Research Product

Acute, lethal effects of fenthion (an organophosphate insecticide) on mysids (Mysidopsis bahia), grass shrimp (Palaemonetes pugio), pink shrimp (Penaeus duorarum), and sheepshead minnows (Cyprinodon variegatus) were determined in laboratory tests and after field applications. Exposure at four field sites ranged from short-term exposures (12 h or less) of rapidly decreasing fenthion concentrations to extended intervals (more than 72 h) with slowly increasing or decreasing fenthion concentrations. Laboratory-derived LC50s provided a reliable benchmark for predicting acute, lethal effects of fenthion on caged animals in the field when exposures persisted for 24 h or more but overestimated the toxicity for exposures less than 24 h. Laboratory pulse-exposure tests with rapidly changing concentrations for 12 h were predictive of nonlethal and lethal effects observed for short-term field exposures.