Focused toxicity identification evaluations to rapidly identify the cause of toxicity in environmental samples

Over the past 5 years numerous toxicity studies in California using the amphipod, Hyalella azteca, have reported that pyrethroid insecticides, and less frequently the organophosphate insecticide chlorpyrifos, have been responsible for observed toxicity. As work continues to characterize and mitigate these water quality impacts, an approach is needed to screen samples exhibiting toxicity quickly and cost-effectively to establish if these same substances are again responsible, or if other, more atypical toxicants are responsible. Causality is often determined by a standard toxicity identification evaluation (TIE), but when there is strong historical evidence of a likely toxicant, we propose use of a focused TIE procedure to screen samples using manipulations specifically designed to identify pyrethroid- or chlorpyrifos-related toxicity. The focused tests use reduced temperature, piperonyl butoxide addition, and engineered enzymes specifically designed to hydrolyze certain pyrethroid and organophosphate insecticides. The target compounds exhibit unique response profiles to this battery of manipulations, distinct from each other and other non-insecticides. When used in conjunction with analytical chemistry data, the focused approach was successful in identifying cause of toxicity in a variety of urban and agricultural settings.