Risk Assessment of Fenthion Oxide Derivatives in Aqueous Environment

Fenthion (MPP), an organophosphorus pesticide, is widely used as an agricultural and household insecticide. The oxons are known to be the actual toxic forms of organophosphorus pesticides. Using an in vitro cytochrome P450 (CYP) metabolism system, MPP was metabolized to produce five metabolites: MPP sulfoxide, MPP sulfone, MPP oxon, MPP oxon sulfoxide and MPP oxon sulfone. MPP sulfoxide was the main product, while MPP oxon sulfone and the other metabolites were produced in small amounts. On the other hand, MPP was converted to MPP oxon sulfone by chlorination in a water purification system, raising the possibility of human exposure to MPP oxon sulfone through drinking water. MPP oxon sulfone showed the highest acute toxicity among MPP and its metabolites. In addition, MPP oxon sulfone was not metabolized by CYP3A4, the major CYP isomer in humans. It is important that MPP and its oxides are monitored and their health risk assessed to control drinking water safety because MPP was detected in river water.