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    CAPTAN (addendum)

    First draft prepared by
    J.-J. Larsen

    Institute of Toxicology, National Food Agency of Denmark, Ministry of
    Health, Soborg, Denmark

    Evaluation for acceptable daily intake
         Biochemical aspects
              Absorption, distribution, and excretion
              Biotransformation
         Toxicological studies
              Short-term toxicity
              Genotoxicity
    Comments
    Toxicological evaluation
    References

    Explanation

         Captan was evaluated toxicologically by the Joint Meeting in
    1963, 1965, 1969, 1973, 1977, 1978, 1982, 1984, and 1990 (Annex I,
    references 2, 3, 12, 20, 28, 30, 38, 42, and 59). Toxicological
    monographs were prepared in 1963, 1965, and 1969 (Annex I, references
    2, 4, and 13), and monograph addenda were prepared in 1973, 1977,
    1978, 1982, 1984, and 1990 (Annex I, references 21, 29, 31, 39, 43,
    and 61). Additional information on distribution, excretion, bio-
    transformation, genotoxicity, and short-term toxicity are reviewed in
    this monograph addendum.

    Evaluation for acceptable daily intake

    1.  Biochemical aspects

    (a)  Absorption, distribution, and excretion

         The tissue distribution and excretion of a single oral dose of
    10 mg/kg bw [14C-cyclohexene ring]-labelled captan was studied in
    five male and five female Sprague-Dawley rats (weighing 202-243 g),
    obtained from Charles River, Margate, Kent, United Kingdom. Urinary
    and faecal excretion of radiolabel was monitored over seven days, and
    the residual concentrations of radiolabel were then measured in
    selected tissues. The excretion profiles were similar for male and
    female rats, the urinary route predominating in animals of each sex;
    81% of the administered radioactivity was excreted in the urine and
    8-9% in the faeces over 48 h, and 69-73% in the urine and 23-25% in
    the faeces over 96 h. The residual concentrations in the tissue were
    negligible, the highest concentrations occurring in the kidneys
    (< 0.01% of the total radiolabel) after 48 h and in the blood (about
    2 Ág equivalents of captan per gram) after 96 h (Trivedi, 1990a,b)

         The effect of oral pretreatment with 10 mg/kg bw unlabelled
    captan for 14 days before an oral dose of 10 mg/kg bw [14C-
    cyclohexene ring]-labelled captan was studied in eight male and eight
    female Sprague-Dawley rats (weighing 192-260 g), obtained from Charles
    River, Margate, Kent, United Kingdom. The urinary and faecal excretion
    of radiolabel was monitored over seven days, and the residual
    concentrations of radiolabel were then measured in selected tissues.
    The excretion profiles of male and female rats were similar, the
    urinary route predominating: 88-91% of the administered radiolabel
    in the urine and 7-9% in the faeces over 48 h. The residual
    concentrations in tissues were neglible in animals of each sex, the
    highest concentrations occurring in the kidneys (0.04 Ág/g). The
    pretreatment thus had little or no effect on the route or rate of
    elimination of radiolabelled substance (Bratt, 1990).

    (b)  Biotransformation

         The fate of orally administed 14C-captan was studied in eight
    male and eight female Simonsen albino rats, received from Simonsen
    Laboratories, Gilroy, USA, weighing 185-200 g. The animals were given
    100 mg/kg bw  N-trichloro-[14C]-methylthio-4-cyclohexene-1,2-
    dicarboximide (0.34 mCi/mmol, aqueous suspension in 1 ml of 1%
    traganth gum and 005% Tween-20) by gastric intubation, and radiolabel
    was determined in urine, faeces, and expired air. Within 9 h, 50% of
    the dose had been excreted; the final distribution was 52% in urine,
    23% in expired air, 16% in faeces, and 0.6% in tissues. The urinary
    metabolites were identified as thiazolidine-2-thione-4-carboxylic acid
    (19%), a salt of dithiobis(methane-sulfonic acid) (54%), and the
    disulfide monoxide derivative of dithiobis(methanesulfonic acid)

