AGP:1970/M/12/1 WHO/FOOD ADD/71.42 1970 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, 9-16 November, 1970. FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS WORLD HEALTH ORGANIZATION Rome, 1971 PARAQUAT IDENTITY Chemical name 1, 1'-Dimethyl-4,4'-bipyridylium ion 1, 1-Dimethyl-4,4'-bipyridirium Synonyms (Dichloride)-PP 148, Gramoxone, Preeglone, Weedol Di(methyl sulphate)-PP 910, Aerial Gramoxone Structural formulaOther relevant chemical properties Available as the di(methyl sulphate) or the dichloride which are white crystalline solids; the di(methyl sulphate) is deliquescent. The salts melt with decomposition in the region of 300°C. Both compounds are stable in acid or neutral solutions and unstable in alkaline solution, very soluble in water and decompose in ultraviolet light. They are inactivated by inert clays and by anionic surfactants. Solutions of paraquat become intensely purple on reduction, due to the formation of a water-soluble, relatively stable free radical. The reduction is autoxidizable, and solutions of the free radical absorb at 396 nm; the unreduced form absorbs at 256 nm. Vigorous reduction gives tetrahydro derivatives and ultimately the fully saturated base. The redox potential (-446 mV) is independent of pH. Concentrated aqueous solutions of paraquat corrode steel, tinplate, galvanized iron and aluminium. Purity Technical, 90-95 percent EVALUATION FOR ACCEPTABLE DAILY INTAKE BIOCHEMICAL ASPECTS Absorption distribution and excretion Paraquat is not readily absorbed from the gut (Daniel and Gage, 1966). Following oral administration, peak concentrations of paraquat in the blood are reached within one to six hours. Paraquat does not appear to be selectively concentrated by any tissues in the body (Conning et al., 1969). Paraquat (14C-methyl labelled) administered to rats by an oral or subcutaneous route was completely recovered in the excreta. Following oral administration of 4-6 mg/kg body-weight of paraquat as the dichloride salt, from 99-102 percent of the administered dose was recovered in urine (6 percent) and faeces (93-95 per cent). Following subcutaneous administration of 21-23 mg/kg body-weight (methyl sulphate salt) from 85-112 per cent of the administered dose was recovered in the urine and faeces, (in urine 73-96 percent and in faeces 14-16 percent). Paraquat appeared to be poorly absorbed from the gut. However, 30 percent of a dose of paraquat is present in rat faeces as metabolic products. It has been suggested that paraquat may be metabolized in vivo by microbial action within the gut. A small proportion of these breakdown products may be absorbed from the gut (Daniel and Gage, 1966). Effect on enzymes and other biochemical parameters Studies of the reaction of paraquat with liver cell preparation suggest that cyclic reduction and reoxidation of the molecule may be a primary mechanism in the effects noted. These effects include a slight increase in oxygen uptake by mitochondria (possibly due to poor penetration of the mitochondrial membrane), a stimulation of oxygen uptake with NADH or ß-hydroxy-butyrate (but not succinate) as a substrate in mitochondrial fragments inhibited with Amytal, and an increase of NADPH oxidase in microsomes. Free radicals can be produced from paraquat incubated anaerobically in the presence of NADPH and microsomes derived from rat liver. Purified lipoamide dehydrogenase from pig heart is able to reduce paraquat to the free radicals in the presence of NADPH. Paraquat also increased the respiration of the liver mitochondrial fragments. This action is attributed to the activity of flavo-protein dehydrogenases. The property paraquat has of undergoing cyclic reduction and oxidation suggests that it could interfere in electron-transport processes, diverting electrons from the system and reducing oxygen to water. The resting respiration of mitochondria was almost unaffected by paraquat, probably because of its inability to penetrate the mitochondrial membrane (Gage, 1968a). Increased peroxidation occurs after paraquat treatment in plants and has been shown to be associated with the peroxidation of microsomal phospholipids in animals. An examination of lung lipids from rats treated with paraquat revealed no diminution in the content of unsaturated fatty acids. Preparations of rat liver either treated with paraquat in vitro or taken from animals given paraquat in vivo, showed no evidence of direct effect on fatty acid synthesis. Analysis of lung lipids up to six days after