The vertical distribution, sources and ecological risks of residual organochlorine pesticides in sediments of the North China's largest freshwater lake

Inland freshwater is an essential resource for human survival and development; however, the occurrence of organochlorine pesticides (OCPs) in the largest freshwater lake in northern China remains largely unknown. Among the 24 OCPs detected in the lake sediments, hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) were predominant compounds. The most abundant isomers were β-HCH and p,p'-DDT, reflecting their extensive use in agriculture and aquaculture. The Fuhe River, a critical channel for agricultural irrigation and domestic sewage, was identified as the primary pathway for transporting OCPs from upstream sources into Baiyang Lake. The residual OCPs in surface sediments were higher than those in deeper sediments, indicating the recent input of lindane, dicofol and dieldrin. Especially, the α-HCH/γ-HCH ratios (0–1.8) in the sediment cores, indicated a mixed historical input of both lindane and technical HCHs. The o,p'-DDT/p,p'-DDT > 0.5 in the bottom sediments were attributed to the earlier use of technical DDT. Notably, the DDTs in the upstream section of the Fuhe River, with high ERM values, posed a significant ecological risk, whereas the levels of DDD, DDE, and chlordane in the sediments were below the ERL values, indicating low potential ecological risks. The sediment assessment indicated potential ecological risks from HCHs and dieldrin in the residential areas. In contrast, the sediment-associated surface water posed no significant carcinogenic or non-carcinogenic risks to humans.