Spatial and temporal variations of organochlorine pesticides (OCPs) in water and sediments from Honghu Lake, China

Honghu Lake in Jianghan Plain, central China is an important habitat for many migratory birds and an important site for freshwater fishery, and Honghu Lake region is also a main area for rice and cotton production in China. To understand the status and changes of organochlorine pesticide (OCP) contamination, and to assess the OCPs' risks for the ecosystem in Honghu Lake, thirty surface water samples, fifteen surface sediments, and a sediment core were collected in January and July, 2005. OCPs, such as DDTs, HCHs and chlordanes, were determined by GC-ECD in all samples. Concentrations of OCPs in surface water collected during the wet season (July 2005) were relatively higher than those collected during the dry season (January 2005), indicating that the increasing land runoff during the summer might bring the chemical residues from soils to Honghu Lake. The relatively low α-HCH/γ-HCH ratio and the relatively high o,p'-DDT/. p,p'-DDT ratio indicated the application of lindane on regional agricultural lands in late spring and summer (April-August), which increased the increasing contribution of dicofol to DDT in Honghu Lake, respectively. The levels of σHCHs and σDDTs in the surface sediments were relatively lower than those from the Yangtze River Delta, but comparable to those from other lakes and rivers in China. The composition of HCHs and DDTs in the surface sediments showed that there was fresh input of lindane (γ-HCH), and DDT residues in Honghu Lake were aged and probably mainly originated from weathered agricultural soils of surrounding Jianghan Plain. Wash out of HCHs and DDTs from soil was the possible process which caused the increasing concentrations of these chemicals in recent years