Impacts of channel morphology on residues and ecological risks of polychlorinated biphenyls in water and sediment in Chahe River

The impacts of channel morphology on the residues and ecological risks of 14 polychlorinated biphenyl (PCB) congeners in water and sediment were investigated in summer (July) and autumn (September) in the Chahe River, in Nanjing, China. The residual concentrations of tri-chlorobiphenyls (tri-CBs, PCB 18) and tetra-CBs (PCB 52) in water were significantly higher than those of penta-CBs to deca-CBs, and the average residual concentration of ∑PCBs (sum of 14 PCB congeners) in summer was about six times higher than in autumn. However, the residues in sediment did not change significantly. Redundancy analysis (RDA) indicated that channel morphology and the corresponding environmental indices had significant impacts on PCB residues and their composition profiles in water and sediment. The overflow weir and lake-type watercourse may remarkably reduce the residual concentration and ecological risks of PCBs in water. The highest reduction percentages of the residual concentration and ecological risks of ∑PCBs induced by an overflow weir were 78% and 67%, respectively, and those induced by a lake-type watercourse were 36% and 70%, respectively. The watercourses with different channel morphologies were ranked by residual ∑PCBs concentrations in the following descending order: the natural ecological watercourse, vertical concrete watercourse, and vegetation-type riprap watercourse. However, they were ranked by residual ∑PCBs concentrations in sediment in the following descending order: the vertical concrete watercourse, vegetation-type riprap watercourse, and natural ecological watercourse.