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    HEXYTHIAZOX

    First draft prepared by
    Mrs.Dr.E.M. den Tonkelaar,
    Mrs.J.E.M. van Koten-Vermeulen,
    National Institute of Public Health
    and Environmental Protection,
    Bilthoven, The Netherlands

    (4RS,5RS)-5-(4-chlorophenyl)-N-cyclohexyl-4-methyl-2-oxo-
    1,3-thiazolidine-3-carboxamide.

    EXPLANATION

         Hexythiazox is a specific acaricide used in controlling many
    kinds of phytophagous mites. It acts as an ovicide, larvicide and
    nymphicide.  It was reviewed for the first time at the present
    meeting.

    EVALUATION FOR ACCEPTABLE DAILY INTAKE

    Biological data

    Biochemical aspects

    Absorption, distribution and excretion

         Five male and five female CR Fischer rats were given via a
    stomach tube a single oral dose of 10 mg/kg bw [thiazolidine-5-14C]
    hexythiazox (purity >99%) in DMSO. Blood, urine and faeces were
    collected periodically for 72 hours. Rats were sacrificed and tissues
    were collected and analyzed for radioactivity. Maximal plasma
    concentrations were observed 4 hours after dosing (2.22 and 2.55 mg/kg
    in males and females, respectively) and decreased rapidly thereafter
    to approximately 0.1 mg/kg in both sexes after 72 hours. A total of
    30% of the radioactivity was excreted in the urine in both sexes, but
    a slightly larger proportion was eliminated in the faeces of male rats
    (66%) than in female rats (60%).  About 4% and 10% was recovered in
    the carcass and tissues of males and females, respectively. Highest
    tissue concentrations were observed in fat, adrenals and digestive
    organs and their contents, liver and ovaries (Soeda, 1985).

    Biotransformation

         After the oral administration of 10 mg/kg bw [thiazolidine-
    5-14C] hexythiazox to 5 male and 5 female rats (see above), urine and
    faeces were analyzed by HPLC-cochromatography and spectrometry. About
    28% to 60% of the administered radioactivity was excreted in the urine
    and faeces, respectively. Twenty percent of the dose was excreted as
    parent compound, mainly in the faeces.  The main metabolite in urine
    and faeces was 5-(4-chlorophenyl)-N-( cis-4-hydroxylcyclohexyl)-
    4-methyl-trans-2-oxothiazolidine-3-carboxamide {PT-1-8 ( cis)}. A
    number of other metabolites were detected in smaller quantities.  The
    levels of bound 14C-residues were evaluated by polar solvent
    extraction of liver and fat tissue. The largest part of the extracted
    radioactivity in the fat was unchanged parent compound.
    Biotransformation occurred via oxidation of the cyclohexane ring,
    followed by splitting off of this ring and finally of the thiazolidone
    ring. However, only approximately 10% of the radioactivity in the
    urine and 50% in the faeces could be identified. A proposed metabolic
    pathway is given in Figure 1 (Soeda, 1985).

    FIGURE 1

    Toxicological studies

    Acute toxicity

         The LD50 and LC50 for hexythiazox, the 10% WP formulation and
    certain metabolites, are given in Tables 1, 2 and 3, respectively.

         No signs of toxicity were observed after acute oral and dermal
    exposure to hexythiazox.

    Short-term studies

    Mice

         Male and female B6C3F1 mice (10/sex/group) were fed diets
    containing 0, 50, 300, 1800 or 10 800 ppm hexythiazox (purity 98.3%)
    for 28 days.  No compound-related effects were observed on mortality,
    clinical signs, food consumption and food efficiency, haematology, nor
    macroscopy.  Male body weight gain was decreased at 1800 and 10 800
    ppm hexythiazox.  Total cholesterol levels decreased in male and
    female mice at 10 800 ppm and in males also at 1800 ppm.  Urine
    specific gravity was increased in high-dose males.  Relative liver
    weight was increased in male and female mice at 1800 and 10 800 ppm. 
    At histopathology an increased incidence of swollen liver cells was
    observed in high-dose males (also at 1800 ppm) and females.  The NOAEL
    in this study is 300 ppm, equal to 55.1 mg/kg bw (males) and 62.9
    mg/kg bw (females) (Takaori & Nishibe, 1983a).

