IPCS INCHEM Home


    FAO/PL:1969/M/17/1

    WHO/FOOD ADD./70.38

    1969 EVALUATIONS OF SOME PESTICIDE RESIDUES IN FOOD

    THE MONOGRAPHS

    Issued jointly by FAO and WHO

    The content of this document is the result of the deliberations of the
    Joint Meeting of the FAO Working Party of Experts and the WHO Expert
    Group on Pesticide Residues, which met in Rome, 8 - 15 December 1969.

    FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS

    WORLD HEALTH ORGANIZATION

    Rome, 1970

    CAPTAFOL

    IDENTITY

    Chemical name

    N-(1,1,2,2-tetrachloroethylthio)-3a,4,7,7a-tetrahydrophthalimide

    N-(1,1,2,2-tetrachloroethylthio)cyclohex-4-ene-1,2-dicarboximide

    N-(1,1,2,2-tetrachloroethylmercapto)-4-cyclohexene-1,2-dicarboximide

    N-(1,1,2,2-tetrachloroethylsulphenyl)-cis-delta-
    4-cyclohexene-1,2-diocarboximide

    N-(1,1,2,2-tetrachloroethyl) thiotetrahydrophthalamide

    Synonyms

    Difolatan(R)

    Structural formula

    CHEMICAL STRUCTURE 

    Other relevant chemical properties

    The pure material is a white crystalline solid; m.p. 160 to 161C. It
    is practically insoluble in water (less than 1 ppm) and slightly
    soluble in most organic solvents. The technical material is a
    recrystallized product of 98 percent purity; the impurities consist of
    0.5-1.5 percent toluene, 0.5-1.5 percent tetrahydrophthalimide (THPI),
    and 0.1-0.2 percent unknown chlorinated substances. It is a light tan
    powder with a characteristic odour. It is formulated as 80 percent
    wettable powder (Ortho Difolatan 80 W) and as flowable water
    suspension (4 lbs per U.S. gallon). Captafol is stable except under
    alkaline conditions.

    EVALUATION FOR ACCEPTABLE DAILY INTAKE

    BIOCHEMICAL ASPECTS

    Captafol (1), on hydrolysis, yields tetrahydrophthalimide (II),
    chloride ion, dichloroacetic acid (III) and inorganic sulphur in
    various oxidation states. In the presence of sulfhydryl compounds at
    neutral or slightly alkaline pH, captafol is rapidly degraded to
    tetrahydrophthalimide and chloride ion and no organochlorine compound
    is formed. This reaction with sulfhydryl compounds is much faster than
    the hydrolytic reaction and it may be the dominant reaction in a
    biological system where sulfhydryl groups are present. It is also well
    known that the -N-S- bond in organic compounds is easily subject to
    certain types of chemical attack, and two mechanisms for the cleavage

    of this bond in captafol have been proposed; either nucleophilic
    attack by a sulfhydryl compound or the slower hydrolytic reaction
    (Kohn, 1965; Berteau et al., 1966). 

    CHEMICAL STRUCTURE 

    Shay rats were fed captafol at levels of 60 and 600 ppm in the diet.
    At several intervals the stomach contents were analysed. Captafol
    degraded rapidly, the reaction having a half-life of about three
    hours. Both tetrahydrophthalimide and tetrahydrophthalic acid were
    detected. No dichloroacetic acid was detected at the low dose level
    but small amounts of it were found at the 600 ppm level, the maximum,
    found 0.5 hours after feeding, being about 1 percent of the original
    dose given (Leary, 1966).

    Rats, dogs and monkeys were fed carbon14-carbonyl-labelled captafol
    and radioactivity measurements were performed on expired carbon
    dioxide, faeces. urine and various tissues. Almost 80 percent of the
    dose given was excreted within 36 hours, mainly via the urine with
    smaller amounts in the faeces and none in the expired carbon dioxide.
    Less than 0.5 percent of the dose remained in the liver, heart,
    kidneys, blood, muscle or fat. The rate of excretion of carbon14 was
    almost identical for all three species. Unchanged captafol accounted
    for the majority of the radioactivity in the faeces, but no captafol
    was detected in blood, tissues or urine. The primary metabolite,
    tetralydrophthalimide was detected in blood, faeces and urine although
    the major portion of the activity in blood and urine was due to other,
    more water-soluble metabolites. The epoxide of captafol was not
    detected in blood, urine or faeces and it was concluded the
    epoxidation is not a metabolic route (Dye, 1969).

    Captafol differs from captan only in the nature of the halogenated
    group attached to the sulphur. Both compounds give the same
    decomposition product tetrahydrophthalimide. Therefore, all the
    information on the metabolism of captan relative to the imide portion
    of the molecule is considered to be applicable to captafol (Dye,
    1969). (See the monograph on captan).

    Special studies on reproduction

    Rat

    Groups of 8 male and 16 female rats were fed captafol at 0, 50 (raised
    to 100 after first generation), 250 (raised to 500 after first
    generation), and 1000 ppm in the diet in a three-generation
    reproduction study. There were no adverse effects on body-weight gain,
    mortality, or organ-weights of parental animals or on reproductive
    performance, fertility and lactation indices, litter-size, or number
    of stillbirths in any test group. Pup survival in the test groups at
    various intervals in the lactation period was not significantly
    different from the control group. Weanling body-weights in the 1000
    ppm group were depressed in both males and females in the first and
    third generations. Weanlings of the second generation showed only
    slight weight depression. This effect on weanling weights did not
    occur at the lower test levels (even after they were raised to 100 and
    500 ppm). Gross examinations and histopathology carried out on
    parental animals and on weanlings in the 0 and 1000 ppm groups
    revealed no changes that could be attributed to captafol (Kennedy et
    al. 1966).

