FAO/PL:1968/M/9/1 WHO/FOOD ADD./69.35 1968 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 Committee on Pesticide Residues, which met in Geneva, 9-16 December, 1968. FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS WORLD HEALTH ORGANIZATION Geneva, 1969 DICOFOL IDENTITY Chemical names 1,1 bis (4-chlorophenyl) 2,2,2-trichloroethanol; 2,2,2,-trichloro-1, 1-di (4-chlorophenyl) ethanol (IUPAC). Synonyms Kelthane(R) FormulaOther information on identity and properties Analysis of technical dicofol is not known. Purity of technical dicofol is 82-88 per cent. The United States Department of Agriculture (USDA, 1968a) places the total acaricide market for 1964 in the United States of America at about three million pounds active ingredients per year, dicofol being about half of that amount. Resistance is still today a cause for reduction of the use of dicofol, e.g. in Israel. EVALUATION FOR ACCEPTABLE DAILY INTAKE Biochemical aspects No specific identification of the metabolites of dicofol in animals has been made. However, on the basis of the known chemistry of the compound, 4,4'-dichlorobenzophenone is considered to be a probable metabolite. Thus, under alkaline conditions, dicofol is hydrolytically cleaved to 4,4'-dichlorobenzophenone and chloroform (Rohm and Haas, 1968). Upon ingestion of dicofol by mammals, storage of the compound occurs in the adipose tissue. Rats were fed dicofol at a level of 32 ppm in their diet for 12 weeks. After eight weeks the level of the compound in the fat had reached equilibrium at concentrations of 25 ppm for the males and 70 ppm for the females, which amounts corresponded to 75 per cent and 200 per cent of the dietary levels. After 12 weeks, dicofol was withdrawn from the diet and the level of stored material declined. The rate of decline was greater for the male animals than for the females. By 14 weeks after withdrawal the level of dicofol in the fat was zero for the males but still remained at about 6 ppm for the females. Feeding with higher or lower dose levels also showed that dicofol was stored in the fat of the female rat to a greater degree than in the male (Smith et al., 1959). The effect of dicofol on plasma 17-hydroxy-corticosteroids in the dog was determined on two dogs which were fed 300 ppm and 900 ppm over two separate periods of one to two months' duration. The ability of the adrenal cortex to elaborate 17-hydroxy-corticosteroids in response to ACTH stimulation was slightly reduced at the 300 ppm level and markedly reduced at the 900 ppm level. The results also showed that following this treatment with dicofol, the ability of the adrenal gland to return to the pre-treatment level of response to ACTH proceeded slowly and, possibly, incompletely (Smith et al., 1959). Acute toxicity (80 per cent technical product) LD50 mg/kg Animal Route body-weight Reference Rat (M) Oral 809 Smith et al., 1959 Rat (F) Oral 684 Smith et al., 1959 Rabbit (M) Oral 1810 Smith et al., 1959 Dog (mixed) Oral >4000 Smith et al., 1959 Short-term studies Rat Dicofol was fed to groups, each containing 10 male and 10 female rats, for 90 days at dietary concentrations of 0, 20, 100, 500, 1250 and 2500 ppm. Survival was adversely affected at 1250 ppm and above. Growth was inhibited at 100 ppm and higher levels in the females but only at 1250 ppm in the males. Increased liver to body weight ratios occurred in the survivors in both sexes. Liver lesions were the most consistent histopathological finding, but were only of scattered incidence at dose levels below 1250 ppm (Smith et al., 1959). Groups containing equal numbers of male and female rats were fed 0, 2, 5, 10, 15 and 20 ppm in their diets for 55 weeks. Growth, survival and liver to body weight ratios were not affected at any dose level (Smith et al., 1959). Five groups, each of 10 male and 10 female rats were fed 0, 50, 200, 1000 and 3000 ppm in their diet for 13 weeks. Body weight and food intake were reduced at the 