poisoning with paraquat revealed no significant changes in the composition of lung phospholipids. Large doses of tocopheryl acetate, given to animals before but not after exposure to paraquat, affords some protection against its toxic effect (Conning et al., 1969). In vitro binding studies have shown paraquat to bind to nucleic acids and acidic mucopolysaccharides; the binding is lessened by moderate salt concentrations. Paraquat in not bound by plasma protein or tissue homogenates, but small amounts may be bound by macrophages. In this instance, binding occurs in the cytoplasmic fraction (Conning et al., 1969). Manktelow (1967), in an attempt to explain the specific action of paraquat on lung tissue, has proposed that it interferes with the production of lung surfactant. Studies on the effects of expectorants on pulmonary congestion in rats administered paraquat (ip, 10 and 20 mg/kg) confirmed this observation (Cambar and Aviado, 1970). Paraquat was found to increase pulmonary resistance and moisture content and to decrease pulmonary surfactant, pulmonary compliance and respiratory minute volume. None of the expectorants examined had an effect on all of the parameters investigated. TOXICOLOGICAL STUDIES Special studies on reproduction Rat Six groups of rats (ten males or ten females per group) were examined for reproduction and teratogenic effects of paraquat at 0, 30 and 100 ppm in the diet fed to the parent (F0) generation only. Paraquat at 100 ppm was fed to F0 males only (mated to control females),F0 females only (mated to control males) and F0 males and F0 females (mated to each other). The paraquat fed parental (F0) generation was mated and produced three litters while exposed to paraquat. The F1 and F2 generations were not directly exposed to paraquat. The long-term ingestion of paraquat did not influence growth or fertility of the treated rats or of their offspring (Griffiths et al., 1966). A single intraperitoneal injection to rats of paraquat (6.5 mg/kg body-weight) on day 6 of gestation induced a high incidence of costal cartilage malformation in the embryos. This defect was not noted when injections were given on days 7-14 of gestation. A dose of 13 mg/kg on days 6-14 of gestation did not give this defect, although in most cases the dose was abortifacient (Khera and Whitta, 1968). Special studies on acute toxicity of a metabolite (N-methylisonicotinic acid) The acute rat oral LD50 of an unneutralized solution of the metabolite N-methylisonicotinic acid is between 2000 and 5000 mg/kg body-weight (McElligott, 1966; Clark, 1965b). Neutralization of the solution depressed the toxicity further (McElligott, 1966). The acute rat ip LD50 of N-methylisonicotinic acid is approximately 500 mg/kg body-weight (Clark, 1965b). Two of three male rats survived intraperitoneal administration of 4000 mg/kg of neutralized N-methylisonicotinic acid methyl sulphate (McElligott, 1966). Special studies on subacute toxicity of metabolite (N-methylisonicotinic acid) Rat One group of rats (seven males and seven females) was given N-methylisonicotinic acid methyl sulphate by oral intubation for 21 days at a dose of 2 g/kg body-weight/day. Toxic effects were limited to salivation, piloerection and occasional flaccidity. No effects on blood chemistry and gross or microscopic pathology were observed (McElligott, 1966). Groups of rats (25 males and 25 females) were fed N-methylisonicotinic acid methyl sulphate in the diet at concentrations of 0, 0.5, 2.0 and 4.0 percent for 90 days. Weight gains were reduced at the 4 percent level in both males and females. Histopathological observations include degenerative tubules in testes and degenerate cells in the lumen of the tubules in the epididymus at the 4 percent level. No abnormal effects were observed in mortality, body-weight, food consumption, haematology and gross and microscopic pathology at the 2 percent level and below (Broadurst et al., 1966). Rabbit Three female rabbits treated dermally with N-methylisonicotinic acid methyl sulphate powder at six alternate 24-hour periods displayed mild desquamation but no systemic effects (McElligott, 1966). Acute toxicity LD50 levels of paraquat in different species are given in Table I. After administration of acutely toxic doses to rats, all animals displayed the same toxic signs; they appeared healthy for the first 24 hours, and then became subdued and lethargic; respiration became progressively more difficult, and signs of anoxia were evident after 3-4 days; deaths