Parathion tolerance

Residues in many foods should decrease because EPA has canceled many of the food crop uses of methyl parathion, including fruits and vegetables commonly eaten by children, some other vegetable uses, some feed uses, and all nonfood uses such as ornamental plants and nursery stock uses. Tolerances for methyl parathion on these foods and feed also have been canceled. This action was taken because of a concern for risks to children and workers. Some food and feed uses and tolerances are to be maintained. 

EPA. 2001. Methyl parathion notice of pesticide tolerance revocations final rule. Department of Health and Human Services. U.S. Environmental Protection Agency. 40 CFR Part 180. Federal Register 66(4) 1242-1246. 

Pesticide residues consist of chemicals that might occur in a commodity as a result of application of a pesticide. Such chemicals typically correspond to compounds for which a regulatory agency has or will set a tolerance, i.e., a maximum residue limit, specific to the commodity. In either a field study or a market basket survey, residues to be determined will be those which result from application of the specific pesticide that the study is intended to support. A market basket survey, however, might be intended to support not just one but several different pesticides of the same or different chemical classes. In addition, a market basket survey might include pesticides not used in the USA but for which import tolerances exist. For example, some uses of the parathion family of pesticides on food products have been abandoned in the USA but remain in other countries that export the products to the USA. A market basket survey offers a means to evaluate actual dietary exposures to residues of such pesticides. In addition, tolerance expressions frequently include multiple compounds, all of which must typically be determined in residue field trials. The sponsor of the market basket survey must decide whether to analyze for all compounds in the applicable tolerance expression or to restrict the program to selected analytes, such as the active ingredient. 

The Food and Drug Administration has not as yet held hearings concerning the establishment of formal tolerances for DDT or parathion on fresh produce or in processed foods. For apples and pears, an informal tolerance for DDT of 7 p.p.m. has been announced (3). [These hearings were in progress at the time of publication. ]... 

Begun in 1944 with DDT and in 1947 with parathion, the present report includes analytical data secured from certain chemical, mechanical, and solvent actions on apples, pears, lemons, and oranges. In the absence of established tolerances for these two insecticidal materials, it is hardly possible to interpret the significance of many of these data with respect to consumer hazard. 

Cross-tolerance between disulfoton and another organophosphate, chlorpyrifos, was observed in mice (Costa and Murphy 1983b). Because of this cross-tolerance, a benefit is derived as a result of this interaction. In the same study, propoxur-tolerant mice were tolerant to disulfoton but not vice versa. Propoxur (a carbamate) is metabolized by carboxylesterases, and these enzymes are inhibited in disulfoton-tolerant animals disulfoton-tolerant animals are more susceptible to propoxur and/or carbamate insecticides than are nonpretreated animals. In another study, disulfoton-tolerant rats were tolerant to the cholinergic effects of octamethyl pyrophosphoramide (OMPA) but not parathion (McPhillips 1969a, 1969b). The authors were unable to explain why the insecticides OMPA and parathion caused different effects. 

In 1954, Congress enacted the Miller Amendment to the Federal Food, Drug, and Cosmetic Act (FFDCA), which required that a maximum acceptable level (tolerance) be established for pesticide residues in foods and animal feed (for example, 10.0 ppm carbaryl in lettuce, or 1.0 ppm ethyl parathion on string beans). In 1958, congress enacted the Food Additives Amendment to FFDCA, which regulated pesticide residues in processed foods. 

Other types of inhibitors may not be so tolerable. Organophosphorus compounds, used in nerve gases and weed killers (e.g., parathion), form a covalent irreversible bond with the active serine and permanently inactivate acetylcholinesterase. This is a type of suicide inhibition because the inhibitor reacts with the enzyme much like a substrate, but becomes blocked in the intermediate state where the enzyme-phosphoryl bond is stable, in contrast to the hydrolyzable enzyme-acetyl bond. These compounds are life-threatening. 

During the last decade parathion has been the most used organo-phosphorus insecticide. It has been proved to be valuable in crop protection 27). However, using this compound so much has also resulted in numerous accidental intoxications, and many have been lethal 28). In aquatic environments parathion hydrolyzes to yield p-nitro-phenol or oxidizes to yield paraoxon (25, 26). Baker (29) has shown that substituted phenols aflFect the odor quality of drinking water. p-Nitrophenol may be chlorinated at a water treatment plant to produce an odorous product. The U. S. Public Health Service has adopted 1 /xg/liter as a limit for phenolic compounds in water (10). Paraoxon is more toxic to insects and mammals than the parent compound parathion (27). The lethal dose (LD50) for male white rats is 14 mg/kg for parathion while that determined for paraoxon is only 3 mg/kg (30). Bioassay studies with fathead minnows indicated a Median Tolerance Limit (TLni) (96 hours) for parathion of 1.4 mg/liter and 0.3 mg/liter for paraoxon. 

At that time public attention was particularly becoming concerned about the application of chemicals such as the very toxic parathion to crops used for human food. Public Law 83-518, known as the Miller Bill, which introduced the conception of tolerance (or permitted) levels of residues in foods, had been issued in the USA in 1954 and the authorities in various other countries had introduced or were drafting legislation on similar lines. 

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