200 ppm level and above, and at 3000 ppm there was 100 per cent mortality. Haematological criteria were comparable to the controls. Organ to body weight ratios were increased in the case of the liver at the 200 ppm level and above and in the case of the thyroid at the 1000 ppm level. Decreased uterus and prostrate to body weight ratios were observed at 1000 ppm. Liver glucose-6-phosphatase was depressed at 1000 ppm. while hexobarbital oxidase activity showed a dose-related stimulation in all treated groups. Histopathological examination revealed enlargement of centrilobar cells and nuclei at 200 ppm and above. Electron microscopy revealed smooth endoplasmic reticulum whorls to be present only at 1000 ppm and above (Verschuuren et al., 1968). Dog Groups each containing three dogs were given levels of dicofol of 100, 300 and 900 ppm for one year. Survival was affected only at 900 ppm. Body weight gain was normal and haematological and histological observations revealed no pathological effects (Smith et al., 1959). Long-term studies Rat Dicofol was fed to 60 groups, each containing 10 male and 10 female rats, at dietary levels of 0, 20, 100, 250, 500 and 1000 ppm for two years. Growth depression occurred in male rats at 500 and 1000 ppm, and in female rats progressively with increasing dietary concentration at 250, 500 and 1000 ppm. A growth depression after three months, recorded in female rats at 20 ppm (but not at 100 ppm) has not been observed again in later studies. Absolute organ weights showed no significant differences from the controls, with the exception of an increase in the case of the livers and kidneys of the female rats fed 1000 ppm. Organ to body weight ratios were significantly increased for the liver at 250 ppm and for the liver, kidney and heart at 500 ppm in the females, but only for the liver at 500 ppm in the males. Histopathological findings were confined to hydropic changes in the liver which were regarded as reversible (Larson, 1957). Special studies (a) Reproduction Mouse. Groups of varying numbers of mice were maintained throughout five generations on dietary levels of 0, 7, 25, 100, 225 and 500 ppm of dicofol. At the 500 ppm level the litter sizes, average weight of the pups and also the values for fertility, viability and lactation indices were lower than for the control group. However, all these parameters were normal for the 225 ppm and lower levels (Brown, 1967a). Rat. Four groups, each of 27 male and 27 female rats were fed dietary levels of 0, 100, 500 and 1000 ppm of dicofol in a two-generation reproduction study. There were no F1b pups surviving at 21 days when the original parents were fed 500 or 1000 ppm. Litter size from the 1000 ppm group was similar to the controls but over-all mortality in the pups was greater. Considerable reduction in fertility of the animals fed 500 and 1000 ppm was evident. No congenital defects were observed in any of the F2a or F2b animals (Brown, 1964-65). Groups of rats were maintained on diets containing 25 or 75 ppm of dicofol through a three-generation study. The average number of pups born per litter to parents receiving 75 ppm was slightly lower than for the controls. There was no compound related effects relative to body weight, fertility, gestation, viability or lactation indices at either level, nor were there any congenital abnormalities evident in either the viable or the still-born pups (Brown, 1967b). (b) Toxicity study of a possible metabolite The possible metabolite, 4,4'-dichlorobenzophenone was fed to groups each containing 15 male and 15 female rats, at dietary levels of 0, 100 and 1250 ppm for three months. No effects were noted at either level except somewhat reduced heart to body weight ratios found in the males receiving 1250 ppm, but not in the females (Larson, 1965). Comments Short-term experiments on dogs and rats, reproduction studies on rats and mice and long-term experiments on rats are reported. From