occurred from 2-14 days after administration and followed by inappetance and weight loss; lung congestion was evident with varying degrees of consolidation. The pattern of mortality after a single oral dose of paraquat indicates that there is a maximum death rate in 2-5 days, with some deaths occurring at 10-12 days. Animals dying in the second group had marked congestion of the lungs with an oedematous fluid in many of the alveoli and excess macrophages in others. Cellular proliferation around the bronchi and in the walls of the alveoli was marked, and large tracts of the pulmonary tissue contained a high proportion of mast cells, with consequent reduction in the air-containing cavities. TABLE I Acute toxicity of paraquat in different species LD50 (mg ion/kg Animal Route Salt Form body-weight) Reference Chicken oral chloride 262 Swan, 1959 Rat oral chloride 120-157 Swan, 1959 Clark, 1965a Rat oral methylsulfate 100-110 Gaines, 1969 Rat oral methylsulfate 127-141 Swan, 1959 Clark, 1965a Rat dermal methylsulfate 80-90 Gaines, 1969 Rat ip chloride 19 Clark, 1965a Rat ip methylsulfate 16 Clark, 1965a Rat sc methylsulfate 24 Swan, 1959 Rat (4 hr) chloride 6.4 mg/l Palazzolo et al., inhalation (LC50) 1964 Guinea Pig oral chloride 30 Swan, 1959 Rabbit oral methylsulfate 126 Swan, 1959 Rabbit dermal chloride 240 McElligott, 1965 Rabbit ip chloride 18.2 McElligott, 1965 Cat oral chloride 35 Swan, 1959 Sheep oral chloride 100 Walley, 1964 Cow oral chloride 50-75 Walley, 1964 In two tests, instillation of approximately 6-10 mg of paraquat (dichloride or dimethyl sulphate salts) into the conjunctival sac of rabbits resulted in temporary slight lachrymation and conjunctival congestion one to three days after dozing. No permanent damage was noted, although in some cases recovery was slow. (McElligott, 1965; Clerk et al., 1966; Swan, 1959). Short-term studies Rabbit Multiple percutaneous administration of paraquat to rabbits at doses from 2.8 to 116 mg/kg body-weight daily for 20 days resulted in no effects seen at 2.8 mg/kg/per day. At 7.3 mg/kg, all animals survived, but there was lung congestion with consolidation of the alveoli. Two of three animals dosed at 14.5 mg/kg died within 20 days. When the site of application was covered by an occlusive dressing, amounts as low as 2.8 mg/kg (1.6 mg cation kg) resulted in moist red skin with sloughing of the skin (McElligott, 1965). Multiple percutaneous non-occluded application of paraquat dichloride to five male and five female rabbits at doses of 0, 0.6, 1.5 and 3.0 mg/kg body-weight/day for 20 days resulted in one male death at 1.5 mg/kg at 26 days and one male death at 3 mg/kg at 14 days. Signs of inactivity, muscular weakness, lassitude, nasal discharge and salivation were evident at the highest dose after 5-6 days. Local skin reactions were evident at all doses, with recovery occurring only at the 0.6 mg/kg level. No adverse affects were noted with regard to body-weight or gross and microscopic examination of surviving animals. Microscopic examinations of the dead animals revealed significant lung damage (Palazzolo and Calandra, 1965). Dog Five groups of dogs (from two to four males and females per group) were fed paraquat in their diet for 26 to 27 months at doses of 0, 10, 50, 125 and 250 ppm. Dietary feeding of paraquat dichloride at 250 ppm over a two month period resulted in body-weight depression, depressed food intake respiratory distress and death, with gross and histopathologic changes in the heart, kidneys, brain and lung. At 125 ppm over a 27-month period, the following signs were evident: death; depressed food intake body-weight; respiratory distress; and growths and microscopic changes in the lungs. Changes in organ-weights and decrease weights of spleen, brain and testes. Organ to body-weight ratio increases were noted with liver, heart, brain, thyroid and adrenal gland, while the spleen to body-weight ratio was decreased. No effects were noted at 50 ppm (34 ppm of paraquat ion) (Cervenka et al., 1964). One group of dogs (three males and three females) were fed paraquat dichloride 75 ppm in the diet for two years. Slight alterations were seen in the lungs upon gross and microscopic examination which were believed to be due to paraquat. No adverse effects were noted on body-weight, food consumption, survival, behaviour, haematological studies, blood chemistry, urinalysis, liver function tests, organ-weights and ratios and growths and microscopic examination of tissues other than