    Rats

         Groups of Fischer rats (20/sex/group) received a diet containing
    0, 10, 70, 500 or 3500 ppm hexythiazox (98.3%) for 13 weeks. 
    Observations included clinical signs, food and water consumption,
    haematology, biochemistry, cholinesterase activity, urinalysis,
    macroscopy, organ weights and histopathology.  Growth was depressed in
    both sexes at 3500 ppm and in females also at 500 ppm.  In high-dose
    males Hb, PCV, RBC and MCV were decreased and platelet count was
    increased.  In high-dose females MCHC and MCH (also at 500 ppm) were
    decreased. At 3500 ppm hexythiazox total cholesterol, albumin (in
    males also at 500 ppm), protein and calcium were increased in both
    sexes. ALP and ASAT were increased in high-dose females. Protein in
    urine was increased in males at 3500 ppm. Relative liver (also at 500
    ppm), kidney, adrenal and gonad weight were increased and spleen
    weight decreased at 3500 ppm in both sexes. At 70 ppm liver weight was
    still slightly increased in females. Female brain weight was increased
    at 500 and 3500 ppm. At histopathology swelling of hepatocytes in the
    central zone was observed in both sexes at the highest dose.  Fatty
    degeneration of the  zona fasciculata of the adrenal cortex was
    observed at dose levels of 500 ppm and greater. The NOAEL is 70 ppm,
    equal to 8.1 mg/kg bw/day (males) and 5.3 mg/kg bw/day (females)
    (Takaori & Nishibe, 1983b).


        Table 1.  Acute toxicity of hexythiazox

                                                                                                           

    Species         Sex         Route       Purity      LD50        LC50       References
                                                     (mg/kg bw)    (mg/l)
                                                                                                           

    Mouse           M&F         oral         98.3%     > 5000                  Saika & Nishibe (1983a)
                    M&F         s.c.         98.2%     > 5000                  Inoue (1987a)
                    M&F         i.p.         98.2%     > 5000                  Inoue (1987b)

    Rat             M&F         oral         98.3%     > 5000                  Saika & Nishibe (1983b)
                    M&F         s.c.         98.2%     > 5000                  Inoue (1987c)
                    M&F         i.p.         98.2%     > 5000                  Inoue (1985)
                    M&F        inhl.a        98.3%                  > 2.0      Saika & Nishibe (1983c)
                    M&F        dermal        98.3%     > 5000                  Saika & Nishibe (1983d)

    Dog             M&F         oral         98.3%     > 5000                  Saika & Nishibe (1984)
                                                                                                           

    a   4 hour exposure

    Table 2.  Acute toxicity of 10% wettable powder of hexythiazox

                                                                                                           

    Species         Sex         Route       Purity      LD50        LC50       References
                                                     (mg/kg bw)    (mg/l)
                                                                                                           

    Rat             M&F         oral                   > 5000                  Saika & Nishibe (1983e)
                    M&F        inhal.a                              > 2.9      Saika & Nishibe (1983f)
                    M&F        dermal                  > 5000                  Saika & Nishibe (1983g)
                                                                                                           

    a   4 hour exposure

    Table 3.  Acute toxicity of metabolites of hexythiazox in rats

                                                                                            

    Metabolite      Sex         Route       Purity      LD50        References
                                                     (mg/kg bw)
                                                                                            

    PT-1-2           M          oral         > 99%      2321        Saika & Nishibe (1985)
                     F                                  1079

    PT-1-3           M          oral         > 99%       494        Saika & Nishibe (1985)
                     F                                   341

    PT-1-4          M&F         oral         > 99%     > 5000       Saika & Nishibe (1985)
    (trans-2)

    PT-1-8          M&F         oral         > 99%     > 5000       Saika & Nishibe (1985)
    (trans)

    PT-1-8          M&F         oral         > 99%     > 5000       Saika & Nishibe (1985)
    (cis)
                                                                                            
    

    Dogs

         In a range-finding study groups of Beagle dogs (2/sex/group) were
    fed diets containing 0, 125, 500, 2000 or 8000 ppm hexythiazox (purity
    97.7%) for 4 weeks.  No effects were observed on clinical signs nor
    mortality.  Body weight gain was decreased in females and food
    consumption in males at 8000 ppm. Relative liver weight was increased
    in females at 2000 and 8000 ppm and slightly increased in high-dose
    males (Spicer, 1984a).

         Male and female Beagle dogs (4/sex/group) received a diet
    containing 0, 100, 500 or 5000 ppm hexythiazox (purity 97.7%) for 12
    months.  Observations were made for clinical signs, body weight, food
    consumption and food efficiency, ophthalmology, haematology,
    biochemistry, cholinesterase activity and urinalysis. The weights of
    10 organs/animal were recorded. Gross necropsy and histo-pathology
    were carried out.  ALP was increased in both sexes at 5000 ppm and
    ALAT was increased in females at the same dose. Total protein was
    decreased in males at 500 and 5000 ppm and in females at 5000 ppm. 
    Phosphorus was decreased in females 500 and 5000 ppm.  Relative
    adrenal weight was increased in high-dose dogs and relative liver
    weight was increased in high-dose males.  At histopathology
    adrenocortical hypertrophy occurred in male and female dogs at 500 and
    5000 ppm. Hepatocellular hypertrophy was observed in high-dose dogs.
    The NOAEL in this study is 100 ppm, equal to 2.87 mg/kg (males) and
    3.17 mg/kg (females) (Spicer, 1984b).