    (14%). 14C-Carbon dioxide was identified in expired air. Radioactive
    thiazolidine-2-thione-4-carboxylic acid was detected in the urine of
    rats treated simultaneously with captan and either [U-14C]cystine or
    reduced 35 S-glutathione. 35 S-Dithiobis(methanesulfonic acid) was
    excreted in the urine of rats treated simultaneously with sodium
    35 S-sulfite and either captan or thiophosgene. The metabolism of
    captan thus appears to involve evolution of thiophosgene derived from
    the trichloromethylthio moiety. Thiophosgene is detoxified, at least
    in part, by three mechanisms: (i) oxidation and/or hydrolysis to
    carbon dioxide; (ii) reaction with a cysteine moiety to yield
    thiazolidine-2-thione-4-carboxylic acid; and (iii) reaction with
    sulfite to produce dithiobis(methanesulfonic acid). Degradation in the
    gastrointestinal tract appears to play a major role in the metabolism
    of captan (DeBaun  et al., 1974).

         The metabolites of captan were measured in the urine and faeces
    of five male and five female Sprague-Dawley rats (weighing 192-260 g,
    obtained from Charles River, Margate, Kent, United Kingdom) treated
    with a single oral dose of 10 or 500 mg/kg bw [14C-cyclohexene
    ring]-labelled captan. Some of the animals that received the dose of
    ]0 mg/kg bw were pretreated with 10 mg/kg bw unlabelled captan for 14
    days. Seven urinary metabilites were identified: 3-hydroxy-4,5-
    cyclohexene-1,2-dicarboximide (42%), 5-hydroxy-3,4-cyclohexene-
    1,2-dicarboximide (6%), 6-hydroxy-1-amido-2-carboxy-4,5-cyclohexene
    (13%), 4,5-cyclohexene-1,2-dicarboximide (11%), 1-amido-2-carboxy-
    4,5-cyclohexene (7%), 4,5-dihydroxy-1,2-dicarboximide (6%), and
    4,5-epoxy-1,2-dicarboximide (5%). Two unidentified metabolites
    account:ed for 4 and 2%, respectively, of the urinary radiolabel.
    Radiolabel remaining at the origin of the thin-layer chromatography
    plates, which could not be matched to identified metabolites,
    accounted for 7% of the urinary radiolabel. No significant difference
    was noted between the sexes or between dosing regimes in the quantity
    of urinary metabolites. Faecal extracts obtained from rats dosed with
    10 and 500 mg/kg bw captan contained 7 and 43% respectively, of an
    unidentified metabolite (possibly captan). 4,5-Cyclohexene-1,2-
    dicarboximide accounted for an average of 35% of the faecal
    metabolites. 3-Hydroxy-4,5- or 5-hydroxy-3,4-cyclohexene-1,2-
    dicarboximide were major faecal metabolites, the quantities depending
    on the treatment regime and sex. 4,5-Dihydroxy-1,2-dicarboximide,
    1-amido-2-carboxy-4,5-cyclohexene, and polar metabolites were found in
    only relatively small amounts, and 4,5-epoxy-1,2-dicarboximide was not
    detected in faecal extracts (Lappin & Havell, 1990).

         The dermal and oral absorption and metabolism of captan were
    studied in a pilot study of two human volunteers, and the results were
    compared with earlier findings in rats (Krieger & Thongsinthusak,
    1993). The usefulness of thiazolidine-2-thione-4-carboxylic acid and
    4,5-cyclohexene-1,2-dicarboximide as biomarkers of occupational
    exposure was also evaluated. Both compouns were rapidly detected after
    dermal application of 15 mg captan (purity, 99.1%) dissolved in 1 ml