    Special studies on teratogenicity

    Chicken-egg

    Captafol was injected, in dimethylsulfoxide solution, into either the
    yolk or air cell of fresh fertile eggs at levels from 3-20 mg/kg
    egg-weight. The eggs were incubated and non-viable embryos and hatched
    chicks were examined for gross abnormalities. In a total of 270 eggs
    treated with captafol, the incidence of malformations was 6.67 percent
    compared to the control value of 1.6 percent for 1500 eggs injected
    with dimethylsulfoxide alone. In the same experiment the metabolite
    tetrahydrophthalimide was also injected. Of 1025 eggs the incidence of
    malformation was 4.78 percent. The epoxy-derivative of captafol
    ("captafol-epoxide") was also tested for its effect on chicken eggs.
    Of 115 eggs into which this compound was injected. the incidence of
    malformation was 15.05 percent. In all cases the malformations
    consisted mainly of micromelia, amelia and phocomelia (Verrett et al.,
    1969).

    Monkey

    Groups of seven pregnant Rhesus monkeys were given oral doses of 6.25,
    12.5 or 25 mg of technical captafol per kg of body-weight from
    gestation day 22 through 32. Another group of seven pregnant females
    received 10 mg/kg body-weight of thalidomide, on days 25, 26 and 27.
    Three additional females ware treated with 15 consecutive doses of
    captafol at 12.5 mg/kg body-weight later in gestation (66-80, 81-959
    and 86-100 days). All doses were administered by gastric intubation of
    a suspension in 0.9 percent gelatin solution in the morning before
    feeding. All the females used had produced at least one live, normal
    baby prior to this study. Pregnancies were terminated by Caesarean
    section at approximately the 84th day of gestation. The three monkeys
    receiving captafol later in gestation were allowed to proceed to term
    and deliver their young unaided. Careful examination of 19 foetuses
    from the captafol-treated monkeys, including gross observation, X-ray
    and skeletal examination following alizarin red S staining, revealed
    no abnormalities. Internal structural formation, observed both grossly
    and by evaluation of organ-weight and organ to body-weight ratio data,
    was normal. Foetal mortality (resorption or abortion) occurred in the
    sixth week of pregnancy in two of the seven animals receiving 25 mg/kg
    of captafol. In the group given thalidomide teratogenic activity (limb
    malformations) was observed in five of the seven foetuses. The three
    monkeys allowed to proceed to term delivered three normal babies, as
    indicated by external and X-ray examination (Kennedy et al., 1968b).

    Rabbit

    Groups of 10 pregnant Dutch Belted rabbits received daily oral doses
    of 0 or 75 mg/kg body-weight of technical captafol. A third group was
    given thalidomide at 75 mg/kg body-weight. Dosing, administered by
    gelatin capsule, began on day 6 and ended on day 16 of the gestation
    period (the day of conception being day 0). On day 28, each doe was
    sacrificed and the foetuses removed by Caesarean section. The rabbits
    given captafol lost weight over the period of treatment. One doe in
    this group aborted eight young, another showed one resorption site.
    Three does in the thalidomide group showed evidence of resorption. Of
    the viable young, 86 percent from the group given captafol survived a
    six hour incubation (37C) period compared with 100 percent in the
    control group. No abnormalities were seen among 74 young in the group
    given captafol. Animals in the group given thalidomide showed
    significant teratogenic effects (Ives and Calandra, 1965; Kennedy et
    al., 1968a).

    Groups of 10 pregnant New Zealand albino rabbits were given technical
    captafol (98.9 percent purity) at doses of 0, 37.5, 75, 112.5 or 150
    mg/kg body-weight on gestation day 6 through 18 inclusive. A positive
    control group was given 75 mg/kg body-weight of thalidomide. All doses
    were administered via gelatin capsule. On day 29 each doe was
    sacrificed and the young were removed by Caesarean section, weighed

    and observed for abnormalities. At the lowest level tested, there was
    no maternal mortality and the animals gained weight, although not as
    much as the controls. Resorption sites occurred in 2 of the 10 females
    (three sites). Examination of 62 foetuses from this group revealed no
    abnormalities. Body-weights and 24-hour incubator survival were
    comparable to those of the control group. At all the higher
    dose-levels, toxic effects were seen in the mothers. Deaths occurred
    in each group and resorption sites were prevalent in the survivors.
    However, all young delivered in all three groups were free of gross
    teratologic effects and survived the 24-hour incubation period.
    Body-weights were lower than those of controls. In the group given
    thalidomide, 32 of 55 foetuses showed abnormalities (Jackson at al.,
    1967; Kennedy et al., 1968a).

    Rat

    A group of nine pregnant female rats was given doses of 100 mg/kg
    body-weight/day of captafol orally from day 6 to day 15 of gestation
    and another group of five pregnant rats was given 500 mg/kg from day 8
    to day 10. Examination of 180 foetuses revealed no gross malformations
    (Kennedy et al., 1968a).

