Concentrations, enantiomeric compositions, and sources of HCH, DDT and chlordane in soils from the Pearl River Delta, South China

Abstract

Concentrations, and enantiomeric compositions of HCH, DDT and chlordane in 74 soils of the Pearl River Delta, South China were investigated. The mean concentrations of HCHs and DDTs descended in the order: crop soils>paddy soils>natural soils. The concentrations (ng/g dw) of p,p'-DDE, p,p'-DDT, p,p'-DDD and o,p'-DDT in crop soils were 0.14-231, 0.07-315, <DL-96.7 and 0.06-73.8, respectively, while those of chlordane were generally below 0.78 for trans-chlordane (TC) and 0.75 for cis-chlordane (CC). Enantiomeric factors (EF value) were determined for o,p'-DDT, alpha-HCH, TC and CC. Both preferential depletions of (-) enantiomer and (+) enantiomer were observed for o,p'-DDT and alpha-HCH, indicated by EF values either <0.5 or >0.5. An EF value >0.5 generally suggested a preferential degradation of the (-) enantiomers of both TC and CC. The racemic alpha-HCH observed in the soils with higher HCH concentrations indicated that the transformation from gamma-HCH (e.g. lindane) to alpha-HCH may be an important process in the soils. The isomer ratios of p,p'-DDT/(DDE+DDD), o,p'-DDT/p,p'-DDT and enantiomeric compositions of o,p'-DDT suggested that both illegal use of technical DDT and the DDT impurity in dicofol may be responsible for the freshly DDT input in the region. The sources of DDTs were drawn by principal component analysis-multiple linear regression (PCA-MLR). The relative contributions of dicofol-type DDT, residues, and fresh technical DDT were estimated to be 55%, 21% and 17%, respectively. In addition, CC was found to degraded faster than TC in soils from the Pearl River Delta. The study demonstrated that the combination of isomer ratios and enantiomeric composition analysis may provide critical information on the potential sources and fate of organochlorine pesticides in soil.