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    PERMETHRIN

    EXPLANATION

         Permethrin, a mixture of 4 stereoisomers has been reviewed for
    acceptable intake by previous JMPR's in 1979, 1981 and 1982 Annex 1,
    FAO/WHO 1980a, 1982a and 1983a). The 1982 JMPR established an ADI for
    the 40:60 cis:trans mixture of permethrin stereoisomers only since it
    recognized that other mixtures of permethrin stereoisomers in
    different isomeric ratios would require independent evaluation. The
    present evaluation related to permethrin mixture in which the
    cis:trans ratio is nominally 25:75.

    EVALUATION FOR ACCEPTABLE INTAKE

    BIOLOGICAL DATA

    Toxicological studies

    Special Study on Carcinogenicity

    Mice

         Groups of 75 male and 75 female Anglia CFLP mice received
    permethrin (25:75) in their diet at 10, 50 and 250 mg/kg/day for
    91 weeks. Control groups consisted of 100 animals of each sex. No
    significant differences in mortality were apparent between the treated
    and control animals. Body weight gains of treated animals were
    comparable to controls. The food intake of the high dose female group
    was decreased in the final ten weeks of treatment only.

         At necropsy, there were slight but significant increases in liver
    weight of high-dose males and in renal weight of high-dose females.
    Lymphoid hyperplasia, malignant lymphoma and reticulum cell sarcoma
    were frequent in all groups but their incidences were unrelated to
    treatment. The incidence of pulmonary adenoma was increased in high
    dose females and reduced in high dose males in comparison to controls.
    However, these incidences remained within historical control ranges
    for this strain. Hemangiomas and hemangiosarcomas occurred in the
    liver and at other sites in each sex, but were not related to
    treatment. The results of this study do not indicate any carcinogenic
    potential for permethrin (James et al., 1980).

    Special Study on Dermal Sensitisation

    Guinea Pigs

         Permethrin (25:75) in corn oil (1% w/v) or Freund's complete
    adjuvant (1% w/v) did not induce dermal sensitisation in groups of
    10 male guinea pigs when applied as a 25% dispersion in petrolatum.
    The positive control, 2,4-dinitrochlorobenzene, (5% w/v) in petrolatum
    produced marked sensitisation. Thus, permethrin (25:75) did not
    produce either dermal irritancy or sensitisation under test.
    conditions (Chesher & Malone, 1974b).

    Special Study on Teratogenicity

         Groups of 22-23 female Wistar rats received permethrin (25:75) at
    0 or 200 mg/kg in corn oil by daily oral savage on days 6-16 of
    pregnancy inclusive. Treatment was without apparent effect on maternal
    bodyweight gain or general condition. The animals were sacrificed on
    day 20 so that their uterine contents could be examined. Treatment had

    no effect on the number of corpora lutea, implantations, live fetuses,
    early and late fetal deaths and fetal abnormalities. Examination of
    the fetuses, including dissection and skeletal staining, showed no
    morphological effects of treatment. These results indicate that
    permethrin (25:75) is not fetotoxic in rats at 200 mg/kg/day
    (James, 1974).

    Special Study on Neurotoxicity

    Rats

         Groups of 10 male and 10 female Sprague Dawley rats received
    permethrin (25:75) (94.5% pure) in the diet at 0, 4000, 6000 and
    9000 ppm for 21 days. All treated animals developed severe trembling
    and lost weight. Some of the high-dose rats of each sex died.

         Subsequent histopathological examination of brain, spinal cord,
    trigeminal and dorsal root ganglia, proximal and distal root trunks as
    well as terminal motor and sensory nerves revealed no consistent
    histopathological abnormality (Dayan, 1980).

    Special Study on Ocular Irritancy

    Rabbits

         Permethrin (25:75) (40% in corn oil) did not produce any ocular
    effects when instilled (0.1 ml) into the ocular sac of New Zealand
    rabbits (Chesher & Malone, 1974c).

    Special Studies on Mutagenicity

         Mutagenicity study results are presented in Table 1.

    Special Studies on Reproduction

    Rats

         In a 3-generation reproduction study, groups of 20 male and
    20 female Wistar COBS rats received permethrin in the diet at 0, 5, 30
    and 180 mg/kg/day during growth, mating, gestation, parturition and
    lactation for 3 generations, each with 2 litters.