    Special studies on the metabolite, tetrahydrophthalimide

    Rabbit (teratogenic study)

    Groups of 10 female Dutch Belted rabbits received 0 or 75 mg/kg
    body-weight of tetrahydrophthalimide, the hydrolytic metabolite of
    captafol, from day 6 to 16 inclusive of the gestation period. A
    treated control group was given 75 mg/kg bodyweight of thalidomide
    over the same period. The doses were given orally via gelatin capsule.
    On day 28 each doe was sacrificed, the young were removed by Caesarean
    section and examined for abnormalities. Examination of 57 embryos from
    the test group revealed no external or skeletal abnormalities.
    Fourteen embryos of a total of 44 in the group given thalidomide had
    skeletal abnormalities. There was an increase in the occurrence of
    resorption sites in the test group compared with the controls. Five of
    the ten females exhibited one to three resorption sites (a total of
    nine) although the number of viable young in the group was not reduced
    (Palazzolo at al., 1966; Kennedy at al., 1968a).

    Acute toxicity

                                                                      
                              LD50
    Animal    Route     mg/kg body-weight          References
                                                                      

    Rat       oral            62001/         Palazzolo et al., 1965a

    Rat       oral            50002/         Palazzolo et al., 1965b

    (continued)
                                                                      
                              LD50
    Animal    Route     mg/kg body-weight          References
                                                                      

    Rat       oral            25002/         Palazzolo et al., 1964

    Rabbit    dermal          154002/        Palazzolo et al., 1964
                                                                      

    1/ Corn oil solution
    2/ Aqueous suspension

    Short-term studies

    Dog

    Groups of two male and two female dogs were given daily doses of 0,
    10, 30, 100 or 300 mg/kg body-weight of captafol over a two year
    period. The material was given in gelatin capsules immediately after
    each day's feeding. At the two highest dose levels there was a
    decreased body-weight gain over the period of the experiment. Emesis
    and loose stools occurred quite frequently in both these groups during
    the first four weeks but only occasionally thereafter. These effects
    were not seen at the two lower levels. Increased absolute liver and
    kidney-weights and liver and kidney to bodyweight ratios were seen in
    all animals at the 30, 100 and 300 mg/kg levels. Alterations In other
    organ-weights appeared unrelated to the administration of the test
    material. Haematologic studies revealed a mild anaemia at the
    termination of the study in the dogs given 100 and 300 mg/kg per day.
    Histopathology, blood chemistry, urinalysis and liver-function tests
    revealed no adverse effects that could be attributed to the
    administration of captafol. The 10 mg/kg dose level appeared to cause
    no significant effects (Cervenka at al., 1964).

    Rabbit

    Four groups of eight rabbits were given dermal applications of
    captafol at levels of 0, 500, 1000 and 2000 mg/kg body-weight/day for
    20 days. Half the animals in each group were treated on abraded skin
    areas, the other half on intact skin. There was a marked adverse
    effect on body-weight, even at the lowest level tested. Deaths
    occurred at all test levels and the 20-day dermal LD50 was found to
    be 1100 mg/kg body-weight/day (for the 80 percent wettable powder).
    The only effects seen in gross and microscopic examinations were in
    the skin at the application site (Palazzolo et al., 1964).

    Long-term studies

    Rat

    In a two year study with captafol added to the diet at 0 (70 males and
    70 females), 250, 500, 1500 and 5000 ppm (35 females and 35 males at
    each test level), there was growth depression at the 1500 and 5000 ppm
    levels. Mortality was increased in the 5000 ppm group, with no males
    left alive after 23 months. A lymphocyte to neutrophile shift was
    observed in the surviving males of this group after 21 months. There
    was an increase in the liver to body-weight ratio at the 500, 1500 and
    5000 ppm levels at 12 months. An increase in this ratio was also seen
    in males at 250 ppm. At the end of the experiment there was no longer
    a significant difference at the two lower tent levels. Significant
    increases were also observed in organ weight and organ to bodyweight
    ratios for kidney and adrenal of rats fed at 1500 and 5000 ppm.
    Histopathology revealed liver changes characterized by degeneration of
    hepatic cells, vacuolization, incipient fat alteration, and
    infiltration by mononuclear cells. Kidney changes were characterized
    by alterations in proximal and distal tubular cells; many giant forms
    with large irregular nuclei being present. These changes in liver and
    kidney were only seen in rate fed the two highest dose levels. No
    other histopathological changes were associated with the
    administration of captafol. No effects on tumour incidence were
    observed (Kohn et al., 1964).

    COMMENT

    Captafol appears to be metabolized rapidly and in a similar way in
    rats, dogs and monkeys. The primary metabolite and other metabolites
    have been identified in excretion studies. Information is, however,
    incomplete on the nature of the metabolites in animal tissues, as well
    as on the absorption and distribution of captafol and its metabolites
    after oral administration. A two-year study in dogs indicated that a
    dose level of 10 mg/kg body-weight/day was without significant adverse
    effect. In the long-term study in rate at the lowest level tested (250
    ppm), an increase in the liver to body-weight ratio was evident at 12
    months but not at 24 months. For this reason a definite no-effect
    level has not been established in that species. Teratogenicity studies
    in mammalian species produced evidence of embryotoxic effects at the
    lowest level tested but there was no indication of malformation of the
    foetuses. The nature of the reported histopathological effects upon
    the kidney and liver observed in the two year study in rats fed high
    dose levels of captafol is of some concern.