    Long-term/carcinogenicity studies

    Mice

         Groups of B6C3F1 mice (50/sex/group) received a diet
    containing 0, 40, 250 or 1500 ppm hexythiazox (purity 98.2%) for 104
    weeks. An additional 30 mice (10/sex/group) served for the collection
    of blood samples after 26, 52 and 79 weeks.  Observations included
    clinical signs, mortality, body weight, food consumption and food
    efficiency, haematology, clinical chemistry, urinalysis, macroscopy,
    organ weight (after 26, 52, 78 and 104 weeks) and histopathology
    (after 52 and 104 weeks).  Body weight gain and absolute body weights
    were decreased at 250 and 1500 ppm in male mice only. During the
    second half of the study body weight gain was also significantly
    decreased at 40 ppm.  Various red blood cell parameters were decreased
    during the first 78 weeks at the highest dose.  Relative liver weight
    was increased in males and females at 1500 ppm during the whole study. 
    After 104 weeks relative weights of brain, heart, kidneys, adrenals
    and testes were increased in male mice.  Relative brain, kidneys,
    adrenals and testes weight were increased in males at 250 ppm. 
    Histopathology of the liver after 52 weeks showed an increased
    incidence of fatty degeneration and hypertrophy of the hepatocytes
    with nuclear pleomorphism in males at 1500 ppm which was only

    marginally increased at 250 ppm. At the end of the study the incidence
    of hyperplastic nodes consisting of proliferating hepatocytes was
    increased in both sexes at the highest dose (incidences (52+104 weeks
    60 rats): 20%, 20%, 25% and 50% for males and 5%, 8%, 6% and 27% for
    females at 0, 40, 250, and 1500 ppm, respectively).  At the same dose
    an increase in the incidence of hepatocellular adenomas or carcinomas
    was also observed (incidences: adenomas: 20%, 25%, 20% and 33% for
    males and 10%, 2%, 5% and 17% for females; carcinomas: 13%, 13%, 17%
    and 13% for males and 0%, 5%, 5% and 8% for females both at 0, 40,
    250, and 1500 ppm hexythiazox). In 3 males at 1500 ppm
    haemangiopericytoma was observed in the liver.  This incidence was
    within the historical control range.  At the lowest dose level of 40
    ppm (equal to 6.7 in males and 8.4 in females) there was still a
    decreased body weight gain (Inoue & Enomoto, 1984).

         Because of the observed increase of liver tumours an additional
    histological examination was performed on the livers of mice
    (10/sex/group) sacrificed after 78 weeks. In high-dose females the
    incidence of nuclear pleomorphism of the liver cells and fatty
    degeneration were increased. The tumour incidences were not enhanced
    (Enomoto, 1985).

    Rats

         Groups of Fischer 344 rats (50/sex/group) were fed diets
    containing 0, 60, 430, or 3000 ppm hexythiazox (purity 99%) for 104
    weeks. Additional groups of 10 rats/sex/group were treated at the same
    dose levels and were used for interim sacrifice at 12 months.  The
    observations included clinical signs, body weight, food consumption,
    ophthalmology, haematology, biochemistry, urinalysis, macroscopy,
    organ weight and histopathology.  At the end of the study the
    incidence of internal abdominal masses and swollen testicles and
    non-descended testicles was high in all males but was observed to a
    greater degree at 430 and 3000 ppm hexythiazox. Mean body weight was
    decreased in high dose males and females and slightly at 430 ppm. Food
    consumption was increased in both sexes at 3000 ppm and in females at
    430 ppm. ALP, ALAT, ASAT and potassium levels were decreased in
    high-dose females. At the end of the study most relative organ weights
    (including the liver) were increased in both sexes at 3000 ppm.  At
    430 ppm relative brain, heart, lung and spleen weights were still
    increased in males.  No treatment-related histopathological changes
    were observed.  The tumour incidence was not enhanced. The NOAEL in
    this study is 60 ppm, equal to 3.2 mg/kg bw (males) and 4.02 mg/kg bw
    (females) (Spicer, 1984c).

    Reproduction studies

         In a two-generation reproduction study (2 litters/generation)
    groups of SPF Wistar rats (30/sex/group) were given diets containing
    0, 60, 400 or 2400 ppm hexythiazox (purity 98.2%).  Observations
    included clinical signs, body weight, food consumption, food

    efficiency, reproductive findings, organ weight and histopathology. 
    Five dams/group were sacrificed on day 21 of pregnancy for teratogenic
    examinations.