lungs. The level of paraquat dichloride causing no toxicological effect on the dog was 50 ppm (34 ppm paraquat cation) (Baran and Calandra, 1965). Grazing animals Multiple daily oral administration to sheep at 20 mg/kg body-weight for five days resulted in death of all animals within two weeks. Multiple daily oral administration at 10 mg/kg for five days killed one of six sheep in 26 days, while 5 mg/kg for fourteen days resulted in listless animals; recovery was very slow (Walley, 1964). Multiple daily oral administration to cattle of 20 mg/kg body-weight for four days resulted in death within one week. Levels of 10 and 5 mg/kg body-weight orally for five and fourteen days, respectively, resulted in no deaths, but animals were listless and unhealthy; recovery was slow (Walley, 1964). Five groups of two sheep each and three groups of one calf each were exposed for four weeks to levels of 0, 1, 5, 10 or 20 ppm and 0.5 or 20 ppm of paraquat, respectively, in their drinking water. No adverse toxicological effects wore noted after one month (Sarfaty, 1963). Cattle suffered no toxic effects over a four-week period when grazed on pasture immediately after it had been sprayed with paraquat. Horses showed definite ill effects, including local lesions of the mouth and increased mucus secretions (Calderbank et al., 1968). Ewe lambs were grazed in pastures 30 days after treatment with 1-2 pounds of paraquat per acre with no effect on their growth or general well being (Torell and Kay, 1964). Subacute inhalation studies One group of dogs (one male and one female), guinea pigs (five males and five females) and rats (five males and five females) were exposed to an aerosol of paraquat dichloride at a concentration of 0.1 mg/1, six hours per day, five days per week, for three weeks. Growth depression was evident among the guinea pigs and rats, and the female dog lost weight. No effects wore noted with regard to untoward behavioural reaction, haematology, blood chemistry and gross or microscopic alterations of tissues (Palazzolo et al., 1965). Repeated daily 6-hour exposures to rats of paraquat aerosols over a three-week period produced signs of lung irritation, but no deaths, at 0.4 mg/l (Gage, 1968b). Long-term studies Rat Four groups of rats (30 males and 30 females, 60 of each sex were controls) were fed diets containing paraquat dichloride at levels of 0, 50, 125 and 250 ppm for two years. No adverse effects were seen at any level tested on growth, survival, behaviour, tumour incidence, haematologic studies, urinalysis, organ weights, ratios of organ to brain or organ to body-weight and gross pathologic examination. Microscopic examination of tissues and organs at 0 and 250 ppm (170 ppm of paraquat cation) revealed no adverse effects (Kohn at al., 1964). OBSERVATIONS IN MAN The hazard of paraquat to man has been associated with two general areas: accidental ingestion and dermal contamination. Accidental oral ingestion of paraquat in small quantities in man has generally resulted in death (sometimes delayed). In almost all cases where death occurred severe lung damage with proliferation of the alveolar walls was evident. These lesions were occasionally accompanied by renal failure as evidenced at autopsy by gross damage to the kidneys (Bullivant, 1966; Fennelly et al., 1968; Goulding, 1968; Campbell, 1968; Duffy and O'Sullivan, 1968; Tilling, 1968; Matthew et al., 1968 and Cowie and Kahn, 1968). In two accidental poisoning cases, recovery was complete (McKean, 1968; Lloyd, 1969). One suicide case from subcutaneous injection of paraquat resulted in delayed death in 17 to 18 days, with severe proliferation of the epithelium of the lung. Renal macroscopic or microscopic pathological changes were not evident (Almog and Tal, 1967; Herczeg and Reit, 1968). Dermal contamination had been shown to result in damage and discolouration of the fingernails. The damage included softening of the nail at the base, with occasional loss of the nail. It appeared that the damage was local because of the asymmetry of the lesion and because the toenails were not affected (Samman and Johnston, 1969). Following accidental instillation of paraquat into the eye, symptoms of irritation and inflammation of the conjunctiva increase and large areas of the conjunctiva and cornea may be shed. With treatment, recovery is slow (Calderbank, 1968; Cant and Lewis, 1968). COMMENT Paraquat is not readily absorbed from the gastrointestinal tract. After oral administration, it is excreted primarily