    TOXICOLOGICAL EVALUATION

    Level causing no significant toxicological effect

    Dog: 10 mg/kg body-weight/day

    Estimate of temporary acceptable daily intake for man

    0-0.05 mg/kg body-weight/day

    RESIDUES IN FOOD AND THEIR EVALUATION

    USE PATTERN

    Pre-harvest treatments

    Captafol is used to control fungus diseases.

    Rates of application and recommended intervals between treatment and
    harvest are (Dye, 1969):

    Fruits              -    0.05 to 0.2% a.i., applied at bloom, petal
                             fall, shuck split and 10 to 14 day intervals
                             up to harvest.

    Melons              -    1.3 to 2.7 kg a.i./ha applied as needed at 7
                             day intervals up to harvest.

    Tomatoes and
    cucumbers           -    1.1. to 2.7 kg a.i./ha applied as needed at 7
                             to 10 day intervals up to harvest.

    Potatoes            -    0.10 to 1.8 kg a.i./ha applied as needed at 7
                             to 10 day intervals up to harvest.

    Post-harvest treatments

    Captafol is recommended for post-harvest use on peaches, cherries,
    plums, and nectarines (Ogawa at al., 1964).

    Other uses

    In-furrow spray application is recommended for the control of seedling
    diseases on cotton. Captafol has been used to control
    Helminthosporium heveae in rubber (Turner, 1969).

    RESIDUES RESULTING FROM SUPERVISED TRIALS

    The residue data of captafol are from treatments made under commercial
    conditions in the U.S.A. (Dye, 1969). The tests made with peaches and
    watermelons indicate that the captafol is present as a surface residue
    and is not systemically translocated into the flesh of the fruit. The
    initial residue of captafol is reduced by one half generally within a
    week or two. Two types of applications are recommended: dormant and
    blossom, and seasonal foliar. The residue data are given separately
    (Table I).

        TABLE I
                                                                                   

    Residue data from field trials

    Crop              Rate of          Number of      Pre-harvest    Captafol
                    application        treatments       interval     residue
                  (kg a.i. per ha)                       (days)       (ppm)
                                                                                   

                  Blossom application

    Apricots      3.4-8.1              3              102            0.1-0.2

    Cherries,
    sweet         2.3-10.8             2-3            45-68          0.6-1.4

    Plums         (0.1-0.3% a.i.)      2-3            131-141        n.d.-0.2

                  Seasonal foliar application

    Cherries,
    sour          1.8-3.6              4              20             7-9

    Peaches       3.1-4.5              1-13           10-14          2.5-14

    Melons        2.0-4.0              5-9            1              0.4-1.8

    Cucumbers     1.3-1.8              6-9            1              0.1-0.4

    Tomatoes      2.7-5.4              6-11           1              0.4-3.8
                                                                                   
    
    FATE OF RESIDUES

    General comments

    As outlined under 'BIOCHEMICAL ASPECTS', the N-S bond in substances
    like captafol, is subject to chemical attack. For captafol, the two
    mechanisms proposed (Kohn, 1965) are: (1) nucleophilic attack by
    sulfhydryl compounds (Anon., 1965a) acid (2) hydrolysis (Berteau,
    1963, and Potter, 1964) (Fig. 1). Both initiative reactions result in
    THPI. In addition, in reaction (1) free Cl- ions, inorganic sulphur
    compounds, and 2C-fragment are released and in reaction (2) chlorine
    is only partly appearing as free ion, the rest being bound to the
    2C-moiety. Subsequently, tetrahydrophthalimide decomposes via the
    unstable tetrahydrophthalamic acid into tetrahydrophthalic acid.

    In the presence of sulfhydryl compounds and at or near neutral pH, the
    sulfhydryl reaction (1) is much faster than the hydrolysis (2). At pH
    7 and 25C, the "half-life" of captafol in a homogeneous sulfhydryl
    reaction was found to be 4 minutes and in the corresponding hydrolysis
    1000 minutes (Anon., 1965a). As the temperature and/or pH rises the
    rates of both reactions increases.

    In animals

    The main routes of degradation of captafol in animals are the same as
    in plants (Dye, 1969).

    In plants

    Due to the extremely low water solubility of captafol the residues of
    the parent compound are occurring on the surface of the treated
    plants. This is greatly limiting the exposure of captafol to the
    degradation reaction by the sulfhydryl compounds of the plant tissue.
    As a result, the captafol residues show a high persistence in situ.

    In vitro studies on the degradation of captafol by spinach, tomato,
    and celery macerates and filtrates (Potter, 1965) have confirmed that
    captafol is very readily decomposed by the cell sap of various plants.
    There were distinct differences in the degradation rates of various
    plants. In spinach the captafol residue (10 ppm) was nearly completely
    degraded in one hour, but in tomato in about 24 hours. Boiling did not
    alter the degradative capacity of the macerates which indicates that
    no essential enzymatic reactions are involved in the degradation of
    captafol.

    The in situ residues of captafol are found to produce minor amounts
    of tetrahydrophthalimide and tetrahydrophthalic acid (Table II). No
    dichloroacetic acid has been found. Thus, even though dichloroacetic
    acid can be formed from captafol under certain conditions, it is not
    found to be present as a residue on crops treated under field
    conditions and would, therefore, not be consumed by man (Dye, 1969).

