Degradation of the insecticide SD 8280, 2-chloro-1-(2, 4-dichlorophenyl)vinyl dimethyl phosphate,in soils

The degradation of the insecticide SD 8280 2-chloro-1-(2,4-dichlorophenyl)vinyl dimethyl phosphate] in soil has been examined under laboratory conditions using two soils from rice-growing areas in Japan and one UK soil. In all soils SD 8280 underwent degradation to 1-(2,4-dichlorophenyl)ethanol, 2,4-dichlorobenzoic acid, 2-chloro-1-(2,4-dichlorophenyl)vinyl methyl hydrogen phosphate and 2′,4′-dichloro-acetophenone. These degradation products were present in the soils as free (extractable) compounds and as bound forms and soil binding occurred most extensively with 2,4-dichlorobenzoic acid. Polar products were also formed and these appeared to be in part the result of complexing of degradation products with the soil organic matter. The effect on the degradation of the insecticide of varying the moisture content of one soil was also examined. In soil incubated at 11, 17, 30 and 62% moisture the recovery of SD 8280 after 60 days was 71.0, 12.3, 9.0 and 11.3%, respectively. Although the rate of degradation varied, the same degradation products were detected in all samples.