Fate of malathion and O,O,S-trimethyl phosphorothioate by-product in Hawaiian soil and water

The fate of malathion and O,O,S-trimethyl phosphorothioate in soil and water during a fruit-fly eradication experiment was studied using samples from Kauai, Hawaii. Malathion showed rapid degradation in laboratory soil microcosms and in the field. The degradation products were dimethyl phosphorodithioic acid and diethyl fumarate. Degradation of O,O,S-trimethyl phosphorothioate in soil microcosms was fairly slow. The principal process in the degradation of malathion in various waters was an elimination reaction, though photolysis and biodegradation played minor roles. Dissipation of O,O,S-trimethyl phosphorothioate in river water took place mainly by biodegradation. The sorption of both insecticides to soils and the potential for groundwater contamination are also considered.