Characteristics and risk assessment of PCBs in drinking water source reservoirs of the Zhoushan Islands, East China

Water, sediment, and surrounding soil samples from 3 drinking water source reservoirs, Cengang Reservoir (CGR), Hongqiao Reservoir (HQR), and Chengbei Reservoir (CBR) in the Zhoushan Islands (eastern coastal area of China), were collected and analyzed for 14 polychlorinated biphenyls (PCBs) to understand their levels, distributions, and possible sources. Concentrations of Sigma(14)PCBs in water from the 3 reservoirs ranged from 0.79 to 21.00 ng/L (average 10.31 ng/L), and those in sediments and surrounding soil were within the ranges of 9.09-614.90 ng/g (dry weight) and 2.44-41.13 ng/g, with averages of 211.58 and 15.83 ng/g, respectively. The Sigma(14)PCBs concentrations in water at CGR and CBR water intakes slightly exceeded the US Environmental Protection Agency standard for freshwater; the probability of toxic risk of PCBs in sediments of CBR was >50%. The lower molecular weight (tri- to penta-) PCBs (72.4-99.9% of Sigma(14)PCBs) were the dominant PCB congeners at almost all sites. The PCBs in the 3 reservoirs probably originated from a shared pollution source through atmospheric deposition of Aroclor 1242, an industrial PCB source historically used in this region. Based on the contamination of the 3 reservoirs and the potential sources, we recommend the elimination of possible point-source pollution relative to PCBs within the CBR watershed, and the dredging of surface sediment in the CBR. In addition, engineering measures such as green buffer zones could be constructed around the reservoirs to reduce the PCB pollutants from land runoff, especially around the east and north boundaries of CBR.