         Fetal toxicity and teratogenicity was assessed in the second
    pregnancy of the F2 generation


        Table 1:  Special Studies on Mutagenicity
                                                                                                                          

    Test System            Test Organism           Concentration               Result            Reference
                                                                                                                          

    Ames Test              S. typhimurium          Permethrin (25:75)          Negative          Simmon, 1976
     metabolic            TA 1535, TA 1537,       1, 50, 100, 250,
    activation             TA 1538, TA 98,         500, 1000 (ug/plate)
                           TA 100                  N-methyl-N-nitro-
                                                   N-nitrosoguanidine          Positive
                                                   4-O-tolylazo-O-             Positive with
                                                   toluidine (ug/plate)        metabolic
                                                                               activation
                           E. coli WP2             Permethrin (25:75)          Negative          Simmon, 1976
                                                   1, 50, 100, 250,
                                                   500, 1000 ug/plate

    Ames Test              S. typhimurium          Permethrin (25:75)          Negative          Clive, 1979
                           TA 1535, TA 1537,       1.3, 2.5, 5, 10, 20,
                           TA 1538, TA 98,         30, 40, 50 ug/plate
                           TA 100

    Mouse Lymphoma         L5178Y                  Permethrin (25:75)          Negative          Clive, 1977
    Assay                 Mouse Lymphoma Cells    0, 31, 47, 62, 94, 125
    Metabolic activation                           (ug/ml) 0, 20, 30, 40,
                                                   50 (with activation)
                                                   ethylmethane sulphonate     Positive
                                                   (620 ug/ml)
                                                                                                                          

    Table 1:  Special Studies on Mutagenicity (cont'd)
                                                                                                                          

    Test System            Test Organism           Concentration               Result            Reference
                                                                                                                          

                                                   2-acetylaminofluorene       Positive
                                                   (with activation)
                                                   (50 ug/ml)
                                                   dimethyl nitrosamine        Positive
                                                   (75 ug/ml)

    Dominant Lethal        CD-1 mice               Permethrin (25:75)          Negative          Chesher et al., 1975b
    Assay                                          (452 mg/kg)
                                                   trimethyl phosphate         Positive
                                                                                                                          
    
         Treatment with permethrin had no effect on general behaviour, and
    condition, food intake, bodyweight gain, pregnancy rate of the dams.
    No effects were seen on parturition, sex ratio or pup weight. A small
    number of rats of each group developed eye abnormalities, including
    ocular hemorrage and chronic glaucoma but there was no relationship to
    treatment. Examination of F3b fetuses showed no treatment-related
    effect on sex ratio, bodyweight or the occurrence of visceral or
    skeletal abnormalities. The results of this study indicate that
    permethrin (25:75) has no effect on the reproduction of rats at doses
    up to 180 mg/kg/day (James, 1979).

    Acute Toxicity

         The acute toxicity of permethrin (25:75) to groups of 6 female
    C.S.E. Wistar rats was determined in 5 different vehicles as tabulated
    (Table 2). Most symptoms of acute poisoning developed within 12 hours
    of dosing and were compromised of muscular tremors, hypersensitivity
    to stimuli with dullness and staining of abdominal fur. Most deaths
    occurred between 1 and 3 days (Wallwork & Malone, 1974).

    Table 2: Acute Toxicity of Permethrin (25:75) to Rats in Different
             Vehicles
                                                                        

            Vehicle                                    LD50 (mg/kg)
                                                                        

    110% w/v neat undiluted permethrin [control]       > 20,090
    40% w/v corn oil                                      4,672
    40% w/v petroleum distillate                       >  8,000
    40% w/v dimethyl sulphoxide                        >  8,000
    20% w/v glycerol                                   >  5,048
                                                                        

         The influence of diet on acute toxicity was compared in fed and
    starved rats. Groups of female Sprague-Dawely rats, either fed
     ad libitum or starved for 24 hours beforehand, received a single
    oral dose of permethrin (25:75) (94.1% purity) in corn oil solution
    (40% w/v) at 750, 1500, 3,000 or 6,000 mg/kg. The signs of toxicity
    were similar in fed and starved rats and included body tremor,
    hypersensitivity to sound or touch, splayed gait or walking in tip toe
    and convulsions. Permethrin was more toxic in starved (LD50
    3,000 mg/kg) than in fed animals (LD50 4,251 mg/kg)
    (Piercy et al., 1976).

         The acute dermal toxicity of permethrin (25:75) applied in xylene
    (40% w/v) to female Sprague-Dawley rats exceeded 2,000 mg/kg
    (Harper, et al., 1976). The acute dermal toxicity to male rats
    similarly exceeded 2,000 mg/kg (Harper et al., 1977).

    Short term studies

    Mice

         Groups of six mature female mice received daily oral doses of
    permethrin (25:75) corn oil at 0, 200, 400 and 800 and 1600 mg/kg for
    10 consecutive days. The animals were sacrificed on the 11th day so
    that clinical chemical, hematological parameters and organ weights
    could be recorded.

