Laboratory studies on mechanisms for the degradation of aldicarb, aldicarb sulfoxide and aldicarb sulfone

Abstract

Abstract Experiments were performed in order to better define the degradation mechanisms and kinetics for aldicarb and its two metabolites, aldicarb sulfoxide and aldicarb sulfone. The mechanisms studied were oxidation in surface soil and saturated zone soil samples, degradation in saturated zone soil samples and distilled water hydrolysis. The studies showed that soil is an important mechanistic factor, probably because surface catalysis occurs. Temperature and pH are important factors in determining degradation rates. The experiments seem to indicate that microbial oxidation is an important degradation mechanism in the surface soil, but the breakdown of aldicarb residues to noncarbamates is largely the result of chemical hydrolysis. The reduction of aldicarb sulfoxide to aldicarb was observed in the presence of limestone but only after an incubation period of two to six months. No reduction of aldicarb sulfone to aldicarb sulfoxide was observed in these experiments. The complexity of degradation is such that laboratory studies can augment but not replace well-designed experiments conducted under actual field conditions.