    chloroform (analytical reagent grade) to two healthy adult men
    weighing 84 and 150 kg. The concentration of 4,5-cyclohexene-1,2-
    dicarboximide in 12-h urine samples was 5-640 ppb (the lower limit was
    the minimal detectable limit), and the concentrations were stable for
    at least one year when the samples were stored at -20░C. Thiazolidine-
    2-thione-4-carboxylic acid was also stable, but the minimal detectable
    limit was 50 ppb. The same two individuals took oral doses of 0.1 or
    1 mg/kg bw, urine was collected at 12-h intervals for four days, and
    the samples were analysed for same two metabolites. Both were detected
    in urine within the first 24 h (Figure 1) but represented only small
    percentages of the dose of captan administered: thiazolidine-2-thione-
    4-carboxylic, 4-9%, and 4,5-cyclohexene-1,2-dicarboximide, 1-3%,
    perhaps because there are alternative metabolic pathways. In an
    earlier study in rats (DeBaun  et al., 1974) given captan at much
    higher oral doses (77-100 mg/kg bw), 4,5-cyclohexene-1,2-dicarboximide
    and thiazolidine-2-thione-4-carboxylic acid in the urine represented
    13 and 19%, respectively, of the dose of captan. In the rats,
    4,5-cyclohexene-1,2-dicarboximide was further metabolized by
    hydroxylation, epoxidation, rearrangement, and internal scission to
    products that were not assayed in the study of humans. Although the
    authors of the study in humans concluded that dermal and oral
    metabolism of captan are different in man and rats, the study did not
    demonstrate species differences. The significantly higher doses used
    in rats, the limited number of human volunteers, and the lack of
    information on other metabolites limited the conclusions that could be
    drawn.

    CHEMICAL STRUCTURE 1

    2.  Toxicological studies

    (a)  Short-term toxicity

    Mice

         Two groups of 15 male CD1 mice were fed diets containing 0 or
    6000 ppm captan (purity, 89.4%) for up to 91 consecutive days. The
    concentration of captan was within 4% of nominal concentration, and
    the homogeneity and stability of the diet were satisfactory for the
    period and conditions of storage used. The animals were observed
    daily; body weights were recorded daily for the first week of the
    study and weekly thereafter. Food consumption was recorded throughout
    the study. Five animals per group were killed after 28, 56, and 91
    days of treatment and examined  post mortem. The small intestine
    (duodenum, ileum, and jejunum) was removed and prepared by a 'gut
    rolling' procedure, starting at the ileo-caecal junction. Sections
    were stained with haematoxylin and eosin or with antibodies to
    proliferating cell nuclear antigen and examined by light microscopy.
    Sections were evaluated for histopathological change, for
    proliferating cell nuclear antigen labelling index (percent cells in
    the crypts labelled with antigen), for mean number of crypt cells, and
    for the ratio of villus to crypt height.

         Body-weight loss was seen among treated mice during the first
    week of the study in association with significantly reduced food
    consumption. This was considered to reflect the unpalatability of the
    captan diets. Food consumption was similar to that of controls from
    week 2 until the end of the study, and the body-weight gain of treated
    mice was similar to that of controls for the remainder of the study.
    The body weights, however, were significantly lower than those of
    controls from week 2 until the end of the study.

         The only macroscopic findings in treated mice killed after 28
    days was pronounced thickening of the duodenal mucosa. Similar but
    less pronounced effects were observed in treated mice killed after 56
    or 91 days. Histopathological changes in the small intestine were
    recorded at all times in treated animals. The effects consisted of
    marked crypt-cell hyperplasia with concomitant atrophy of the
    associated villi and were limited to approximately the first 7 cm of
    the duodenum. A marked increase in the number of mitotic figures was
    seen within the hyperplastic crypts. There was also increased
    inflammatory cell infiltrate in the expanded lamina propria, limited
    to the area of the duodenum with diffuse cell hyperplasia. The
    inflammatory cells were predominately mononuclear and were most
    prominent at day 28. At later times, only occasional villi were
    affected by the inflammatory cell infiltrate. In addition to the
    diffuse hyperplasia seen at day 28, focal crypt hyperplasia,

    characterized by increased crypt profiles and focal flattening of the
    villi, was present in animals killed on days 57 and 92. Again, the
    effect was confined to approximately the first 7 cm of the duodenum.

         The proliferating cell nuclear antigen labelling index was
    increased in the crypt cells in the proximal duodenum, and the average
    number of cells per duodenal crypt was increased at all times in
    treated mice. The highest crypt cell number was seen at day 28, and
    there was a trend for the number of cells to decrease with increasing
    exposure to captan, the villus to crypt height ratio was biologically
    significantly reduced in treated mice at all times. Thus, in this
    study, prominent crypt-cell hyperplasia was produced within the first
    28 days in the duodenum of mice fed a diet containing 6000 ppm captan.
    The effect was also present at 56 or 91 days but was diminished,
    probably by compensatory mechanisms (Allen, 1994).