    In soils

    It has been found that captafol degrades rapidly in soil, the rate
    being a function of both the soil type and the initial concentration;
    even the longest "half-life" found was only 11 days (Berteau and Pack,
    1966a). These studies show that under normal agricultural conditions,
    the captafol that is supplied one year, even late in the season, would
    be completely degraded by the beginning of the next growing season.
    Therefore, there would be no accumulation of captafol in soil from
    year to year.

    It has been found that in natural, non-sterile soil, captafol
    degradation results in only a barely detectable trace of
    dichloroacetic acid being formed at short (i.e. one week) intervals.
    At longer intervals, none is detectable at a limit of detectability of

    0.02 ppm dichloroacetic acid itself is rapidly degraded by natural
    soil, being completely degraded within one week. In normal
    agricultural practice, therefore, there would be no buildup in the
    soil (Berteau and Pack, 1966b).

    In sterile soil, the degradation of captafol is associated with a
    buildup of dichloroacetic acid and in dichloroacetic acid fortified
    soil no loss was observed over a period of one week. The degradation
    of the acid in soil is, therefore, definitely biochemical (Berteau and
    Pack, 1966b).

    The movement of captafol through soil columns by water leaching has
    been studied. The results show that captafol does not move
    significantly and will not accumulate in water leaching from treated
    areas (Berteau and Pack, 1966c).

    Carrots and radishes were grown in soils treated with captafol to
    determine if any captafol would be taken up by the crop. At a limit of
    detectability of 0.05 ppm or better, no captafol residue was found in
    either crop (Anon., 1965a).

    In storage and processing

    All the data available indicate that the captafol residues on fruit
    are very stable under commercial storage conditions.

    In the studies on dried peaches and prunes, no residues were found in
    the fresh fruit, but small residues ware detected in the dried
    samples. Apparently, any residue in the fresh fruit was below the
    limit of detectability but this residue became detectable as it was
    concentrated in the drying operation (Table III) (Dye, 1969).

    In the canned peach samples, there was a slight residue of captafol
    detected at 1 day interval, but no detectable quantities at subsequent
    intervals. The residue of 1.6 ppm of tetrahydrophthalimide in the 1
    day peach sample decreased to below the limit of detection at 22 and
    150 days. Tetrahydrophthalic acid was barely detectable in canned
    peaches, and no detectable residues of dichloroacetic acid were found
    in any of the samples studied (Table III) (Dye, 1969).

    In the case of tomatoes no detectable residues of tetrahydrophthalic
    acid or dichloroacetic acid could be found in any of the canned fruit
    samples (Table III) (Dye, 1969).

    Because of the nature of the captafol residues they would be readily
    removed by washing, blanching, and peeling the fruit. A detailed
    evaluation can not be made because of lack of complete information.

    According to Chalkov and Vanev (1968), captafol has a suppressing
    action on wine yeast. Cabral and Tomaz (1956) reported that it
    completely inhibited fermentation of the must from treated grapes.

    METHODS OF RESIDUE ANALYSIS

    Two methods are reported to be available for the analysis of captafol
    residues in plant and animal tissues. The preferred method is electron
    capture GLC, the alternate procedure is based on thin-layer
    chromatography.

    The crop is extracted with benzene. The extract is cleaned-up by
    either a column chromatographic method or a thin layer chromatographic
    (TLC) method, or a combination of the two. The cleaned-up extract is
    then chromatographed by TLC with captafol standards. The plate is
    sprayed with N,N-dimethyl-p-phenylenediamine to visualize the spots.
    The amount of captafol is determined by visual commission of the
    sample spot with the standard spots. The method is a positive
    identification of captafol residues. Its sensitivity is about
    0.03-0.05 ppm, depending on the crop interferences (Anon., 1966b).
    There is a modified column cleanup method which is useful for oily
    crops where interferences in the thin-layer chromatography is
    encountered from plant extractives (Anon., 1964). Pomerantz and Rose
    (1968) have developed a TLC method which differentiates between
    captan, folpet, captafol, and their metabolites.

    The preferred method employs electron capture GLC for the final
    detection and estimation of residues of captafol. Either the column or
    TLC cleanup procedure can be used when cleanup is needed (Anon.,
    1965b). Twenty-seven pesticides were tested for possible interference
    in this GLC method of analysis. It found that none of the pesticides
    studied eluted at the same elution time as did captafol under the
    conditions employed, and therefore there would be no interference from
    any of them. The sensitivity of 0.01 ppm can be obtained by the GLC
    method (Kilgore and White, 1967).

    The analytical method for the analysis of dichloroacetic acid which is
    a demonstrated hydrolysis product of captafol, is based upon
    microcoulometric gas chromatography. This method of analysis is both
    highly specific and quite free from interfering material. The limit of
    detection of this method is approximately 0.05 ppm, or possibly lower.
    The sample is macerated and extracted with water. The water extract is
    then extracted with ether. The DCAA in the ether layer is esterified
    with diazomethane and the analysis completed with the microcoulometric
    gas chromatography (Anon., 1965c).

