Occurrence, sources and ecotoxicological risks of polychlorinated biphenyls (PCBs) in sediment cores from urban, rural and reclamation-affected rivers of the Pearl River Delta, China.

Sediment cores were collected to a depth of 40 cm (50 cm for urban river sediments) in the Pearl River Delta of China from rural river sediments and river sediments undergoing the process of urbanization and reclamation. Polychlorinated biphenyls (PCBs) in sediment cores were determined to evaluate their levels, distribution, possible sources and potential risks aimed at providing effective information of management practices for local governments. Our results showed that the total concentrations of PCBs (∑16PCBs) in urban, rural and reclamation-affected river sediments ranged from 16.15 to 477.85 μg kg (dry weight), with mean values of 121.94, 150.49 and 124.20 μg kg (dry weight), respectively. The most abundant PCB congeners among the study area were light PCBs. Generally, PCBs showed a decreasing trend with depth along sediment cores at most sampling sites. Source analysis indicated that PCBs in the three types of river sediments mainly originated from Aroclor 1242, 1248, 1254 and 1016. Risks evaluation based on sediment quality guideline quotient (SQGQ) showed PCBs at most sampling sites would cause no or moderate adverse biological effects on benthic organisms except surface sediments of U4 and R5 (high adverse biological effects). However, threshold effects level (TEL) is ignored when calculating SQGQ, which might underestimate the risks of PCBs. Thus, a new SQGQ (NSQGQ) taken TEL into consideration was established. Results showed that NSQGQ could evaluate ecotoxicological risks of PCBs better. Redundancy analysis (RDA) showed that PCBs in sediments were positively correlated with sand content and microbial biomass carbon (MBC) (p < 0.05).