         Groups of five male and five female CD1 mice (body weights,
    33.8-35.2 g), received as weanlings (29-33 days old) from Charles
    River, Margate, Kent, United Kingdom, were fed diets containing 0,
    400, 800, 3000, or 6000 ppm captan (purity, 89.4%) for 56 days.
    Analysis of the diets showed that the achieved dietary concentrations
    of captan were within 9% of target levels; the homogeneity (maximum
    deviation, 6.8%) and chemical stability of captan in the diet stored
    at room temperature over 24 days (87.5-100% of the initial
    concentration) or over 73 days at -20░C (85.2-109% of the initial
    concentration) were also satisfactory. Clinical signs, body weight,
    and food consumption were monitored daily for the first week and then
    weekly for the remainder of the study. At termination on day 57, the
    animals were sacrificed, and the small intestine was prepared for
    histopathology by a 'gut rolling' procedure, starting at the
    ileo-caecal junction and rolling forward to the duodenum. Duodenal
    hyperplasia was evaluated by (i) visual examination of routinely
    stained sections for histopathological changes, (ii) assessment of the
    mean number of cells in the crypt-cell population, (iii) measurement
    of the bromodeoxyuridine labelling index (percent cells labelled with
    bromodeoxyuridine as a ratio to the total number of cells in the
    crypts), and (iv) measurement of the ratio of villus to crypt height.
    The stomach, jejunum, and ileum were evaluated for histopathological
    changes only.

         The body-weight gains of mice fed 3000 or 6000 ppm were lower
    than those of controls throughout the study, and there was a slight
    reduction at 400 and 800 ppm, although this was confined to the first
    few days. A similar pattern of change was seen in food consumption and
    was consistent, at least in part, with a reduction in the palatability
    of the diet containing captan. Captan induced a morphologically
    discernible diffuse hyperplasia of the crypt cells, which was
    localized to the first 7 cm of the duodenum after the pylorus of the
    stomach, at 3000 and 6000 ppm in males and at 800, 3000, and 6000 ppm
    in females. There was an increase in the crypt-cell labelling index at

    3000 and 6000 ppm in animals of each sex and an increased incidence in
    the numbers of cells in the crypt-cell population at dietary levels of
    800 ppm and above. In addition, a decrease in the villus to crypt
    height ratio was seen at 3000 and 6000 ppm in both males and females.
    These changes were accompanied by mononuclear inflammatory cells in
    the lamina propria. Mild crypt-cell hyperplasia in the jejunum of male
    mice was seen at 3000 and 6000 ppm, and there was mild hyperplasia of
    the forestomach epithelium with hypertrophy of the gastric pits of the
    glandular portion of the stomach in males at 3000 ppm and in animals
    of each sex at 6000 ppm. The NOAEL was 400 ppm on the basis of
    pathological changes including duodenal hyperplasia (Tinston, 1995).

    Rats

         The effect of captan on preneoplastic enzyme-altered liver foci
    was studied in groups of 15 male Fischer 344 rats, six weeks old,
    given 200 mg/kg bw  N-nitrosodiethylamine intraperitoneally and two
    weeks later fed 4000 ppm (equivalent to 200 mg/kg bw) captan (purity,
    90.5%) for six weeks and then sacrificed. The rats underwent a partial
    hepatectomy at week 3. A small increase in the number of glutathione
     S-transferase (placental form)positive foci was seen, but the effect
    was reported to be borderline. There was no effect on mortality or
    body-weight gain (Cabral  et al., 1991).

    (b)  Genotoxicity

         The potential for captan to interact with DNA was studied
     in vivo in Swiss ICR-derived CD-1 mice and Osborne-Mendel rats which
    received a suspension of 14C-trichlormethyl-captan (radiochemical
    purity, 96-98%; specific activity, 19 mCi/mmol) by gavage. DNA was
    isolated from various tissues and radiolabel was assayed by
    scintillation spectrometry. Male mice receiving 1600 mg/kg bw and male
    and female rats given 300 mg/kg bw of labelled captan were sacrificed
    4 or 24 h after treatment, and DNA was extracted from the liver and
    testis. No significant disintegration was found to be associated with
    the DNA from either organ. Rats were not used in subsequent
    experiments because the amount of radiolabelled material with high
    specific activity was not sufficient to treat both mice and rats.