         Signs of acute toxicity, namely spasm and convulsion were seen
    only in the high dose group, half of which died after the initial
    dose. There were no significant changes observed in hematology,
    clinical chemistry or body weights. The mice treated at 800 and
    1600 mg/kg exhibited increased liver weights
    (Wallwork et al., 1974a).

    Rats

         Groups of 5-6 female Charles River CDI rats received permethrin
    (25:75) in corn oil at 0, 200, 400 or 800 mg/kg by daily savage for
    ten days. The animals were sacrificed on the eleventh day so that
    hematological, clinical chemical parameters and organ weights could be
    investigated.

         At 800 mg/kg, signs of toxicity occurred after each dose and
    4 rats died. At 400 mg/kg, slight muscle fasciculation and
    hypersensitivity to stimuli developed only after the initial two
    doses. Toxicity was not observed at 200 mg/kg. At necropsy, there was
    a dose-related increase in absolute and relative liver weight and
    increase in hepatic aspartate amino-transferase, alanine
    amino-transferase and lactate dehydrogenase activities
    (Wallwork et al., 1974b).

    Rabbits

         Groups of 5 female Dutch rabbits received permethrin (25:75) in
    ten daily doses by savage in corn oil at 0, 200, 400 or 800 mg/kg. The
    animals were necropsied on the eleventh day so that clinical chemical,
    hematological parameters and organ weights could be investigated.

         One rabbit, dosed at 400 mg/kg, exhibited mild hyperactivity and
    muscular fasciculation at days six and seven only. Although all
    animals, including controls, exhibited some degree of weight loss, it
    was most marked in the high-dose group. There were no significant
    hematological or clinical chemistry findings but there was some
    decrease in liver and kidney weight and also some enlargement of
    adrenal gland weights in all treated groups (Chesher & Malone, 1974a).

    Dogs

         Two Beagle dogs received daily oral doses of permethrin (25:75)
    (500 mg/kg) for 14 days. There were no clinical signs of toxicity or
    significant effects of treatment on body weight, clinical chemistry or
    hematological parameters (Chesher et al., 1975a).

         Groups of 4 male and 4 female beagle dogs received encapsulated
    permethrin [(25:75) 4.5% w/v] at 0, 10, 50 or 250 mg/kg for 6 months.
    No signs of toxicity were observed in any group and treatment was
    without effect on body weight. Ophthalmoscopy and electrocardiography
    were unremarkable as were routine hematological, clinical chemistry
    and urinalysis.

         At necropsy, there were no gross pathological or significant
    histopathological findings. Hematological and clinical chemistry
    parameters, including plasma antipyrine elimination rate, were
    unaffected by treatment. The results of this study indicate that daily
    oral doses up to 250 mg/kg did not adversely affect the dogs
    (Reynolds et al., 1978).

    Long term studies

    Rats

         Groups of 60 male and 60 female Wistar SPF rats received 0, 10,
    50 or 250 mg/kg bw/day permethrin (25:75) in their diet for 103
    consecutive weeks. From week 90 onward a low incidence of generalized
    body tremor occurred in high-dose rats but survival was reduced in
    high-dose males only. Body weights and food consumption were not
    affected by treatment. Ophthalmoscopy and hematological, clinical
    chemistry and urinalysis parameters remained within normal limits
    throughout treatment.

         At necropsy, there was a significant increase in absolute and
    relative liver weight of high-dose male rats. Histopathology showed a
    dose-related periacinar hyper-trophy of hepatocytes in mid- and
    high-dose males only. There were no treatment-related increases in
    neoplasms. The results of this study do not indicate any oncogenic
    potential for permethrin and indicate a no-observed effect level of
    10 mg/kg/day (McSheehy & Finn, 1980).

    Observations in humans

         Two human volunteers, who consumed about 2 and 4 mg of permethrin
    (25:75), respectively, excreted 18-37% and 32-39% of the administered
    dose, detected as the metabolite, 3-(2,2-dichlorovinyl)-2,2-dimethyl-
    cyclopropanecarboxylic acid, after acid hydrolysis of their urine
    collected over 24 hours (Cridland & Weatherley, 1977a; Cridland &
    Weatherley, 1977b).

         In a study to assess the degree of dermal absorption of
    permethrin from impregnate clothing, a group of 10 male volunteer
    soldiers wore military clothing for 48 hrs which had been previously
    treated with an aqueous suspension of permethrin (0.2% w/v).
    Subsequent analysis showed that the mean concentration of the uniform
    shirts and trousers was 0.32 g permethrin (25:75)/100 g. However, the
    average individual exposure to permethrin was 3.8 mg/day. No
    volunteers complained of irritancy and there were no findings on
    physical examination (Farquhar et al., 1981a).

