Distributions and sources of polychlorinated biphenyls in the coastal East China Sea sediments.

The Yangtze River estuary (YRE) and the adjacent East China Sea (ECS) inner shelf is an important sink of pollutants originated from mainland China. In this work, we studied the spatial and temporal variations and sources of polychlorinated biphenyls (PCBs) in sediments from the YRE and the ECS inner shelf. Total concentration of 23 PCBs (Σ23PCB) ranged between 24.3 and 343.3 pg/g (with a mean value of 126.7 pg/g), and higher values occurred in the estuarine region. The homolog profile was dominated by 3-5Cl CBs, accounting for 76.1% of Σ23PCB. The Cl proportion ranged from 45.1% to 58.8% (with a mean value of 49.9%); the lowest level appeared in the estuarine region, and it increased with distance from the YRE. Lower chlorinated congeners were carried mainly by the YR into the ocean, to be finally buried in sediments of the estuary region and vicinity. However, higher chlorinated ones were imported mainly via direct emission from local sources, to be finally buried in sediments farther away from the estuary. Of the PCBs in surface sediments, 40.1% came from the YR, 37.9% from the local sources and the rest 22.0% from atmospheric deposition. In a sediment core, we found that 81% of PCBs were technically produced and 19% unintentionally produced in the last century. Before the 1970s, PCB levels were influenced predominantly by the production and consumption of technical PCBs. While in recent decades, the effect of human activities on PCB levels has been increasing continuously.