in the faeces. After subcutaneous administration, it is primarily excreted in urine. The metabolic products formed by micro-organisms in the gut appear to be more readily absorbed than paraquat. No information is available on the toxicity of these metabolites formed by the gut flora. The soil metabolite N-methylisonicotinic acid is of a low order of toxicity as compared with the parent compound when tested in rats. From the available experimental data on animals and clinical experiences with man, it is evident that paraquat causes irreversible proliferative changes in lung tissue. The level of 75 ppm when fed to dogs over a two-year interval may be considered as a threshold dose on the basis of this pulmonary effect. An adverse effect on a long-term study in rats could not be demonstrated with levels up to 250 ppm. These results indicate that the rat is an insensitive species and, while the dog in affected by paraquat, its susceptibility may be lower than man. Man must be considered more sensitive than other species thus far examined. In man, the delayed occurrence of lesions in the lung, renal failure and a local effect on corneal epithelium, nasal mucosa, skin and fingernails suggest that paraquat my be considered a pesticide whose handling be restricted to trained professional personnel. In addition, studies on prophylaxis and treatment of the toxic effects of paraquat were considered to be urgently needed; reproduction studies are limited to one species, the rat. For the above-mentioned reasons, the Committee considered that it was possible to establish a temporary acceptably daily intake for man, based upon the no-effect level in the dog. TOXICOLOGICAL EVALUATION Level causing no toxicological effect Rat: 250 ppm in the diet, equivalent to 12.5 mg/kg body-weight/day (corresponds to 9.1 mg paraquat ion/mg body-weight/day) Dog: 50 ppm in the diet, equivalent to 1.25 mg/kg body-weight/day (corresponds to 0.91 mg paraquat ion/kg body-weight/day) ESTIMATE OF TEMPORARY ACCEPTABLE DAILY INTAKE IN MAN 0-0.001 mg/kg body-weight as paraquat dichloride (0-0.0007 mg/kg body-weight expressed as paraquat ion) RESIDUES IN FOOD AND THEIR EVALUATION USE PATTERN Herbicide and desiccant; rapidly absorbed by green plants but inactivated on contact with soil. Widely used for pre-crop and post-crop-emergence weed control, plantation weed control, aquatic weed control, pasture renovation, pre-harvest desiccation of hops, cotton defoliation and potato haulm and sugar cane desiccation. FATE OF RESIDUES In animals The fate of 14C-paraquat administered orally to cattle was investigated by Stevens and Watley (1966). They found that the bulk of radioactivity was excreted in the faeces and amounts <5% were present, largely as breakdown products, in the urine. A group of three cows, orally treated with a single dose of paraquat at 8 mg/kg, excreted between 0.003 and 0.008 percent of the dose in the milk and 0.24 percent of the dose in the urine within the seven-day testing interval (Stevens et al.,1966; Stevens et al., 1964). The amount of ingested material in the milk was the same irrespective of position of a radioactive label indicating that paraquat itself or a metabolite(s) containing methyl groups and intact ring structures was present. Two calves grazed for three or seven days on pasture containing residues of 300-400 ppm paraquat were found to have significant residues of paraquat only in the gut and stomach tissues. The kidney contained the highest tissue residues of 0.15 ppm, with traces found in lungs, heart and liver (Litchfield, 1969). In plants From observations made with 14C-labelled material, paraquat is transported to a slightly greater extent than diquat from the leaves of potato plants to the tubers (Slade and Bell, 1966). Coates et al. (1966) found appreciable movement in wheat, even in the roots. Slade (1966) studied the degradation of labelled paraquat on tomato, broad beans and maize plants; the degradation was found to be non-enzymic, but could be attributed to sunlight. Using potato plants, experiments showed that even if metabolism had occurred in the plant, no degradation products were transported to the tubers. In soil Paraquat has been shown to be degraded by soil microorganisms (Funderburk and Bozarth, 1967) to demethylated paraquat (1-methyl-4,4'-dipyridinium ion) and another compound characterized as the 1-methyl-4-carboxy-pyridinium ion (N-methylisonicotinic acid). The following degradation pathway by bacteria - demethylation of parent molecule and ring cleavage of one of the heterocyclic rings to eventually forms the carboxylated N-methyl-pyridinium ion.