    The hydrolysis products of the imide portion of the captafol molecule,
    tetrahydrophthalimide and tetrahydrophthalic acid, are detected by a
    method which involves the extraction, cleanup, and esterification of
    the acid derivatives with diazomethane and the subsequent gas
    chromatographic detection of the esters. The detection system used is
    hydrogen flame. This method is quite specific but great care must be
    taken to eliminate interfering materials which would be detected by
    the hydrogen flame. With adequate cleanup on most crops, this method
    is sensitive to approximately 0.05 ppm (Anon., 1966c).


        TABLE II
                                                                                                     

    Data on captafol residues and its degradation products in various fruits (Anon., 1969

    Crop      Rate of                      Pre-                      Residue*
              application                  harvest                     (ppm)             Tetra-
              (kg a.i.       No. of        interval                    Tetra-         hydrophthalic
              per ha)        treatments    (days)     Captafol    hydrophthalimide        acid
                                                                                                     

    Peach       9.0             12            1          3.4            1.0                0.5
                                              7          3.5            1.1                0.3

                3.1              4            1         11.7            0.00               0.00
                                              5         12.0            0.00               0.00
                                             10          9.9            0.00               0.00
                                             15          9.3            0.00               0.00

                3.1              4            1         20.6            0.00               0.00
                                              5         13.0            0.00               0.00
                                             10         13.0            0.00               0.00
                                             15         10.6            0.00               0.00

    Cucumber    1.8              6            1          0.14           0.00               0.06
                                              6          0.10           0.00               0.13

    Tomato      2.7              9            1          9.7            0.16               0.00
                                              7         10.1            0.16               0.07

                2.7              9            1          5.2            0.27               0.00
                                              7          4.3            0.20               0.00
                                                                                                     
    * No dichloroacetic acid is detected

    TABLE III
                                                                                                                

    Comparison of captafol residues of fresh and processed fruits (Anon., 1969)

    Crop      Rate of                                 Pre-                        Residue*
              application                             harvest                       (ppm)            Tetra-
              (kg a.i.       No. of                   interval                      Tetra-        hydrophthalic
              per ha)        treatments    Product    (days)      Captafol    hydrophthalimide        acid
                                                                                                                

    Peaches     7.1              1         fresh       139          0.00
                                           dried                    0.14

    Plums       4.7-6.2          2         fresh       139          0.00
                                           dried                    0.42

               15.6-3.9          3         fresh       139          0.00
                                           dried                    0.19

    Peaches     2.4-3.9          7         canned        1          0.1             1.6                0.0
                                 6                       6          0.0             0.1                0.1
                                 5                      15          0.0             0.1                0.1
                                 4                      22          0.0             0.0                0.1
                                 3                     150          0.0             0.0                0.1

    Tomatoes    2.7              5         canned    (   1          0.44            0.08               0.00
                                           juice     ( 180          0.13            0.00               0.03

                2.7              5         canned        1          0.15            0.00               0.00
                                           juice

                                           canned        1          0.68            0.10               0.00
                                           puree

                                           canned      180          0.00            0.05               0.00
                                           juice

                                           canned      180          0.16            0.20               0.00
                                           puree

    TABLE III (cont'd)
                                                                                                                

    Comparison of captafol residues of fresh and processed fruits (Anon., 1969)

    Crop      Rate of                                 Pre-                        Residue*
              application                             harvest                       (ppm)            Tetra-
              (kg a.i.       No. of                   interval                      Tetra-        hydrophthalic
              per ha)        treatments    Product    (days)      Captafol    hydrophthalimide        acid
                                                                                                                

                2.7             10         fruit         1          0.48            0.12               0.08
                                                         7          0.13            0.06               0.00
                                           canned        1          0.16            0.07               0.00
                                           juice
                                           canned        1          0.23            0.07               0.00
                                           puree
                                           canned      180          0.00            0.00               0.00
                                           juice
                                           canned      180          0.00            0.12               0.00
                                           puree

                0.9                        canned        1          0.02
                                           concentrate
                                                                                                                

    * No dichloroacetic acid is detected
    

    The GLC method is considered most suitable for regulatory purposes,
    but the TLC method could also be applied.

    NATIONAL TOLERANCES

                                                                      

        Country                Crop                     Tolerance (ppm)
                                                                      

    Australia            Stone fruit                           20
                         Other fruit and vegetables            5

    Canada               Cherries (sour)                       50
                         Apricots, nectarines, peaches         30
                         Tomatoes                              15
                         Cherries (sweet), cucumbers,          5
                           melons, plums, prunes

    Switzerland          Grapes, strawberries                  5

    United States of     Cherries (sour)                       50
    America              Apricots, peaches                     30
                         Tomatoes                              15
                         Melons                                5
                         Cherries (sweet), cucumbers,          2
                           nectarines, plums (fresh prunes)
                                                                      

    APPRAISAL

    Captafol is used to control fungus diseases on tree fruits, melons,
    cucurbits, tomatoes, and potatoes. In the case of peaches, apricots,
    nectarines, cherries, plums and prunes, a dormant or blossom
    application is recommended. In addition, seasonal foliar applications
    are recommended for certain crops. In-furrow spray applications are
    recommended for the control of representative diseases on cotton.

    Captafol is used for foliage application at a rate of 0.05 to 0.2
    percent of active ingredient wettable powder of flowable suspension in
    spray. It is quite stable except under alkaline conditions.

    Tolerances established in the U.S.A., Canada, Switzerland and
    Australia vary from 2 to 50 ppm.

