Vertical fluxes and accumulation of organochlorine pesticides in sediments of Haihe River, Tianjin, China.

Organochlorine pesticides (OCPs) concentrations in sediments and sediment trap fluxes of particulate organic carbon and OCPs were measured from October 2006 to May 2008 in the urban reach of Haihe River, Tianjin, China, in order to investigate vertical fluxes and accumulation of OCPs in sediments. The concentrations of OCPs in sediments (dry weight basis) were in the range of 2.08-10.07 ng/g (mean 4.70 ng/g) for HCHs (alpha-, beta-, gamma-, delta-HCH), 5.82-43.39 ng/g (mean 17.43 ng/g) for DDTs (p,p'-DDE, p,p'-DDD, o,p'-DDT, p,p'-DDT). Compared with data reported in Haihe River 2003, the levels of OCPs showed a significant decrease between 2003 and 2008. This is mainly attributed to significant decrease of production and usage of HCHs and DDTs and biodegradation of HCHs and DDTs in sediment. Concentrations of HCHs and DDTs in sediments were well correlated with sediment organic carbon contents. Concentrations of OCPs in settling particles (dry weight basis) ranged from 21.2 to 138.4 ng/g (mean 52.6 ng/g) for HCHs, 30.0-245.7 ng/g (mean 87.1 ng/g) for DDTs, which were 2.2-48.2-fold higher than those associated with sediments. beta-HCH was the dominant HCH isomer in both sediments and settling particles. Among DDTs, p,p'-DDE was found to be dominant in sediments, while p,p'-DDT was the predominant form in settling particles. This suggests that further biodegradation of OCPs occurred during the course of sedimentation and burial. The annual sediment trap flux of OCPs in Haihe River in the urban area of Tianjin was 177-211 microg/m(2) yr for HCHs and 213-341 microg/m(2) yr for DDTs, respectively.