In sunlight On the plant surface (and in solution), paraquat is rapidly broken down photochemically. The two end products from ultraviolet irradiation of solutions, both of which have very low toxicities in mammals, are identified as N-methyl betaines of iso-nicotinic acid and methylamine. Slade (1965, 1966) investigated the degradation of paraquat by both sunlight and the ultraviolet light from a mercury vapour lamp. Two degradation products were identified, 1-methyl-4-carboxypyridinium ion and methylamine hydrochloride; the following degradation pathway was proposed:
In water Paraquat applied to water for aquatic weed control purposes quickly disappears due to uptake by weeds and absorption by soil, silt and particulate suspended matter (Calderbank, 1968). No information is available on the ultimate fate of the chemical in this environment. The rate of disappearance in very variable, depending on the movement of the water and the presence of mud or suspended matter, but treatments within the range of 1-4 mg/litre in the water have resulted in only 0.1 mg/litre or less of paraquat being detectable in from 6 to 14 days after application. Decomposition of the killed weed is rapid, any remaining residue of paraquat thus liberated being subsequently absorbed on the bottom mud. Such residues in the largely organic muds may be more readily available to bacterial degradation than when absorbed to clay minerals in soils. Evidence of residues in food in commerce or at consumption Only when the crop in sprayed directly are significant residues of paraquat likely to be found. A summary of residues found in cotton after use for desiccation purposes is given in Table II. (Calderbank, 1968) TABLE II Paraquat residues in, ten days after desiccation at 0.5 lb paraquat/acre (U.S.A. results) Fraction analysed Paraquat found, ppm Cotton as picked, including trash and bolls 2.0 Ginned seed 0.18 Acid-delinted seed 0.05 Mechanically reginned seed 0.08 Lint cotton 3.0 Hulls 0.13 Trash 3.7 Crude oil Non-detected Meal 0.02 Data obtained following use of paraquat as a desiccant on several food crops has also been published (Calderbank, 1968); a summary of these results is given in Table III. METHODS OF RESIDUE ANALYSIS An ion-exchange method for determining paraquat residues has been developed by Calderbank and Yuen (1965). The method depends on the measurement of light absorption at 396 nm of reduced solutions of paraquat after concentration and purification by cation-exchange chromatography and has been used for a wide variety of food crops, water, etc.; limit of sensitivity is 0.01 ppm. Radaelli and Bosetto (1968) used it for the determination of residues in clays and mineral soils. Paraquat and its photochemical decomposition product, 4-carboxyl-1-methyl pyridinium chloride, can be determined polarographically (Slade and Jackson, 1971). TABLE III Summary of paraquat residues in food crops, desiccation uses Rate of Average Residues Application Paraquat Crop (lb/acre) (ppm) Barley 0.5 -1.0 3-10 Wheat 0.5 -1.0 1-2.5 Maize 0.5 -1.2 ND2/0.2 Rice (with husk) 0.15 -0.54 0.7-22 Rice (dehusked or polished) 0.15 -0.54 ND-0.2 Peas, beans, sunflower seed 0.35 -1.2 ND-2.0 Sorghum seed 0.25 -1.0 0.1-0.4 Cotton (as picked) 0.5 -1.0 2-3 Onions 0.5 -2.0 0.05 -0.5 Potatoes 0.5 -1.5 0.02 -0.13 Sugar cane juice 0.5 -2.0 ND Seed oils (sesame, sunflower, rape, cotton) up to 1.2 ND 1/ 3-21 days after application 2/ ND = none detected The lesser duckweed (Lemna minor L) provides a simple sensitive bioassay technique for determining paraquat residues in water (Funderburk and Lawrence, 1963). Plant extracts containing paraquat have been chromatographed on thin layers of silica gel by Slade (1966) using 5 M ammonium chloride solution for development. Faust and Hunter (1965) determined paraquat in natural surface water at 256 nm following chemical clean-up by ion exchange. NATIONAL TOLERANCES Country Crop Tolerance (ppm) U.S.A. Potatoes 0.5 Apples, pears, apricots, avocados, bananas, cherries, citrus fruits, figs, grapes, papayas, peaches, 0.05 nectarines, plums, prunes (fresh) maize, lettuce, melons, peppers, tomatoes 0.05 maize and sorghum grain 0.05 maize, sorghum and soybean forage 0.05 Almond hulls 0.5 Almonds, filberts, macadamia 0.05 nuts and walnuts Coffee beans, olives, soybeans 0.05 Cottonseed 0.5 Sugarbeet (roots and tops) 0.5 Information has also