Methyl parathion

Abstract

Evaluates the risks to human health and the environment posed by methyl parathion, a highly toxic organophosphorus ester insecticide. Close to 600 studies were critically assessed. Introduced as a commercial chemical in 1949, methyl parathion is used as a contact insecticide and acaricide for the protection of cotton, soybeans, cereals, tobacco, peanuts, vegetables, citrus fruits, and other crops. The compound is applied as a foliar spray by aircraft or ground equipment. Because methyl parathion is a non-selective pesticide that kills beneficial species as well as pests, a section devoted to effects on environmental organisms concentrates on several studies documenting high toxicity for honey bees. These studies also show that incidents of bee kills were more severe with this insecticide than with others, underscoring the need to time spraying operations with extreme care. The report concludes that methyl parathion should never be sprayed under windy conditions, and that overspraying of water bodies must be avoided. The most extensive section evaluates studies of toxic effects observed in experimental animals and in vitro test systems. The report found no evidence of carcinogenicity associated with long-term exposure, and no evidence that this insecticide acts as a primary eye or skin irritant. The final section evaluates effects on humans, drawing on a number of case reports of accidental and sometimes fatal poisoning. The report concludes that the only confirmed effects on humans are the signs and symptoms characteristic of systemic poisoning by cholinesterase-inhibiting organophosphorus compounds. No cases of organophosphorus-induced, delayed peripheral neuropathy have been reported. Concerning risks to workers, the report concludes that, with good work practices, hygienic measures, and safety precautions, methyl parathion is unlikely to present a hazard for occupationally exposed workers