    The residue data of captafol available to the meeting are only from
    treatments made under commercial conditions in the U.S.A. The initial
    residue of captafol is reduced by one half generally within a week or
    two. The residue is mainly on the surface of the fruit.

    The two major routes of degradation in plants are the same as those in
    animals, namely reactions with sulfhydryl compounds and hydrolysis.
    Sulfhydryl reaction is more rapid than hydrolysis. Main degradation
    products are tetrahydrophthalimide and tetrahydrophthalic acid.
    Dichloracetic acid has not been found.

    In thermal food processes as well as in macerated plant materials,
    captafol is extensively decomposed. Decomposition products,
    tetrahydrophthalimide and tetrahydrophthalic acid, may appear in
    processed foods at the beginning of the storage period.

    Captafol is found to degrade rapidly in natural soils.

    Two methods are reported to be available for the analysis of captafol
    residues in plant and animal tissues. The preferred method is GLC. The
    alternate procedure is based on thinlayer chromatography, the
    sensitivity of which is about 0.03-0.05 ppm, depending on the crop
    interferences.

    RECOMMENDATIONS FOR TOLERANCES, TEMPORARY TOLERANCES OR PRACTICAL 
    RESIDUE LIMITS

    TEMPORARY TOLERANCES

    Residues resulting from good agricultural practice as follows are
    recommended, effective till 1973:

                                                                                        
                                                   Pre-harvest    Captafol residue
          Crop                Comment            interval (days)         (ppm)
                                                                                    

    Melons, whole                                     1                   2

    Cucumbers, whole                                  1                   1

    Tomatoes                                          1                   5

    Peaches                                           10-14              15

    Cherries, sour       Foliar application           20                 10

    Cherries, sweet      Blossom application          45-70               2

    Apricots             Blossom application          100                 0.5

    Plums                Blossom application          130-140             0.2
                                                                                    
    
    The data on pineapples, apples and grapes were inadequate for
    evaluation.

    FURTHER WORK OR INFORMATION

    REQUIRED (before 30 June 1973)

    1. Studies to elucidate the effects seen in the teratogenicity
       experiments.

    2. Data from countries ether that the United States of America on the
       required rates and frequencies of application, pre-harvest 
       intervals, and the resultant residues.

    3. Data on residue levels in raw agricultural commodities moving in
       commerce.

    4. Data on the effect of washing, peeling and blanching on the residue
       levels of various crops.

    5. Elucidation of the histopathology of the kidney and liver in the
       rat.

    DESIRABLE

    1. Metabolic studies to provide further information on the absorption
       and distribution after oral administration and to identify the
       metabolites found in animal tissues.

    2. Collaborative studies to establish a regulatory method for captafol
       in the presence of captan and folpet.

    REFERENCES

    Anon. (1964) Difolatan residue analysis - cleanup procedure for oily
    materials. Addendum to RM-6. Chevron Chemical Co. Unpub. Rept.

    Anon. (1965a) The reaction of Difolatan with sulfhydryl compounds.
    Chevron Chemical Co. Unpub. Rept.

    Anon. (1965b) Difolatan residue analysis by electron capture gas
    chromatography. Method RM-6B. Chevron Chemical Co. Unpub. Rept.

    Anon. (1965c) Difolatan metabolism - The analysis of residues of
    dichloroacetic acid using microcoulometric gas chromatography. Method
    RM-6C. Chevron Chemical Co. Unpub. Rept.

    Anon. (1966a) Studies on the uptake of Difolatan by root crops grown
    in soils treated with Difolatan. Chevron Chemical Co. Unpub. Rept.

    Anon. (1966b) Difolatan residue analysis - thin layer chromatographic
    method. Method RM-6. Chevron Chemical Co. Unpub. Rept.

    Anon. (1966c) The analysis of residues of Difolatan and two
    tetrahydrophthalic acid derivatives. Residue Method RM-6D. Chevron
    Chemical Co. Unpub. Rept.

    Berteau, P.E. (1963) Difolatan - a preliminary report on its
    hydrolysis and related reactions. Chevron Chemical Co. Unpub. Rept.

    Berteau, P.E., Pack, D.E., Ospenson, J.N. and Crossley, J. (1966) The
    metabolism of Difolatan.  Paper presented at the American Chemical
    Society, Western Regional Meeting. San Francisco, California, 18
    October 1966 [Abstracted in Vortex, (Publication of the California
    section, American Chemical Society) 27, insert P. 37 (1966)]

    Berteau, P.E. and Pack, D.E. (1966a) The degradation of Difolatan in
    soils. Chevron Chemical Co. Unpub. Rept.

    Berteau, P.E. and Pack, D.E. (1966b) Difolatan degradation in
    soil-studies on the formation and decay of dichloroacetic acid.
    Chevron Chemical Co. Unpub. Rept.

    Berteau, P.E. and Pack, D.E. (1966c) The movement of Difolatan through
    soil columns. Chevron Chemical Co. Unpub. Rept.

    Cabral, R.V. de G. and Tomes, I.L. (1966) Fungicidal assay against
    Botrytis cinerea and the effects of fungicides on must fermentation.
    An. Inst. Super. Agron., Univ. Tec. Lisboa 29:279-97 (Chem. Abstr.
    70:46363 u, 1969)

    Cervenka, H., Key, J.H. and Calandra, J.C. (1964) Chronic oral
    toxicity of RE 5865-Beagle dogs. Unpub. Rept. of Industrial Bio-Test
    Laboratories submitted by Chevron Chemical Co.