         Body weight and food consumption were decreased in high dose F0
    parents.  An increased number of delivered F1 pups was observed in
    the second mating at 400 and 2400 ppm hexythiazox.  At 400 and 2400
    ppm the relative weights of liver, kidney, adrenals (only at 2400 ppm)
    and testes (no dose relationship) were increased in F0 adults.  A
    tendency to an increased mean number of implantations and total
    resorptions was observed in the F0 generation at 400 and 2400 ppm. 
    At histopathology a higher incidence of proteinaceous casts in the
    kidneys was observed in F0 male rats at 2400 ppm.  The number of live
    born F1b pups was increased at 400 and 2400 ppm and pup weight was
    decreased from day 4 to 28 of lactation at these dose levels.  A delay
    in hairgrowth of abdomen was observed in pups at all treated groups of
    the first generation.  In F1 parents, body weight was decreased at
    2400 ppm and in males occasionally also at 400 ppm.  Food consumption
    was decreased at the highest dose. The mean number of implants,
    implants/corpora lutea and number of live fetuses were increased in
    the 2400 ppm F1 group.  Relative weights of brain (males only),
    liver, kidneys, adrenals (males only) and ovaries were increased in
    high dose F1 parents. F2b pup weight was decreased at 2400 ppm
    hexythiazox.  A delay in abdominal hair growth and eye-opening were
    observed in F2b pups at 2400 ppm. Body weight and food consumption
    (females only) of F1 adults were decreased at the highest dose. F1
    adults showed an increased relative weight of ovaries, adrenal, liver
    and kidney (males only) and showed a decreased spleen weight at 2400
    ppm. Liver and kidney weight were also increased in males at 400 ppm.
    An increase in the appearance of proteinaceous casts was observed in
    the kidneys of high-dose males.  Malformations were not observed.  The
    NOAEL in this study is 60 ppm (equal to a range between 4.22 and 5.34
    mg/kg bw, depending on sex and generation) (Okugi & Enomoto, 1984).

    Special studies on embryotoxicity and/or teratogenicity

    Rats

         Pregnant Sprague-Dawley rats (24/group) received by gavage 0,
    240, 720 or 2160 mg hexythiazox (purity 98.3%)/kg bw from day 7
    through 17 of gestation.  The rats were sacrificed on day 21. 
    Observations were made for body weight, food and water consumption,
    number of implantations, number of live and dead fetuses, number of
    early and late resorptions and number of corpora lutea.  The fetuses
    were weighed and examined for external, visceral and skeletal
    abnormalities. Female body weight gain and occasionally food
    consumption were decreased at 720 and 2160 mg/kg bw/day.  Relative
    ovarian weight was increased at the two highest dose levels. The
    ossification of the metatarsal bones was significantly delayed at 720
    and 2160 mg/kg bw/day.  The NOAEL for maternal and embryotoxicity was
    240 mg/kg bw/day.  There was no evidence for hexythiazox-induced
    irreversible structural effects (Gotoh & Nishibe, 1983).

    Rabbits

         Four groups of 15 pregnant New Zealand white rabbits received by
    gavage 0, 120, 360, or 1080 mg hexythiazox (purity 97.7%)/kg from day
    6 to 18 of gestation.  All dams were sacrificed on day 28 of
    gestation.  No significant changes were observed in mortality,
    maternal body weight and food consumption, uterus weight, number and
    location of viable fetuses, early and late resorptions, number of
    total implantations nor corpora lutea and organ weight. Two dams died,
    1 at 120 mg/kg bw/day and 1 at 360 mg/kg bw/day.  A slightly greater
    number of fetuses with skeletal variations (overlapping of the
    vertebral arch, asymmetry of the sternebrae) was observed at 1080
    mg/kg bw/day.  The NOAEL in this study is 360 mg/kg bw/day.  No
    irreversible structural effects were observed (Gotoh & Nihsibe, 1984).

    Special studies on mutagenicity

         Hexythiazox was negative in various mutagenicity assays (see
    Table 1). Ames tests were conducted with 8 plant metabolites (some
    also occurring in the rat): PT-1-2. PT-1-3, PT-1-4( trans-2),
    PT-1-5(1), PT-1-6( trans-2), PT-1-8( cis), (PT-1-8( trans) and
    PT-1-9.  All metabolites gave negative results in the tests using
     S. typhimurium (TA1535, TA100, TA1538, TA98 and TA1537) as well as
     Escherichia coli (WP2 uvra) (Sasaki & Nishibe, 1985).

    Special studies on pharmacology

    Mice

         Doses > 1000 mg hexythiazox (purity 98.3%) given
    intraperitoneally to 3 male S1c:ddY mice delayed the sleeping time
    induced by sodium pentobarbital.  Effects were observed as soon as 15
    minutes after hexythiazox administration.  Hexythiazox also prolonged
    the time at which convulsions induced by pentetrazole or strychnine
    began.  Intestinal motility and gastric secretion in mice were not
    affected by the administration of up to 150 mg hexythiazox iv nor up
    to 3000 mg/kg (oral), respectively (Souma & Nishibe, 1985).

