Historical Trends and Chiral Signatures of Organochlorine Pesticides in Sediments of Qiandao Lake, China.

This study investigated the enantiomeric and depth profiles of organochlorine pesticides (OCPs) accumulated in the sediments of Qiandao Lake, China. OCP concentrations in sediments have increased gradually since the early 1960s, when extensive OCPs application in China began. Concentrations reached maximum levels after 1992, this timing corresponds with the emerging of the "new" usage of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethane (DDTs). In addition, the degradation of chiral OCPs were enantioselective, resulting in enriched (-)-enantiomers for α-HCH and o, p'-DDD. However, both preferential depletions of (-) enantiomers and (+) enantiomers were observed for o, p'-DDT. This outcome was indicated by enantiomer fractions (EF) values either greater or less than 0.5.