    Chalkov, I. and Vanev, S. (1968) Determination of the effect of some
    new fungicides, used to control gray rot in grapes under field
    conditions, on the enzymic activity of yeasts. Lozarstvo Vinar (Sofia)
    17:33-40 (Chem. Abstr. 69:34908 s, 1968)

    Dye, D.F. (1969) Difolatan(R). Unpub. Rept. prepared and submitted by
    Chevron Chemical Co.

    Ives, M. and Calandra, J.C. (1965) Teratogenic study on difolatan.
    Unpub. Rept. of Industrial Bio-Test Laboratories submitted by Chevron
    Chemical Co.

    Jackson, G.L., Fancher, O.E. and Calandra, J.C. (1967) Rabbit
    teratogenic study. Difolatan. Unpub. Rept. of Industrial Bio-Test
    Laboratories submitted by Chevron Chemical Co.

    Kennedy, G., Fancher, O.E., and Calandra, J.C. (1966) Three-generation
    reproduction study on difolatan - Albino rats. Unpub. Rept. of
    Industrial Bio-Test Laboratories submitted by Chevron Chemical Co.

    Kennedy, G., Fancher, O.E. and Calandra, J.C. (1968a) An investigation
    of the teratogenic potential of captan, folpet and difolatan. Toxicol.
    appl. Pharmacol. 13:421-30

    Kennedy, G., Fancher, O.E and Calandra, J.C. (1968b) Teratologic
    investigation of difolatan in Macaca mulatta (Rhesus monkey). Unpub.
    Rept. of Industrial Bio-Test Laboratories submitted by Chevron
    Chemical Co.

    Kilgore, W.W. and White, E.R. (1967) Determination of Difolatan
    residues in fruits by electron-capture gas chromatography. J. Apr.
    Food Chem. 15:1118-20

    Kohn, F.E., Key, J.H. and Calandra, J.C. (1964) Two-year chronic oral
    toxicity of RE 5865 Albino rats. Unpub. Rept. of Industrial Bio-Test
    Laboratories submitted by Chevron Chemical Co.

    Kohn, G.K. (1965) Present status of metabolic fate studies of
    Difolatan. Unpub. Rept. of Chevron Chemical Corporation for
    presentation at the Orthocide Conference, Amsterdam, 29 November - 5
    December 1965

    Leary, J.B. (1966) Difolatan: shay rat tests. Unpub. Rept. of Chevron
    Chemical Co. (cited by Crossley, 1967 - see the monograph of captan)

    Ogawa, J.M., Boyack, G.A., Sandeno, J.L., and Mathre, J.H. (1964)
    Control of postharvest fruit decays in relation to residues of
    2.6-dichloro-4-nitroaniline and Difolatan. Hilgardia 35:365-73

    Palazzolo, R.J., Key, J.H. and Calandra, J.C. (1964) Acute toxicity
    studies on Difolatan 80W. Unpub. Rept. of Industrial Bio-Test
    Laboratories submitted by Chevron Chemical Co.

    Palazzolo, R.J., Kay, J.H. and Calandra, J.C. (1965a) Acute oral
    toxicity on RE 5865. Unpub. Rept. of Industrial Bio-Test Laboratories
    submitted by Chevron Chemical Co.

    Palazzolo, R.J., Key, J.H. and Calandra, J.C. (1965b) Acute oral
    toxicity on RE 5865 (aqueous suspension). Unpub. Rept. of Industrial
    Bio-Test Laboratories submitted by Chevron Chemical Co.

    Palazzolo, R.J., Fancher, O.E. and Calandra, J.C. (1966) Rabbit
    reproduction study, THPI. Unpub. Rept. of Industrial Bio-Test
    Laboratories submitted by Chevron Chemical Co.

    Pomerantz, I.H. and Ross, R. (1968) Captan and structurally related
    compounds: thin-layer and gas-liquid chromatography. J. Assoc. Offic.
    Anal. Chem. 51:1058-62

    Potter, J.L. (1964) Studies on the hydrolysis of Difolatan in a
    homogeneous aqueous-acetone buffer system under neutral pH conditions.
    Chevron Chemical Co. Unpub. Rept.

    Potter, J.L. (1965) Preliminary studies on the in vitro degradation of
    Difolatan by crop macerates and filtrates. Chevron Chemical Co. Unpub.
    Rept.

    Turner, P. D. (1969) Evaluation of fungicides for the control of
    Helminthosporium heveae on Hevea rubber in Malaysia. I. Laboratory
    assessment. Experimental Agriculture 5:33-40

    Verrett, M.J., Mutchler, M.K., Scott, W.F., Reynaldo, E.F. and
    McLaughlin J. (1969) Teratogenic effects of captan and related
    compounds in the developing chick embryo. Annals N.Y. Acad. Sci.
    160.334-43
    


    See Also:
       Toxicological Abbreviations
       Captafol (HSG 49, 1990)
       Captafol (ICSC)
       Captafol (PIM 097)
       Captafol (WHO Pesticide Residues Series 3)
       Captafol (WHO Pesticide Residues Series 4)
       Captafol (Pesticide residues in food: 1976 evaluations)
       Captafol (Pesticide residues in food: 1977 evaluations)
       Captafol (IARC Summary & Evaluation, Volume 53, 1991)