the results of the acute and short-term experiments a great species difference in susceptibility is evident between dogs and rats. No specific identification of possible metabolites has been made in animals but dichlorbenzophenone is a probable metabolite. No human studies have been reported. Comparative metabolic studies in animals and man, including adrenal function studies after oral administration are desirable. TOXICOLOGICAL EVALUATION Level causing no significant toxicological effect Rat: 50 ppm, equivalent to 2.5 mg/kg per day. Estimate of acceptable daily intake for man 0.0-0.025 mg/kg body weight. RESIDUES IN FOOD AND THEIR EVALUATION Use pattern Pre-harvest treatments Kelthane is a miticide with systemic properties, used on a large number of crops. It has no insecticidal activity. The following table gives a review of application rates of dicofol and recommended pre-harvest intervals. Rate of application (kg/ha) Pre-harvest interval Crop Small plants Large plants (days) Apples, pears, crabapples, 2.20 4.41-5.30 7 quince Cherries 2.20 3.96 7 Peaches, apricots, 2.20 3.96 14 nectarines Walnuts, filberts, pecans, chestnuts, hickory nuts 1.76 4.85 14 and almonds, if hulls are not fed to livestock Almonds, if hulls are fed 1.76 3.09 Before nut to livestock formation Grapes, hops .66 1.60 7 Strawberries .44 2.96 2 Raspberries and other cane .66 1.60 2 berries Beans .44 .73 7 Beans (dry) .44 1.00 45 Beans (California) .66 1.32 45 Cantaloupe, cucumbers, pumpkins, squash, melons, .44 .73 2 water melons Tomatoes, peppers .66 1.00 2 Alfalfa, clover, other .66 1.32 legumes for seed only Corn (field) .88 1.76 Before ears form Plums, prunes, figs 1.76 2.50 7 (Adapted from Rohm and Haas, Kelthane 35 label) Post-harvest treatments No post-harvest uses of dicofol are known. Other uses Dicofol is used for control of mites on lawns, ornamentals and shade trees, as well as against clover mites in buildings. Residues resulting from supervised trials Detailed residue data are available from United States trials with dicofol on important crops and have been deposited with FAO. Rates of application were similar to those given above. The typical data presented below are representative: Crop Number of Post-treatment Residue (ppm) treatments interval (days) Range Average Almonds (whole) 1 129-157 3.11-0.18 1.60 Apples 1 7 1.1 Beans (whole) 1 6 2.45 Carrots (roots) 1-2 5 0.00-0.25 0.10 Celery 1 6 1.32-4.45 2.88 Cherries 1 7 1.2 -1.8 1.5 Citrus (whole) 1-2 7 1.12-5.0 2.2 Cottonseed 1 15-76 0.00-0.1 0.0 Cucumbers 1 2 0.7 -2.3 1.6 Figs 1 7 1.86-5.32 3.92 Grapes 1 5 0.89-2.21 1.64 Hops (green) 1 7 3.0 -7.9 5.4 Lettuce 2 2 1.10-9.87 5.59 Mint (fresh hay) 1 7 35.8 -38.9 37.3 Peaches 1 14 4.9 -6.8 5.7 (continued) Crop Number of Post-treatment Residue (ppm) treatments interval (days) Range Average Pears 2 7 1.1 -2.6 1.9 Pineapples 4 5 0.0 -0.05 <0.05 (pulp) Plums, prunes 1 9 0.06-0.16 0.11 Raspberries 1 2 2.7 Spinach 1 4 2.88-3.90 3.39 Strawberries 1 3 0.13-0.90 0.37 Tea, raw leaves 1 7 18.00-31.00 25.0 1 7 0.00-18.5 5.1 Tomatoes 1 1 0.5 -0.57 0.53 Tropical fruits 5 4 0.0 0.0 Walnuts 1 7 0.57-0.92 0.86 Water melons 1 20 0.0 (heart) Although dicofol is used for seed treatment no data on residues are available. Fate of residues In soils Dicofol is not used against pests in soil, but studies have been conducted to determine residues in soil resulting from spray application on crops. Dicofol residues in soil decrease rapidly at first, then more slowly. After three monthly applications of 2.56 kg/ha, residues which had reached 1.13 ppm decreased to 0.25 ppm after 636 days, (Rohm and Haas, 1967). In plants No information is available on metabolism in plants. In animals Cows fed 2 ppm dicofol for 71 days averaged from 0.23-0.40 ppm residues in their milk; when the same cows were fed 1.0 ppm, the level was not detectable. Two body fat samples taken at the end of the study contained 1.1 and 2.7 ppm (Zweig et al,, 1963). A "Blue" cow