    Rats

         Blood coagulation time in S1c:Wistar rats was decreased after
    administration of 3000 mg hexythiazox in saline, but haemolysis was
    not observed. I.p. administration of doses as high as 2500 mg
    hexythiazox/kg had no effect on rat body temperature nor on gastric
    secretion. No effect on the tension of the muscle twitch induced by
    the indirect stimulation was observed after i.v. injection of 50 or
    100 mg hexythiazox/kg (Souma & Nishibe, 1985).


    
    Table 4.  Results of mutagenicity assays on hexythiazox

                                                                                                                     

    Test system            Test object           Concentration        Purity (%)      Results      References

                                                                                                                     

    In vitro

    Ames testa,b           S. typhimurium        100-6400 g/plate       97.7         Negative     Inoue (1983a)
                           TA 100, TA98,         in DMSO
                           TA1535, TA1537,
                           TA1538
                           E coli, WP2 uvra

    Yeast testa,b          S. cerevisiae         312-10 000 g/ml        98.4         Negative     Jagannath (1984)
    (reverse mutation)     S138, S211            in DMSO
    (mitotic gene          S. cerevisiae         1-10 000 g/plate       98.4         Negative
    conversion)            D4

    V79/HGPRTa,b           Chinese hamster       9.38-150 g/ml          98.6         Negative     Seeberg (1986)
    mutation assay         V79 cells             in DMSO

    Chromosome             Chinese hamster       1.5-50 g/ml            98.4         Negative     Galloway (1984)
    aberration             ovary cells
    assaya

    Rec-assay              B. subtilis           400-3200 g/plate       97.7         Negative     Inoue (1983b)
                           H17(rec+)             in DMSO
                           M45(rec-)

    Unscheduled DNA        Rat hepatocytes       2.5-100 g/ml           98.4         Negative     Cifone (1985)
    synthesis              (250 g/ml lethal)
                                                                                                                     

    Table 4 (contd).

                                                                                                                     

    Test system            Test object           Concentration        Purity (%)      Results      References

                                                                                                                     

    In vivo

    Cytogenic testa,b      Chinese hamster       1000, 2000 or 4000      98.6         Negative     Mosesso (1986)
                           bone marrow           mg/kg p.o.

    Micronucleus test      Male and female       0.1, 0.5 and 1.0        98.4         Negative     Ivett (1984)
                           CD-1 bone marrow      g/kg p.o.
                           cells
                                                                                                                     

    a  without metabolic activation
    b  with metabolic activation
    

    Rabbits

         Hypotension and hypoventilation were observed after the iv
    injection of 50 mg hexythiazox/kg once weekly (Souma & Nishibe, 1985).

    Guinea-pig

         High concentrations of hexythiazox inhibited the contraction of
    isolated ileum induced by acetylcholine, histamine and barium chloride
    (Souma & Nishibe, 1985).

    Special studies on sensitization

         Hexythiazox (purity 98.3%) as well as a 10% WP formulation did
    not exhibit a sensitizing effect in the maximization test (Magnusson
    & Kligman) in female Hartley guinea-pigs (Souma & Nishibe, 1983a;
    1983d).

    Special studies on skin and eye irritation

         A dose of 0.5 g hexythiazox (purity 98.3%) and a 10% WP
    formulation moistened with water was applied under occlusive
    conditions to the clipped back skin of 6 male New Zealand White
    rabbits for 4 hours.  No skin irritation was observed up to 72 hours
    after application (Souma & Nishibe, 1983b; 1983e).

         Applications of 0.1 g hexythiazox (purity 98.3%) and a 10% WP
    formulation into the eyes of 6 male New Zealand White rabbits caused
    slight irritation (redness of the conjunctivae).  No irritation
    effects were observed 48 hours post-application (Souma & Nishibe,
    1983c; 1983f).

    Observation in humans

         Health examinations (twice a year) were performed on a group of
    16 to 26 workers in a Japanese manufacturing plant. The health
    examination consisted of analysis for gamma-GTP (once a year), Hb,
    haematocrit, erythrocytes and urinalysis (protein, glucose and
    urobilinogen). No adverse effects were observed on the examined
    parameters after three years of continuous exposure to hexythiazox
    (Motogi, 1987).

    COMMENTS

         After oral administration to rats, hexythiazox was eliminated
    rapidly, two-thirds via the faeces and one-third via the urine.  Low
    levels were recovered in the tissues and organs, with the highest
    concentrations in the fat, liver, adrenals and in the gastrointestinal
    tract and its contents. In the faeces about 20% was excreted as the
    parent compound.  Many metabolites were found in the urine and faeces,
    although only 10% of those in the urine and 50% of those in the faeces
    could be identified. Metabolism occurs via oxidation, and finally
    cleavage, of the cyclohexane ring.

