Effects of Cd 2+ and Pb 2+ on enantioselective degradation behavior of α-cypermethrin in soils and their combined effect on activities of soil enzymes

Heavy metals may coexist with pesticides in farmland through wastewater irrigation, application of pesticides and chemical fertilizers, or unappropriated waste disposal. Heavy metals are toxic to soil microorganism, which may influence the environmental behavior of pesticides subsequently. In this study, the influence of Cd2+ and Pb2+ on the degradation of α-cypermethrin and its metabolites, 3-phenoxphenoxybenzoic acid (3-PBA) and 3-(2',2'-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (DCCA), were investigated through soil incubation experiment. It was found heavy metals like Cd2+ and Pb2+ will inhibit the degradation of α-cypermethrin, especially at high concentrations. Pb2+ has a stronger inhibitory effect on the degradation of α-cypermethrin than Cd2+ in the same concentration. With the presence of 10 mg/kg Pb2+, the half-life of α-cypermethrin increased from 41.1 to 99.9 days, even the half-life was 129.3 days with 50 mg/kg of Pb2+. Besides, heavy metals influenced the chiral selective degradation of α-cypermethrin. The enantiomer fraction was near 0.5 when 10 mg/kg of heavy metals existed. Furthermore, the adverse effects of heavy metals on soil urease, catalase, and sucrase activity were assayed. In tested concentrations (10 and 50 mg kg-1), the heavy metals result in strong inhibition of the activity of the enzymes present on soil, jeopardizing the biodegradation by the microbiome and which may inhibit the degradation of α-cypermethrin.