fed 5 ppm dicofol for 17 days, excreted a maximum of 0.022 ppm dicofol per se and a maximum of 0.55 ppm dicofol plus metabolites in the milk. Plateau values were obtained about six days after start of dicofol feedings, and initial decay was also rapid. From the fifth day after withdrawal of dicofol, the amounts of material excreted were small, and the rate of decrease became low. In a "White" cow fed 30 ppm dicofol for three days, 0.68 ppm dicofol were found in kidney fat. Dicofol metabolites were found in kidney fat, liver, udder, brain, kidney lungs, blood, heart, omentum, bone marrow and muscles (Rohm and Haas, 1968). The feeding of dicofol to steers produces no significant residues in body fat at a level of 0.75 and 1.5 ppm. A feeding level of 3.0 ppm produces a definite residue of 0.32 ppm (Peoples, 1967). In tissues, milk and urine of a cow fed dicofol two groups of metabolites were found, one more polar than dicofol and one less polar. The metabolites of the first group were not identified. In the second group, two substances were identified as 1,1 bis (4-chlorophenyl) 2-chloro-ethylene and as 1,1 bis (4-chlorophenyl)-2,2-dichloro-ethylene. Sixty per cent of total milk residues is due to the latter substance, but it is suggested that it may be present in technical dicofol rather than result from the metabolic reduction of dicofol itself (Rohm and Haas, 1958). The latter two compounds were also found as metabolites of DDT. In storage and processing Residues on fruits are reduced by washing. Wash-water of oranges contained up to 0.05 ppm dicofol; 0.12-0.57 ppm remained in the peel. Unwashed raspberries contained 0.7-2.9 ppm dicofol, residues which were reduced to 0.7-1.4 after washing. Peeling reduces residues to values below 1 ppm: Fruit Residue (ppm) Peel Pulp Citrus fruit 0.29-12.0 0-0.27 Almonds 0-12.2 0-0.03 Cucumbers 0.09-0.4 0-0.17 Pineapples 5.5 -24.2 0-0.05 Tropical fruit 4.2 -9.7 0 (Rohm and Haas, private communication) In canned or frozen fruits dicofol was found only in 1.3 per cent of domestic samples, with an average ppm of 0.01. No dicofol was found in samples imported into the United States of America (USDA, 1968b). Brewed tea contained residues up to 0.0085 ppm. Under rigorous treatment, such as preparing instant tea from tea leaves, or distilling oil from mint leaves, dicofol may be broken down to p,p'-dichlorobenzophenone and chloroform (Rohm and Haas, private communication). Evidence of residues in food in commerce or at consumption Examination of market samples of food in the United States of America showed that dicofol residues were found in 0.7 per cent of domestic samples and 1.8 per cent of imported samples (Duggan and Dawson, 1967a). In fruit the following concentrations were found in the United States of America from 1964 to 1967 (USDA, 1968b). Domestic samples Imported samples Fruit Incidence Average Incidence Average per cent. (ppm) per cent. (ppm) Small fruit (strawberries, cherries, plums, 5.1 0.03 2.1 0.02 grapes, cranberries, etc.) (continued) Domestic samples Imported samples Fruit Incidence Average Incidence Average per cent. (ppm) per cent. (ppm) Large fruit (apples, 8.6 0.02 3.3 0.01 oranges, pears, peaches, etc.) Total diet studies in the United States of America from 1964 to 1967 showed the following results (Duggan and Weatherwax, 1967b; USDA, 1968b) Year Positive per cent. Daily average composites intake (mg) 1964-1965 0.5 0.003 1965-1966 3.7 0.002 1966-1967 5.6 0.012 In 41.9 per cent of fruit-composites (apples, oranges, pears, peaches, etc.) dicofol was found in an average concentration of 0.031 ppm (USDA, 1968b). Dietary intake of dicofol in the United States of America was 0.00004 mg/kg body weight/day in 1965; 0.00015 in 1966 and 0.00018 in 1967 with an average of 0.00013 for three years (USDA, 1968b). In Canada 60 restaurant meals were examined. Dicofol was found in an average concentration of 0.07 ppm in fruit and fruit salads, in