         Two of 17 volunteers developed mild erythema when dermally
    exposed to permethrin [(25:75) 1% w/w in soft paraffin] for up to
    9 days using a patch test (Pegum & Doughty, 1978).

         To assess the human tolerance, absorption and persistence of
    permethrin when used as a human pedunculicide (to be used against
    lice), 10 adult volunteers (4 men, 6 women) were treated with 15-40 ml
    of permethrin (25:75) (1%) head louse solution. Their hair was allowed
    to dry naturally and then washed with baby shampoo. Urine samples were
    collected at 0-24, 24-48. 120-144 and 336-360 hrs to permit estimation
    of dermal absorption. On assessment, 3 of 10 volunteers developed
    mild, patchy erythema which faded between days 4-7. Excretion of
    permethrin in the first 24 hours was only about 1% of the applied
    dose, whilst the cumulative maximum was only about 5.5 mg over 14 days
    (Farquhar et al., 1981b).

         As part of a Stage V evaluation of permethrin (25:75) (5% WDP) in
    Nigeria, medical surveillance, including urinalysis of staff engaged
    in bagging, mixing or spraying was undertaken. Medical history, pulse
    and blood pressure were recorded and urine collected twice daily. This
    surveillance revealed no effects attributable to permethrin. Despite
    their use of protective clothing, up to 2 mg of permethrin was
    excreted within 24 hrs of exposure to up to 6 kg of permethrin
    (Rishikesh et al., 1978).

         To assess the safety of permethrin dusts for control of human
    body lice, approximately 350 people were individually dusted with 50 g
    of powder containing either 2.5 or 5.0 g/kg of permethrin. Urine
    samples, taken at the time of treatment and subsequently, indicated
    that maximal absorption of permethrin was 39 g/kg, 24 hr after
    treatment (Nassif et al., 1980).

    COMMENTS

         As noted by the 1982 JMPR, the acute toxicity of permethrin
    (25:75 cis-, trans-) is less than that of permethrin (40:60). On
    short-term administration to rats and mice, permethrin (25:75) was of
    similar toxicity to permethrin (40:60). Permethrin (25:75) is not
    mutagenic in short term tests or in a dominant lethal assay and this
    isomeric mixture is not carcinogenic in mice or rats. It is also not
    teratogenic in, and does not adversely affect the reproduction, of
    rats. Chronic feeding of permethrin (25:75) to rats for 2 years
    increased the liver weights of male rats, as did permethrin (40:60).

         The toxicological profile of permethrin (25:75) thus resembles
    that of permethrin (40:60), although it is less acutely toxic.
    Accordingly, the meeting agreed to extend the previously established
    ADI for permethrin (40:60) to include permethrin (25:75).

    TOXICOLOGICAL EVALUATION

    LEVEL CAUSING NO TOXICOLOGICAL EFFECT (for the nominal 40% cis-, 60%
    trans- and 25% cis-, 75% trans- materials)

         Rat:      100 ppm in the diet, equivalent to 50 mg/kg bw/day

    ESTIMATE OF ACCEPTABLE DAILY INTAKE FOR MAN

         0-0.05 mg/kg bw.

    STUDIES WHICH WILL PROVIDE INFORMATION VALUABLE IN THE CONTINUED
    EVALUATION OF THIS COMPOUND

         Observations in man.

    REFERENCES

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    Chesher, B.C. & Malone, J.C., 1974b. Guinea pig sensitisation study
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    Clive, C.D., 1977. Mutagenicity of BW21Z73 in L51784/TK Mouse
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    Clive, C.D., 1979. Mutagenicity Testing of BW0021Z73 in Salmonella.
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    Cridland, J.S. & Weatherley, B.C., 1977b. An estimate of permethrin
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    See Also:
       Toxicological Abbreviations
       Permethrin (EHC 94, 1990)
       Permethrin (HSG 33, 1989)
       Permethrin (ICSC)
       PERMETHRIN (JECFA Evaluation)
       Permethrin (Pesticide residues in food: 1979 evaluations)
       Permethrin (Pesticide residues in food: 1980 evaluations)
       Permethrin (Pesticide residues in food: 1981 evaluations)
       Permethrin (Pesticide residues in food: 1982 evaluations)
       Permethrin (Pesticide residues in food: 1983 evaluations)
       Permethrin (Pesticide residues in food: 1984 evaluations)
       Permethrin (JMPR Evaluations 1999 Part II Toxicological)
       Permethrin (UKPID)
       Permethrin (IARC Summary & Evaluation, Volume 53, 1991)