         The compound shows low acute toxicity in the species examined. 
    WHO has classified hexythiazox as unlikely to present acute hazard in
    normal use.

         Short-term administration of hexythiazox to rats and dogs
    revealed the liver and the adrenals as target organs. In a 90-day
    study in rats the NOAEL was 70 ppm, equal to 4.9 and 5.3 mg/kg bw/day
    for males and females respectively.  In a one-year study in dogs the
    NOAEL was 100 ppm, equal to 2.9 mg/kg bw/day in males and 3.2 mg/kg
    bw/day in females.

         In a 2-year feeding study in mice at dietary concentrations of 0,
    40, 250, or 1500 ppm there was an increased incidence of liver nodules
    in both sexes at 1500 ppm.  The incidences of liver adenomas and
    hepatocarcinomas were increased in females at 1500 ppm. Three
    haemangiopericytomas in the liver were observed in males at 1500 ppm. 
    These were subsequently re-evaluated as hepatoblastomas.  At the
    lowest concentration of 40 ppm, equal to 6.7 and 8.4 mg/kg bw/day in
    males and females respectively, reduced body-weight gain in male
    animals was observed.  A NOAEL was not established.

         In a long-term carcinogenicity study in rats at dietary
    concentrations of 0, 60, 430, or 3000 ppm, there were no
    treatment-related increases in neoplasias.  There was a reduction in
    body-weight gain and an increase in some organ weights at 430 ppm. 
    The NOAEL was 60 ppm, equal to 3.2 and 4.2 mg/kg bw/day for males and
    females respectively.

         In a 2-generation, 2-litters-per-generation reproduction study in
    rats at 0, 60, 400, or 2400 ppm, no adverse effects on reproduction
    were found.  The NOAEL was 60 ppm, equivalent to 3 mg/kg bw/day, based
    on increased liver and kidney weights at 400 ppm.

         Maternal toxicity (reduced weight gains) and embryotoxicity
    (delayed development) were observed in a teratogenicity study in rats
    at doses of 0, 240, 720, or 2160 mg/kg bw/day.  The NOAEL was 240
    mg/kg bw/day.  In a teratogenicity study in rabbits at doses of 0,
    120, 360 or 1080 mg/kg bw/day, slight embryotoxicity was observed at

    the highest dose.  The NOAEL was 360 mg/kg bw/day.  No teratogenic
    effects were observed in either species.

         After reviewing all available  in vitro and  in vivo short-term
    tests on hexythiazox it was concluded that there was no evidence of
    genotoxicity.

         An ADI was established which was based on NOAELs in the 2-year
    feeding and reproduction studies in rats and a 1-year study in dogs,
    using a 100-fold safety factor.

    TOXICOLOGICAL EVALUATION

    Level causing no toxicological effect

         Rat:      60 ppm in the diet, equal to 3.2 mg/kg bw/day
                   (2-year study)
         Rat:      60 ppm in the diet, equivalent to 3 mg/kg bw/day
                   (reproduction study)
         Dog:      100 ppm in the diet, equal to 2.9 mg/kg bw/day

    Estimate of acceptable daily intake for humans

         0-0.03 mg/kg bw

    Studies which will provide information valuable in the
    continued evaluation of the compound

         Observations in humans.

    REFERENCES

    Cifone, M.A. (1985)  Evaluation of NA-73 technical lot no. SCF-05 in
    the rat primary hepatocyte unscheduled DNA synthesis assay.
    Unpublished second amended report 20991 (RD-8556) from Litton
    Bionetics, Inc. Kensington, Maryland, USA.  Submitted to WHO by Nippon
    Soda Ltd. Tokyo, Japan.

    Enomoto, M. (1985)  Supplement to the chronic feeding and oncogenicity
    studies in mice with NA-73. Histological findings of the liver of mice
    sacrificed at 78 weeks. Unpublished Report 527 (RD-8534) from
    Biosafety Research Center, Foods, Drugs and Pesticides (AN-PYO
    Center). Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Galloway, S.M. (1984)  Mutagenic evaluation of NA-73 Technical lot no.
    SCF-05. in an  in vitro cytogenetic assay measuring chromosome
    aberration frequencies in Chinese hamster ovary (CHO) cells.
    Unpublished amended report 20990 (RD-8435N) from Litton Bionetics,
    Inc. Kensington, Maryland 20895, USA. Submitted to WHO by Nippon Soda
    Ltd. Tokyo, Japan.

    Gotoh, K. & Nishibe, T. (1983)  Teratogenicity study of NA-73 in rats.
    Unpublished toxicology report 0118 (RD-83104) from Biomedical research
    department of Nisso Institute for Life Science.  Submitted to WHO by
    Nippon Soda Ltd. Tokyo, Japan.