legumes, 0.08 ppm whereas only traces were found in milk (Swackhamer, 1965). Methods of residue analysis The methods are adequate for present purposes. Methods for colorimetric determination of dicofol are based on the method of Rosenthal, 1957. Dicofol is converted to chloroform with alkali. Chloroform is separated from extraneous materials and produces, with a water-pyridine-sodium-hydroxide mixture, a Fujiwara-type red dye, which is read at 535mµ against a pyridine blank. This method may be used for residue determination in plants, fruit and vegetables and has been simplified for analysis of milk (Gordon, 1963). Residues in crops and soil may also be determined, after chromatographical clean-up, by GLC using an electron capture detector (Morgan, 1967). An ultra-violet spectrophotometric method involves hydrolysing the dicofol to 4,4'-dichlorobenzophenone (Gunther and Blinn, 1957). A method omitting the hydrolysis step and allowing the dicofol to be oxidized to non-interfering compounds permits the measurement of 4,4'-dichlorobenzophenone present in mint-oil and mint-hay (Rohm and Haas, private communication). The sensitivity of the analytical procedures is 0.01 ppm. National tolerances Tolerance Pre-harvest Country Crop (ppm) interval (days) United States Berries 5 of America German Federal Fruit, including Republic grapes and hops 0.5 14 Vegetables 0.5 Beans 14 Cucumbers 4 RECOMMENDATIONS FOR TOLERANCES AND PRACTICAL RESIDUE LIMITS Appraisal Dicofol is used exclusively to control phytophagous mites and although closely related to DDT has virtually no insecticidal activity. Its principal use is on apples, grapes and hops in Europe and North America, and tea (spot treatments only) in the Far East, with some minor use on citrus in these same areas. In North America, the rates and frequencies of application are generally greater than in other countries because of more serious mite problems. It is not used on animals. Dicofol is a technical product containing 82-88 per cent of the pure (active) compound. The impurities are known and their relative concentration are constant. The data available to the meeting were obtained solely in the United States of America and did not include information about uses elsewhere or figures for residues after such use, although figures were available for some imports into the United States of America. Very little is known about the metabolism of dicofol in plants and animals. In animals, dicofol can be found as such together with various metabolites. Precise figures for the amounts of these compounds in experimental plants or animals, either from a single or from repeated applications, have not been published. 1,1 bis (4-chlorophenyl) 2-chloro-ethylene and 1,1 bis (4-chlorophenyl-2,-2-dichloro-ethylene) have been identified as metabolites in animals. However, the latter may be present in the technical product used. In mint oil and tea, 4,4-dichlorobenzophenone has been identified. The literature includes methods of residue analysis which measure dicofol alone or together with some breakdown products. For the determination of dicofol alone the sensitivity is 0.01 ppm. However, no referee method of analysis has been evaluated. Recommendations Temporary tolerances The following temporary tolerances (to be in effect until 1972) are to apply to raw agricultural products moving in commerce unless otherwise indicated. In the case of fruit and vegetables the tolerances should be applied as soon as practicable after harvest and in any event prior to actual retail to the public. In the case of commodities entering international trade, the tolerances should be applied by the importing country at the point of entry or as soon as practicable thereafter. Fruit, vegetables, hops, tea (from a particular estate, for blending only) 5 ppm Tea (blended) 1 ppm Further work or information Required before 30 June 1972: 1. Data from countries other than the United States of America on the required rates and frequencies of application, pre-harvest intervals, and the resultant residues. 