Bioconcentration of organophosphorus pesticides to hazardous levels by amphibians.

Organophosphorus pesticides have generally low persistence in the environment, but they may persist in water and accumulate in certain aquatic vertebrates. Frogs are resistant to cholinesterase inhibitors; thus it was suspected that they might accumulate the pesticides. Tadpoles concentrated pesticides from water up to 60 times; those exposed to 1 ppm parathion and 5 ppm fenthion were lethal when they were fed to mallard ducks. Dicrotophos, malathion, and acephate were not accumulated to levels such that they were lethal when consumed in a single meal by ducks. Brain cholinesterase levels were correlated with dose and effect. Metabolites of parathion and fenthion produced by the tadpoles were rapidly excreted and it was concluded that they play a small role in the toxicity of the larvae to ducks. Dangerous levels of some pesticides may be accumulated by amphibians in nature and may adversely affect carnivorous species.