         Radiolabel was associated with DNA in all of the organs from mice
    that were examined (stomach, duodenum, intestine, kidney, liver,
    testis) 24 h after oral administration of 156 mg/kg bw labelled captan
    (50-56 mCi/mmol). No correlation was seen between the level of
    captan-DNA associations and the site of tumour formation. Since
    information on the spectrum and structure of the captan-induced DNA
    modifications in specific tissues after administration of captan was
    not available, the authors were not able to correlate the observed
    associations with proposed mechanisms of carcinogenesis. Dialysis used
    to investigate the nature of the captan-DNA interactions  in vivo
    indicated that up to 90% of the detected radioactivity represented

    either non-covalently associated captan or covalent associations that
    were hydrolysed non-enzymatically, releasing soluble, labelled
    nucleotides. The exact nature of the remaining captan-DNA associations
    was not known (Selsky & Matheson, 1981).

         The effect of captan on microtubules and micro filaments was
    studied  in vitro in tubulin prepared from porcine brain and in
    cultured mouse fibroblasts. Turbidometry at 350 nm showed that captan
    caused a dose-dependent inhibition of tubulin assembly after
    incubation. At equimolar concentration with tubulin (30 Ámol/litre),
    captan totally inhibited microtubule formation; at lower
    concentrations (5-30 Ámol/litre), captan also promoted disassembly of
    preformed microtubules. These effects were confirmed by electron
    microscopy. Immunofluorescent microscopy of cultured mouse fibroblasts
    showed that captan also depolymerized microtubules, and the extent of
    microtubule disassembly was concentration- and time-dependent. While a
    3-h incubation of the cells with 10 mmol/litre captan was required to
    completely disturb the microtubular structures, a 12-h incubation with
    5 Ámol/litre was required to produce the same effect. Recovery of
    microtubules was observed when preincubated cells were washed
    extensively. The effect of captan on microtubules was considered to be
    specific, since in equimolar concentrations  in vitro it did not
    interact with G-or F-actin isolated from rabbit muscle or with the
    fluorescent actin pattern in mouse fibroblasts incubated with
    10 mmol/litre captan for up to 12 h. Microfilaments typical of
    untreated cells were seen in captan-treated fibroblasts. Thus, captan
    interacts at equimolar concentrations with tubulin, affecting the
    assembly and disassembly of microtubules in isolated tubulin and
    cultured mammalian cells (Stournaras  et al., 1991).

         Groups of 100 male CD-1 mice were given a single dose of
    890 mg/kg bw of 35 S-captan (radiochemical purity, 95%; specific
    activity, 888 MBq/mmol per litre), 82 mg/kg bw of 14C-1-methyl-1-
    nitrosourea (positive control), or a vehicle formulation by gavage.
    Six hours after sacrifice, the stomach, jejunum, liver, and bone
    marrow were sampled, and DNA was extracted from each tissue and
    purified; the radiolabel associated with these DNA extracts was then
    measured. Radiolabel was shown to be associated with DNA extracts
    originating from all tissues of mice treated with captan or the
    positive control but not from those given the vehicle. Covalent
    binding indexes (micromoles of captan bound per mole of nucleotide
    divided by millimoles of captan administered per kilogram body weight)
    of 2.8, 38, 38, 46, and 91 were determined for DNA from bone marrow,
    liver, stomach, dudenum, and jejunum, respectively. Selected tissues
    were further purified in order to determine whether the radiolabel in
    the extracts was associated with DNA. Radiolabel in liver extracts
    from captan-treated mice, but not from positive control mice, was
    found at the base of the tube, away from the main DNA fraction. In
    contrast, radiolabel associated with DNA from the jejunum and duodenum
    of captan-treated animals clearly separated at a higher position on

    the density gradient than the main DNA fraction. Although captan was
    associated with DNA in all of the organs examined, this study did not
    indicate whether the association was covalent (Pritchard & Lappin,
    1991).