2. Information on the nature of the terminal residues in plants, animals, and their products. Desirable: 1. Collaborative studies to establish a referee method. 2. Comparative metabolic studies in animals and man, including adrenal function studies after oral administration. REFERENCES Brown, J. R. (1964-65) Toxicologic studies on the effects of kelthane in the diet of albino rats on reproduction (first interim, second interim and final reports). Departments of Physiological Hygiene, University of Toronto. Unpublished reports Brown, J. R. (1967a) Toxicological studies on 2,2-bis-chlorophenyl-2,2,2-trichloroethanol, kelthane. Brown Biological Laboratories Ltd. Unpublished report Brown, J. R. (1967b) Three-generation reproduction study on rats receiving technical kelthane in their diet. Department of Physiological Hygiene, University of Toronto. Unpublished report Duggan, R. E. and Dawson, K. (1967a) Pesticides: A report on residues in food. FDA Papers, 1: 2-5 Duggan, R. E. and Weatherwax, J. R. (1967b) Dietary intake of pesticide chemicals. Science, 157: 1006-1010 Gordon, C. F., Haines, L. D. and Martin, J. J. (1963) Acaricide residues: An improved method for kelthane residue analysis with applications for determination of residues in milk. J. Agr. Food Chem., 11: 84-86 Gunther, F. A. and Blinn, R. C. (1957) Ultraviolet spectrophotometric microdetection of the acaricide 4,4'-dichloro-alpha-(trichlormethyl) benzhydrol (SW 293). J.Agr. Food Chem., 5: 517-519 Larson, P. S. (1957) Two-year study on the effect of adding kelthane to the diet of rats. Medical College of Virginia. Unpublished report Larson, P. S. (1965) Toxicologic study on the effect of adding dichlorobenzophenone to the diet of rats for a period of three months. Department of Pharmacology. Medical College of Virginia. Unpublished report Morgan, N. L. (1967) The identification and relative retention times of p,p'-kelthane and its breakdown product p,p'-dichlorobenzophenone using GLC. Bull. environ. Contam. Toxicol., 2: 306-312 Peoples, S. A. (1967) Residues in the body fat of steers fed kelthane in their ration. Dept. of Physiol. Sci. School of Veterinary Medicine, University of California, Davis. Unpublished report Rohm and Haas. (1958) Research Reports 13-27 and 11.141. Robin and Haas Co. Rohm and Haas. (1967) RAR Memorandum 521. Rohm and Hass Co. Rohm and Haas Co. (1968) Kelthane. Unpublished report Rosenthal, J., Frisone, G. J. and Gunther, F. A. (1957) Colorimetric microdetermination of the acaricide 4,4'-dichloro-alpha-(trichloromethyl) benzhydrol (FW-293).J. Agr. Food Chem., 5: 514-517 Smith, R. B. Jr, Larson, P. S., Finnegan, J. K., Haag, H. B., Hennigar, G. R, and Cobey, F. (1959) Toxicologic studies on 2,2 bis-(chlorophenyl)-2,2,2-trichloroethanol (kelthane). Toxicol. appl. Pharmacol., 1: 119-134 Swackhamer, A. B. (1965) Report on pesticide residues in restaurant meals in Canada. Food and Drug Directorate, Department of National Health and Welfare, Ottawa, Canada. Pesticide Progress, 3: 108-114 USDA. (1968a) Agricultural Economic Report 131 USDA. (1968b) United States Department of Health, Education and Welfare. The regulation of pesticides in the United States Verschuuren, H. G., Kroes, R. and den Tonkelaar, E. M. (1968) Toxiciteitsonderzoek met kelthaan bij ratten gedurende 90 dagen (Toxicity experiment with kelthane in rats of 90 day duration). National Institute of Public Health, Utrecht. Unpublished report Zweig, G., Pye, E. L. and Peoples, S. A. (1963) Residues in butter fat and body fat of dairy cows fed at two levels of kelthane (1.0 and 2.0 ppm). J. Agr. Food Chem., 11: 72-79
See Also: Toxicological Abbreviations Dicofol (ICSC) Dicofol (AGP:1970/M/12/1) Dicofol (WHO Pesticide Residues Series 4) Dicofol (Pesticide residues in food: 1992 evaluations Part II Toxicology) Dicofol (IARC Summary & Evaluation, Volume 30, 1983)