    Gotoh, K. & Nishibe, T. (1984)  Teratogenicity study of NA-73 in
    rabbits. Unpublished toxicology report 0126 (RD-8454) from Biomedical
    Research Department of Nisso Institute for Life Science. Submitted to
    WHO by Nippon Soda Ltd. Tokyo, Japan.

    Inoue, H. (1983a)  NA-73: Mutagenicity test in bacteria. Unpublished
    Report 364 (RD-83107) from Biosafety Research Center, Foods, Drugs and
    Pesticides (AN-PYO Center).  Submitted to WHO by Nippon Soda Ltd.
    Tokyo, Japan.

    Inoue, H. (1983b)  NA-73: Rec-assay with  Bacillus subtilis strains
    H 17 (rec+) and M 45-). Unpublished Report 363 (RD-83106) from
    Biosafety Research Center, Foods, Drugs and Pesticides (AN-PYO
    Center). Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Inoue, H. (1985)  Acute intraperitoneal toxicity study in rats with
    NA-73. Unpublished Report 623 (RD-8582) from Biosafety Research
    Center, Foods, Drugs and Pesticides (AN-PYO Center), Japan. Submitted
    to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Inoue, H. (1987a)  Acute subcutaneous toxicity study in mice with
    NA-73. Unpublished Report 989 (RD-8759) from Biosafety Research
    Center, Foods, Drugs and Pesticides (AN-PYO Center), Japan. Submitted
    to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Inoue, H. (1987b)  Acute intraperitoneal toxicity study in mice with
    NA-73. Unpublished Report 990 (RD-8758) from Biosafety Research
    Center, Foods, Drugs and Pesticides (AN-PYO Center), Japan. Submitted
    to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Inoue, H. (1987c)  Acute subcutaneous toxicity study in rats with
    NA-73. Unpublished Report 991 (RD-8757) from Biosafety Research
    Center, Foods, Drugs and Pesticides (AN-PYO Center), Japan. Submitted
    to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Inoue, H & Enomoto, M. (1984)  Chronic feeding and oncogenicity
    studies in mice with NA-73. Unpublished Report 483 (RD-84107) from
    Biosafety Research Center, Foods, Drugs and Pesticides (AN-PYO
    Center), Japan. Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Ivett, J.L. (1984)  Mutagenicity evaluation of NA-73 technical in the
     in vivo mouse micronucleus assay. Unpublished Report 20996
    (RD-8436N) from Litton Bionetics, Inc. Kensington, Maryland, USA.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Jagannath, D.R. (1984) Mutagenicity evaluation of NA-73 in the mitotic
    gene conversion and reverse mutation induction in yeast strains D4,
    S138 and S211 plate test.  Litton Bionetics, Inc.  Submitted to WHO by
    Nippon Soda Co. Ltd., Tokyo, Japan.  Unpublished Report RD-8434N.

    Mosesso, P. (1986)  Chinese hamster bone marrow metaphase analysis
    ( in vivo cytogenetics). Test substance: NA 73. Unpublished LSR-RTC
    Report 063015-M-04086 (RD-8696) from Life Science Research Roma
    Toxicology Centre. Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Motogi, S. (1987)  Human handling experiences from plant employees in
    hexythiazox production. Unpublished Report (RD-8749) from
    Environmental Control and Safety Department, Nihongi Plant, Japan.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Okugi, M. & Enomoto, M. (1984)  NA-73: Two-generation reproduction
    study in rats (experiment 221). Unpublished Report 453 (RD-84108) from
    Biosafety Research Center, Foods, Drugs and Pesticides (AN-PYO
    Center), Japan. Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1983a)  Acute oral toxicity study of NA-73 in
    mice. Unpublished toxicology report 0107 (RD-8393) from Biomedical
    Research Department, Nisso Institute for Life Science. Submitted to
    WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1983b)  Acute oral toxicity study of NA-73 in
    rats. Unpublished toxicology report 0092 (RD-8394) from Biomedical
    Research Department, Nisso Institute for Life Science. Submitted to
    WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1983c)  Acute inhalation toxicity study of
    NA-73 in rats. Unpublished toxicology report 0094 (RD-8396) from
    Biomedical Research Department, Nisso Institute for Life Science.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1983d)  Acute dermal toxicity study of NA-73
    in rats. Unpublished toxicology report 0093 (RD-8395) from Biomedical
    Research Department, Nisso Institute for Life Science. Submitted to
    WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1983e)  Acute oral toxicity study of NA-73
    10% WP in rats. Unpublished toxicology report 0123 (RD-83112) from
    Biomedical Research Department, Nisso Institute for Life Science.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1983f)  Acute inhalation toxicity study of
    NA-73 10% WP in rats. Unpublished toxicology report 0121 (RD-83114)
    from Biomedical Research Department, Nisso Institute for Life Science.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1983g)  Acute dermal toxicity study of NA-73
    10% WP in rats. Unpublished toxicology report 0119 (RD-83113) from
    Biomedical Research Department, Nisso institute for life science.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1984)  Acute oral toxicity study of NA-73 in
    dogs. Unpublished toxicology report 0125 (RD-8428) from Biomedical
    Research Department, Nisso Institute for Life Science. Submitted to
    WHO by Nippon Soda Ltd. Tokyo, Japan.

