Enhanced Reduction of Extractable Polychlorinated Biphenyls and Toxicity in Sediment by Organic Matter

Regional serious contamination of polychlorinated biphenyls (PCBs) is threatening the local residents and ecosystem. PCBs are often very stable, but the extractable portion which is mainly responsible for their risk in sediment might be decreasing due to biodegradation and formation of non-extractable residues. In the present study, the natural reduction of extractable PCBs in regional contaminated sediments during a period of 5 years was investigated. Besides, influences of sediment organic matter on the reduction of extractable PCBs and the toxicity were studied by incubating sediments spiked with PCBs and humic acid for 5 years. The loss percentage of extractable PCBs reached 40.3%, 46.9%, 63.5%, and 70.1%, respectively in sediments at site B, C, D, and E of Nanguan River during 5 years. The sediment organic matter content was significantly correlated with the loss percentage of total PCBs (p < 0.05) and higher chlorinated PCBs (p < 0.01). In incubated sediments, significant reduction of extractable PCBs and toxicity was observed at the end of the fifth year (p < 0.05). Addition of humic acid promoted the reduction of extractable PCBs and toxicity in sediment. These results will help us to better understand the risk caused by PCBs in regional contaminated sediments over time and also provide us a possible method to enhance the reduction of extractable PCBs in contaminated sediments.