CARBAMATE INSECTICIDES - REMOVAL FROM WATER BY CHLORINATION AND OZONATION

A simple approach for removal of carbamates from drinking water by disinfection is presented. Four carbamates, aldicarb, methomyl, carbaryl and propoxur were reacted with excess of each of three disinfectants, Cl2, ClO2 and O3. Carbaryl and propoxur did not react with chlorine, none of the selected carbamates reacted with ClO2, and all reacted very rapidly with O3. The reaction kinetics were determined for aldicarb and Cl2 and for methomyl and Cl2. Product analysis for the reaction of aldicarb and Cl2 was carried out using reverse-phase HPLC and GC-MS. The common degradation products, aldicarb-sulfoxide and aldicarb-sulfone were found together with other by-products. A mechanism is suggested based upon an electrophilic ionic attack by hypochlorous acid. A possible mechanism of electrophilic attack by ozone is also suggested. A preliminary bioassay using Daphnia magna, to compare the toxicity of aldicarb and chlorination by-products of aldicarb showed that the by-products were less toxic. Therefore, removal/degradation of these carbamates can be achieved using Cl2 and/or O3 but not ClO2. © 1990.