 1974 Meeting with regard to acute toxicity and
    anti-cholinesterase potency. Various purities of technical fenamiphos
    (88 to 99.7%) produced the same degree of acute oral toxicity to rats.
    The major plant and animal metabolites were equally toxic (e.g. 2 to
    3 mg/kg/b.w.).

         Fenamiphos and its cholinesterase inhibiting metabolites are
    better inhibitors of plasma than erythrocyte cholinesterase.

         In a 100-day dog feeding study, fenamiphos inhibited only plasma
    cholinesterase in males at 1.7 ppm, but not at 1.0 ppm.

         Fenamiphos was not maternally toxic or teratogenic in rabbits at
    a dose of 0.1 mg/kg b.w. However, fenamiphos was considered fetotoxic
    at all doses administered and was found to cause an increased
    incidence of chain fused sternebrae at and above 0.3 mg/kg b.w.

         Fenamiphos was not oncogenic in a mouse carcinogenicity study,
    nor was it mutagenic in several mutagenicity assays.

         The rabbit teratology and mouse oncogenicity studies reviewed in
    this monograph addendum are acceptable replacement studies for the
    corresponding IBT studies reviewed in 1974 and which were subsequently
    determined to be invalid.

         Very limited new data were available which were evaluated and
    have been included in the monograph addendum. The Meeting determined
    that additional studies, including rat oncogenicity, rat reproduction,
    rat teratology and rabbit teratology with NOEL for fetotoxicity, are
    necessary for estimation of a full ADI.

         A full reevaluation was not performed, but the meeting
    recommended that such an evaluation be performed when the ongoing rat
    oncogenicity study becomes available in 1986. The ADI was converted to
    a temporary ADI with an increased safety factor to reflect the concern
    of the Meeting for fetotoxicity demonstrated in the rabbit teratology
    study.

    TOXICOLOGICAL EVALUATION

    LEVEL CAUSING NO TOXICOLOGICAL EFFECT

         Rat: 3 ppm in the diet, equivalent to 0.17 mg/kg b.w.

         Dog: 1 ppm in the diet, equivalent to 0.025 mg/kg b.w.

    ESTIMATE OF TEMPORARY ACCEPTABLE DAILY INTAKE FOR MAN

         0 - 0.0003 mg/kg b.w

    FURTHER WORK OR INFORMATION REQUIRED (by 1986)

    1.   Submission of the results of ongoing rat oncogenicity study.

    2.   Submission of a full legible report and raw data for the rat
         teratology study.

    3.   New rabbit teratology study to clarify the fetoxicity observed at
         low dietary levels.

    Desirable

         Observations in man.

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    (1978)    cattle. Chem. Agr. Div., Mobay Chemical Corporation Rep. No.
              66,212. Unpublished data submitted by Bayer to WHO.

    Yang, L.L., Putman, D.L., & Conklin, P.M. CHO/HGPRT mutation assay in
    (1984)    the presence and absence of exogenous metabolic activation -
              Nemacur(R). Study No. T2600.332. Unpublished report
              submitted by Bayer to WHO.
    


    See Also:
       Toxicological Abbreviations
       Fenamiphos (ICSC)
       Fenamiphos (WHO Pesticide Residues Series 4)
       Fenamiphos (Pesticide residues in food: 1977 evaluations)
       Fenamiphos (Pesticide residues in food: 1978 evaluations)
       Fenamiphos (Pesticide residues in food: 1980 evaluations)
       Fenamiphos (Pesticide residues in food: 1987 evaluations Part II Toxicology)
       Fenamiphos (Pesticide residues in food: 1997 evaluations Part II Toxicological & Environmental)
       Fenamiphos (JMPR Evaluations 2002 Part II Toxicological)