    Saika, O. & Nishibe, T. (1985)  Acute oral toxicity study of main
    metabolites of NA-73 in Rats. Unpublished report 0181 (RD-8570) from
    Toxicology Group, Nippon Soda Ltd. Submitted to WHO by Nippon Soda
    Ltd. Tokyo, Japan.

    Sasaki, T. & Nishibe, T. (1985)  Reverse mutation study of main
    metabolites of NA-73. Unpublished Report 0185 (RD-8571) from
    Toxicology Group, Soda Ltd. Submitted to WHO by Nippon Soda Ltd.
    Tokyo, Japan.

    Seeberg, A.H. (1986)  Gene mutation in Chinese hamster V79 cells test
    substance: NA 73. Unpublished Report 063014-M-03986 (RD-8695) from
    Life Science Research Roma Toxicology Centre. Submitted to WHO by
    Nippon Soda Ltd. Tokyo, Japan.

    Soeda, Y. (1985)  Metabolism of NA-73 in rats (group B). Unpublished
    Report EC-9 (RD-8520N) from Environmental Toxicology Laboratory of
    Nippon Soda Ltd. Submitted to WHO by Nippon Soda Co., Ltd. Tokyo,
    Japan.

    Souma, S. & Nishibe, T. (1983a)  Delayed contact hypersensitivity
    study of NA-73 in guinea pigs. Unpublished toxicology report 0097
    (RD-8399) from Biomedical Research Department, Nisso Institute for
    Life Science. Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Souma, S. & Nishibe, T. (1983b)  Primary dermal irritation study of
    NA-73 in rabbits. Unpublished toxicology report 0095 (RD-8398) from
    Biomedical Research Department, Nisso Institute for Life Science.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Souma, S. & Nishibe, T. (1983c)  Primary eye irritation study of NA-73
    in rabbits. Unpublished toxicology report 0096 (RD-8397) from
    Biomedical Research Department, Nisso Institute for Life Science.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Souma, S. & Nishibe, T. (1983d)  Delayed contact hypersensitivity
    study of NA-73 10%WP in guinea pigs. Unpublished toxicology report
    (RD-83117) from Bio-medical Research Department, Nisso Institute for
    Life Science. Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Souma, S. & Nishibe, T. (1983e)  Primary dermal irritation study of
    NA-73 in rabbits. Unpublished toxicology report (RD-83116) from
    Biomedical Research Department, Nisso Institute for Life Science.
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Souma, S. & Nishibe, T. (1983f)  Primary eye irritation study of NA-73
    in rabbits. Unpublished toxicology report (RD-83115) from Biomedical
    Research Department, Nisso Institute for Life Science. Submitted to
    WHO by Nippon Soda Ltd. Tokyo, Japan.

    Souma, S. & Nishibe, T. (1985)  General pharmacology study of NA-73.
    Unpublished toxicology report 0186 (RD-85104) from Environmental
    Toxicology Laboratory, Nippon Soda Co., Ltd. Submitted to WHO by
    Nippon Soda Ltd. Tokyo, Japan.

    Spicer, E.J.F. (1984a)  Four week dietary range-finding study in dogs
    with NA-73. Unpublished Report (RD-84105) from International Research
    and Development Corporation, Michigan USA. Submitted to WHO by Nippon
    Soda Ltd. Tokyo, Japan.

    Spicer, E.J.F. (1984b)  One year dietary study of NA-73 in dogs.
    Unpublished Report (RD-8433) from International Research and
    Development Corporation, Michigan USA. Submitted to WHO by Nippon Soda
    Ltd. Tokyo, Japan.

    Spicer, E.J.F. (1984c)  Lifetime (24-month) dietary toxicity and
    oncogenicity study of NA-73 in rats. Unpublished Report (RD-84106)
    from International Research and Development Corporation, Michigan USA. 
    Submitted to WHO by Nippon Soda Ltd. Tokyo, Japan.

    Takaori, H. & Nishibe, T. (1983a)  Cumulative toxicity study of NA-73
    in mice. Unpublished Report (RD-83100) from Biomedical Research
    Department, Nisso Institute for Life Science, Japan.  Submitted to WHO
    by Nippon Soda Ltd. Tokyo, Japan.

    Takaori, H. & Nishibe, T. (1983b)  Subchronic feeding study of NA-73
    in rats. Unpublished Report (RD-83101) from Biomedical Research
    Department, Nisso Institute for Life Science, Japan. Submitted to WHO
    by Nippon Soda Ltd. Tokyo, Japan.


    See Also:
       Toxicological Abbreviations