been received regarding - Cotton (as picked) 2 mg/kg APPRAISAL Paraquat is very widely used for weed control in many crops, as an aquatic herbicide and as a desiccant on cotton, potato haulm and sugar cane. Paraquat in a stable compound in plants. Ultraviolet light, sunlight and soil micro-organisms degraded paraquat to N-methyl-isonicotinic acid and methylamine hydrochloride. Following ingestion by cows, traces of paraquat or its metabolites are secreted into the milk. Residues are very unlikely to accrue from soil or pre-emergence applications but can occur following use for desiccation purposes. The suggested tolerances are based on each desiccation usage. The colorimetric procedure of Calderbank and Yuen (1965) should be suitable for regulatory purposes. RECOMMENDATIONS FOR TOLERANCES, TEMPORARY TOLERANCES OR PRACTICAL RESIDUE LIMITS TEMPORARY TOLERANCES (effective to June 1974) Cottonseed 0.2 ppm Potatoes 0.1 ppm Cottonseed meal 0.05 ppm Cottonseed oil (edible) 0.05 ppm Sugar cane juice 0.05 ppm FURTHER WORK OR INFORMATION REQUIRED (before June 1973) 1. Detailed comparative toxicity and metabolism studies in order to elucidate the reason for the comparatively high sensitivity of man to this compound. 2. Additional reproduction studies on at least one species. 3. Examination in several species of the toxic effects of metabolites formed by the action of the gut flora. DESIRABLE Long-term oral studies on additional species. REFERENCES Almog, C.H. and Tal, E. (1967) Death from paraquat after subcutaneous injection. Brit. Med. J., 3: 721 Baran, J. and Calandra, J.C. (1965) Two-year chronic oral toxicity of paraquat-beagle dogs. Unpublished report from Industrial Bio-Test (Aug. 1964) to ICI through Chevron Chemical Co. to FDA Broadhurst, T.O., Griffiths, D. and McElligott, T.F. (1966) Ninety-day oral toxicity of N-methyl-isonicotinic acid methosulfate - albino rats. Unpublished report IHR/194 (April 1966) ICI Ltd. through Chevron Chemical Co. to FDA Bullivant, C.M. (1966) Accidental poisoning by paraquat: report of two cases in man. Brit. Med. J., 1: 1272-1273 Calderbank, A. and Yuen, S.H. (1965) An Ion-exchange method for determining paraquat residues in food crops. Analyst, 90: 99-106 Calderbank, A., McKenna, R.M., Stevens, M.A. and Walley, J.K. (1968) Grazing trials on paraquat-treated pasture. J. Sci. Fd. Agric. 19: 246-250 Calderbank, A. (1968) The bipyridylium herbicides. Effects on man, Advances in pest control research, Metcalf R.L. Ed. vol 8, p. 224 Interscience Publishers N.Y. Cambar, P.J. and Aviado, D.M. (1970) Bronchopulmonary effects of paraquat and expectorants. Arch. environm. Hlth, 20: 488-494 Campbell, S. (1968) Paraquat poisoning. Clinical Toxicol.,1: 245-249 Cant, J.S. and Lewis, D.R.H. (1968) Ocular damage due to paraquat and diquat. Brit. Med. J., 2: 224 Cervenka, H., Kay, J.H. and Calandra, J.C. (1964) Chronic oral toxicity of paraquat - beagle dogs. Unpublished report from Industrial Bio-Test (Aug. 1964) to ICI through Chevron Chemical Co. to FDA Clark, D.G. (1965a) The acute toxicity of paraquat. Unpublished report IHR/170 (Jan. 1965) from ICI through Chevron Chemical Co. to FDA Clark, D.G. (1965b) Unpublished report TR/438 (25 Jan. 1965) from ICI Ltd. through Chevron Chemical Co. to FDA Clark, D.G., McElligott, T.F. and Hurst, E.W. (1966) The toxicity of paraquat. Brit. J. Indust. Med., 23: 26-32 Coates, G.E., Funderburk, H.H., Lawrence, J.M. and Davis, D.E. (1966) Factors affecting persistence and inactivation of diquat and paraquat. Weed Res.,6:58-66 Conning, D.M., Fletcher, K. and Swan, A.A.B. (1969) Paraquat and related bipyridyls. Brit. Med. Bull.,25:245-249 Cowie, J. and Kahn, J. (1968) Acute renal failure in case of paraquat poisoning. Brit. Med. J., 1: 749-750 Daniel, J.W. and Gage, J.C. (1966) Absorption and excretion of diquat and paraquat in rats. Brit. J. Industr. Med.,23: 133-136 Duffy, B.S. and O'Sullivan, D.J. (1968) Paraquat poisoning. J. Irish Med. Assoc.,61: 97-98 Faust, S.D. and Hunter, N.E. (1965) Chemical methods for the determination of aquatic herbicides. J. Am. Water Works Assoc., 57: 1028-1037 Fennelley, J.J., Gallagher, J.T. and Carroll, R.J. (1968) Paraquat poisoning in a pregnant woman. Brit. Med. J.,3: 722-723 Funderburk, H.H. and Lawrence, J.M. (1963) A sensitive method for determination of low concentrations of diquat and paraquat. Nature, 199: 1011-1012 Funderburk, H.H. and Bozarth, G.A. (1967) Review of the metabolism and decomposition of diquat and paraquat. J. Agric. Fd. Chem.,15: 