         When 14C-captan (radiochemical purity, 95-98%) was incubated at
    25░C with calf thymus DNA, about 0.3% of the radiolabel was associated
    with the DNA. In the absence of glutathione, this association was
    present at time zero and did not increase with time, suggesting that
    the radiolabel represents loosely bound, unextracted material rather
    than covalently bound adducts. In the presence of glutathione, the
    amount of radiolabel associated with DNA appeared to increase
    initially but rapidly reached a constant level, which again was
    independent of time. In both cases, the level of associated radiolabel
    was dependent on the concentration of captan but was unaffected by pH.
    Because of the high levels of associated radiolabel at time zero, the
    lack of effect of time and pH, and the low radiochemical purity of the
    captan used, it could not be concluded that captan binds to DNA to any
    significant extent under these conditions. These results also preclude
    identification of the DNA adducts. After incubation of 14C-captan
    with each deoxynucleoside or DNA base in the presence or absence of
    glutathione, no reaction was seen with captan, as measured by
    high-performance liquid chromatography and scintillation counting of
    the eluent.

         Groups of 6-12 male CD-1 mice weighing 30-40 g (6-8 weeks old)
    were each given a single dose of 3 mmol/kg bw 35 S-N-acetylcysteine,
    2-oxo-[35 S]-thiazolidine-4-carboxylate, 2-thioxo-[35 S]-
    thiazolidine-4-carboxylate, or 35 S-captan in vehicle by gavage;
    another group of male mice was given the vehicle alone. Six hours
    after treatment, the mice were killed, their livers were removed and
    homogenized, and DNA extracts were examined. The study indicated no
    significant covalent binding of captan to DNA, despite the very large
    doses administered.

         These studies provide no clear evidence for a reaction between
    captan or its breakdown products and DNA bases or deoxynucleosides.
    Furthermore, captan is, at best, an extremely weak genotoxin
     in vivo. Any binding of captan to DNA must be extremely low and
    would be impossible to measure by currently available methods. Thus,
    the tumours seen in mice must arise by a mechanism other than one
    involving direct interaction between captan and DNA (Provan  et al.,
    1992).

         The genotoxicity of captan was also studied  in vitro in
    cultured human foreskin fibroblasts. Treatment with 0.16- 1.7
    Ámol/litre captan reduced cloning ability and produced DNA
    single-strand breaks and DNA-protein cross-links; an excision repair
    response was elicited at 17-260 Ámol/litre. Captan also inhibited
    cellular DNA synthesis at 3-17 Ámol/litre and formed stable adducts in

    herring sperm DNA and human cellular DNA. Misincorporation of
    nucleotides into synthetic DNA templates was significantly increased
    after treatment with captan at 1-12 mmol/litre  in vitro in the
    presence of  Escherichia coli DNA polymerase I, suggesting that DNA
    adduct formation with captan could have mutagenic consequences. This
    study shows that captan can interact with DNA at a number of levels
    and that these interactions may provide the basis for a genotoxic
    effect. The extreme cytotoxicity of the compound could, however, be
    due to other cellular effects, since at the IC50 for cell killing
    (about 0.8 Ámol/litre), none of the genotoxic events was seen (Snyder,
    1992).

    Comments

         The excretion profiles of male and female rats were similar, the
    urinary route predominating. The residual tissue concentrations seven
    days after dosing were negligible in animals of each sex, the highest
    concentrations being found in the kidneys and blood. The metabolism of
    captan in rats appears to involve the evolution of thiophosgene,
    derived from the trichloromethylthio moiety. Thiophosgene is
    detoxified, at least in part, by three mechanisms: oxidation and/or
    hydrolysis to carbon dioxide; reaction with the cysteine moiety of
    glutathione to yield thiazolidine-2-thione-4-carboxylic acid; and
    reaction with sulfite to produce dithiobis(methanesulfonic acid).
    Degradation in the gastrointestinal tract appears to play a major role
    in the metabolism of captan.

         Studies on the hyperplasia induced by captan showed prominent
    crypt-cell hyperplasia within 28 days in the proximal duodenum of mice
    fed diets containing 6000 ppm captan for 91 days or 800, 3000, or
    6000 ppm for 56 days. The NOAEL was 400 ppm, the lowest dose
    administered for 56 days, equivalent to 60 mg/kg bw per day, on the
    basis of duodenal hyperplasia.

