Evaluates the risks to human health and the environment posed by trichlorfon, a broad-spectrum organophosphorus insecticide which acts as a "slow release" source of dichlorvos in the mammalian body. Marketed since the 1950s, trichlorfon is used to protect field and fruit crops, to control forest insects, and to control internal and external parasites in domestic and farm animals. Trichlorfon, formulated as metrifonate, has also been used for the pharmacological treatment of Schistosoma haematobium in millions of patients. The compound is under investigation as a treatment for Alzheimer's disease.

A review of environmental levels and human exposure concentrates on the significance of residues detected in crops, the milk of treated cows, and other food items as possible sources of exposure for the general public. Noting that detected levels are far below the established acceptable daily intake, the report concludes that trichlorfon does not constitute a health hazard for the general population. Concerning effects on environmental organisms, the report cites evidence that trichlorfon is moderately toxic for fish and birds, and moderately to highly toxic for aquatic arthropods, supporting the conclusion that this insecticide should never be sprayed over water bodies or streams.

The remaining sections evaluate data from toxicity studies in laboratory animals and in vitro test systems, from several hundred case reports of accidental or intentional human poisoning, and from studies of schistosomiasis patients treated with metrifonate. Though poisoning may have serious effects, including delayed neurotoxicity, the report concludes that, when good work practices and safety precautions are followed, trichlorfon is unlikely to present a hazard for occupationally exposed workers. The report further notes that, in the millions of schistosomiasis patients treated with metrifo-nate, reported side effects have been mild and rare.

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