563-567 Gage, J.C. (1968a) The action of paraquat and diquat on the respiration of liver cell fractions. Biochem. J.,109: 757-761 Gage, J.C. (1968b) Toxicity of paraquat and diquat aerosols generated by a size selective cyclone. Effect of particle size distribution. Brit. J. Industr. Med.,25: 304-314 Gaines, T.B. (1969) Acute toxicity of pesticides. Toxicol. Appl. Pharmacol.,14: 515-534 Goulding, R. (1968) Paraquat poisoning. The Practitioner,200:739-740 Griffiths, D., Ponsford, D.C. and Hurst, E.W. (1966) A study of reproduction in rats treated with paraquat in the diet. Unpublished report IHR/185 (Jan. 1966) from ICI Ltd. Herczeg, E. and Reit, A. (1968) Lungenveranderunger bei todlich verlaufener paraquatvergiftung. Zbl. allg. Path. Anat., 111: 325-328 Khera, L.S. and Whitta, L.L. (1968) Embryopathic effects of diquat and paraquat in the rat. Ind. Med. Surg., 37: 553 Kohn, F.E., Kay, J.H. and Calandra, J.C. (1964) Two-year chronic oral toxicity of paraquat-albino rats. Unpublished report from Industrial Bio-Test Laboratories (July 1964) to ICI through Chevron Chemical Co. to FDA Litchfield, M.H. (1969) Grazing trial on paraquat-treated pasture. Unpublished report IHR/257 (April 1969) ICI Ltd. Lloyd, E.L. (1969) Recovery after taking Weedol. Brit. Med. J., 2: 189 Manktelow, B.W. (1967) The loss of pulmonary surfactant in paraquat poisoning. Brit. J. Exptl. Path. 48: 366-369 Matthew, H., Logan, A., Woodrugg, M.F.A. and Heard, B, (1968) Paraquat poisoning - lung transplantation. Brit. Med. J.,3: 759-763 McElligott, T.F. (1965) The dermal toxicity of paraquat. Unpublished ICI report IHR/172 (Jan 1965; through Chevron Chemical Co. to FDA McElligott, T.F. (1966) Toxicological report - N-methyl isonicotinic acid methosulphate. Unpublished report TR/512 (April 1966) ICI Ltd. through Chevron Chemical Co. to FDA McKean, W.I. (1968) Recovery from paraquat poisoning. Brit. Med. J.,3:292 Palazzolo, R.J., Kay, J.H. and Calandra, J.C. (1964) Acute aerosol inhalation toxicity of paraquat dichloride. Unpublished report from Bio-Test Lab. Inc. to ICI (15 April 1964) through Chevron Chemical Co. to FDA Palazzolo, R.J. and Calandra, J.C. (1965) Sub-acute dermal toxicity of paraquat dichloride. Unpublished report by Industrial Bio-Test Lab. (Aug. 1966) through California Chemical Co. to FDA Palazzolo, R.J., Kay, J.H. and Calandra, J.C. (1965) Sub-acute aerosol inhalation toxicity of paraquat dichloride. Unpublished report from Indus. Bio-Test Lab. (Jan. 1965) to ICI Ltd. through Chevron Chemical Co. to FDA Radaelli, L. and Bosetto, M. (1968) Determination of paraquat in clays and mineral soils. Ricerca Scient., 38: 855-857 Samman, P.D. and Johnston, E.N.M. (1969) Nail damage associated with handling of paraquat and diquat. Brit. Med. J., 1: 818-819 Sarfaty, A.B. (1963) Observational trials on toxicity to sheep and cattle. Unpublished report Chevron Chemical Co. to FDA Slade, P. (1965) Photochemical degradation of paraquat. Nature, 207: 515-516 Slade, P. (1966) The fate of paraquat applied to plants. Weed Res., 6: 158-167 Slade, P. and Bell, E.G. (1966) Movement of paraquat in plants. Weed Res., 6: 267-274 Slade, P. and Jackson, L.S. (1971) Pestic. Sci., in preparation Stevens, M.A., Walker, G.H. and Walley, J.K. (1964) The excretion of 14C paraquat by the cow. Unpublished report IHR/164 (Oct. 1964) by ICI through Chevron Chemical Co. to FDA Stevens, M.A. and Walley, J.K. (1966) Tissue and milk residues arising from the ingestion of single doses of diquat and paraquat by cattle. J. Sci. Food Agric., 17: 472-475 Swan, A.A.B. (1959) Unpublished report by ICI TR/241 (Dec. 1959) submitted through Chevron Chemical Co. to FDA Tilling, W. (1968) Paraquat - intoxikation. Dtsch. Medizin. Wchschr.,50: 2439-2441 Torell, D. and Kay, B.L. (1964) Pasturing of sheep on paraquat treated forage. Unpublished report - 383-42 Chevron Chemical Co. to FDA Walley, J.K. (1964) Paraquat toxicity in sheep and cattle. Unpublished report IHR/166 (April 1964) submitted from ICI through Chevron Chemical Co. to FDA
See Also: Toxicological Abbreviations Paraquat (HSG 51, 1991) Paraquat (PIM 399) Paraquat (JMPR Evaluations 2003 Part II Toxicological) Paraquat (WHO Pesticide Residues Series 2) Paraquat (Pesticide residues in food: 1976 evaluations) Paraquat (Pesticide residues in food: 1978 evaluations) Paraquat (Pesticide residues in food: 1981 evaluations) Paraquat (Pesticide residues in food: 1982 evaluations) Paraquat (Pesticide residues in food: 1986 evaluations Part II Toxicology)