Ten organophosphate (OP) pesticides: phorate, disulfoton, terbufos, methidathion, bensulide, chlorethoxyfos, phosmet, methyl parathion, phostebupirim, and temephos were evaluated for their potential to undergo oxidation to their respective oxons and/or other oxidation analogues in laboratory water. Samples were collected at time intervals up to 72h of chlorination and analyzed by both gas chromatography-mass selective detection (GC-MSD) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results show that methidathion and methyl parathion were stable in unchlorinated water, while all other OP pesticides were not stable over the 72h exposure period. In chlorinated water, phorate and disulfoton formed stable sulfone oxons. Temephos formed stable dioxon sulfoxide and dioxon sulfone. Methidathion, bensulide, chlorethyoxyfos, methyl parathion, and phostebupirim formed stable oxons over the 72h exposure period. Terbufos, phorate, disulfoton and temephos oxon sulfoxides; temephos sulfoxide; and phosmet oxon were initially formed but were not detected after 24h. The data illustrate that organothiophosphate pesticides may form oxons and/or other oxidation analogues during chlorination in water treatment plants, which are persistent for at least 72h.