         Captan has been adequately tested for genotoxicity in a range of
    assays, which demonstrate that it is mutagenic and clastogenic
     in vitro but not  in vivo. The in-vitro responses are reduced or
    abolished by the presence of liver homogenates, serum, glutathione, or
    cysteine whenever these experimental modifications have been
    investigated. Studies of the genotoxicity of captan in mouse duodenum
    indicate that it does not bind covalently to DNA (although metabolic
    incorporation of the  N-trichloromethylthio-carbon does occur) and
    nuclear aberrations are not induced. The Meeting concluded that captan
    does not present a significant genotoxic risk, owing to the presence
    of an efficient detoxification mechanism  in vivo.

         There appear to have been no studies on the effects of captan on
    glutathione levels analogous to those conducted with folpet. Dietary
    studies of 4-8 weeks' duration have shown that irritation and
    consequent inflammation as well as hyperplasia occur in the proximal
    duodenum of mice. These data indicate that sustained proliferative
    stimulation of the proximal duodenum is a consequence of oral
    administration of captan. The Meeting concluded that this finding
    represents an important element in the process by which captan,
    which is not genotoxic  in vivo, induces tumours in the mouse
    gastrointestinal tract.

         The information available to the present Meeting provides no
    basis for altering the existing ADI for captan, which is based on an
    NOAEL of 12.5 mg/kg bw per day determined in studies of reproductive
    toxicity in rats and monkeys, and a 100-fold safety factor.

    Toxicological evaluation

     Levels that cause no toxic effect

    Mouse:    400 ppm equivalent to 60 mg/kg bw per day (56-day study of
              toxicity)

    Rat:      250 ppm, equivalent to 12.5 mg/kg bw per day (study of
              reproductive toxicity)

    Dog:      100 mg/kg bw per day (66-week study of toxicity)

    Monkey:   12.5 mg/kg bw per day (study of developmental toxicity)

     Estimate of acceptable daily intake for humans

         0-0.1 mg/kg bw

     Studies that would provide information useful for continued
     evaluation of the compound

         Further observations in humans

    References

    Allen, S.L. (1994) Captan: Investigation of duodenal hyperplasia in
         mice. Unpublished report No. CTL/L/5674 from Zeneca Central
         Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire,
         United Kingdom. Submitted to WHO by Zeneca Agrochemicals,
         Fenhurst, Haslemere, Surrey, United Kingdom.

    Bratt, H. (1990) Captan: Repeat dose study (10 mg/kg) in the rat.
         Unpublished report No. CTL/P/2958 from ICI Central Toxicology
         Laboratory, Alderley Park, Macclesfield, Cheshire, United
         Kingdom. Submitted to WHO by ICI Agrochemicals, Fernhurst,
         Haslemere, Surrey, United Kingdom.

    Cabral, R, Hoshiya, T., Hakol, K., Hasegawa, R. Fukushima, S. & Ito,
         N. (1991) A rapid in vivo bioassay for the carcinogenicity of
         pesticides.  Tumori, 77, 185-188.

    DeBaun, J.R., Miaullis, J.B., Knarr, J. Mihailovski, A. & Menn, J.J.
         (1974) The fate of  N-trichloro[14C]-methylthio-4-cyclohexene-
         1,2-dicarboximide ([14C]captan) in the rat.  Xenobiotica, 4,
         101-119.

    Krieger, R.I. & Thongsinthusak, T. (1993) Captan metabolism in humans
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    See Also:
       Toxicological Abbreviations
       Captan (HSG 50, 1990)
       Captan (ICSC)
       Captan (PIM 098)
       Captan (FAO/PL:1969/M/17/1)
       Captan (WHO Pesticide Residues Series 3)
       Captan (WHO Pesticide Residues Series 4)
       Captan (Pesticide residues in food: 1977 evaluations)
       Captan (Pesticide residues in food: 1978 evaluations)
       Captan (Pesticide residues in food: 1980 evaluations)
       Captan (Pesticide residues in food: 1982 evaluations)
       Captan (Pesticide residues in food: 1984 evaluations)
       Captan (Pesticide residues in food: 1984 evaluations)
       Captan (Pesticide residues in food: 1990 evaluations Toxicology)
       Captan (IARC Summary & Evaluation, Volume 30, 1983)