Separation and aquatic toxicity of enantiomers of the organophosphorus insecticide O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN).

Enantioselectivity in separation and toxicity of chiral pesticides has become important research areas in environmental science, because these studies give a deeper insight into the environmental effect of chiral pesticides. In this study, enantiomeric separation of the organophosphorus pesticide and acaricide O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN) was investigated by chiral high-performance liquid chromatography (HPLC) with two chiral stationary phases. The racemate and separated enantiomers of EPN were tested for aquatic toxicities assay using Daphnia magna and zebrafish (Danio rerio) embryo test. The enantiomers of EPN were completely separated on Chiralpak AD and Chiralpak AS columns coupled with a circular dichroism detector at 236 nm. Better separations were achieved with lower temperatures (e.g., 20°C) and lower levels of polar modifiers (e.g., 1%). A significant difference was found between the enantiomers in their acute aquatic toxicity; the (+)-enantiomer was about 10 times more toxic than its antipode. On the contrary, the (-)-enantiomer induced crooked body, yolk sac edema and pericardial edema significantly more than (+)-enantiomer in the zebrafish embryo test. These results suggest that biological toxicity of chiral pesticides should be assessed by using their individual enantiomers with more comprehensive methods.