PCBs are a group of organic chlorine compounds which are derived from biphenyl with some of the hydrogen atoms replaced by chloride. Because of their high stability and low aqueous solubility, PCBs are persistent in the environment. Urban stormwater runoff is considered as an important source of many pollutants, including PCBs, to aquatic environments. PCBs can cause endocrine disrupting effects, morphological deformities and neurobehavioral alterations. Many microorganisms have been reported to utilize and metabolize PCBs as carbon and/or energy sources under both aerobic and anaerobic conditions. Biofilm creates a favorable environment for the growth of microorganisms and increases the possibility of degradation of PCBs. In this study, affiliations of PCBs with stormwater sediment and their biodegradation by soil biofilms were studied. For all the sediment samples, the sediment fraction and the settleable fraction accounted for more than 99% of the total sediments (Figure 1). For site 2-entrance, the settleable fraction (~25 to 75 µm) tended to absorb three times more PCBs than the sediment fraction (＞75 µm ) (Figure 2). Additionally, PCBs extracted from the two fractions were mainly higher-chlorinated PCBs. This can be explained by the fact that less-chlorinated PCBs are more volatile and easy to be biodegraded or photolyzed. Besides, all of the four sites had bacteria in them (Figure 3) and sediment collected from site 3 had PCB-dechlorinating bacteria in it (Figure 4). These bacteria form soil biofilms to resist external environment and enhance the dechlorination of PCBs. In conclusion, PCB-dechlorinators exist in sediment from site 3 and they grow as biofilms on sediment particles to degrade PCBs. Sediment transport is an important removal pathway for PCBs in urban stormwater, especially for PCBs with more chlorines.

Occurrence of polychlorinated biphenyls (PCBs) in stormwater sediments and their dechlorination by soil biofilms

254th National Meeting (2017)

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