Seasonal and spatial distributions and possible sources of polychlorinated biphenyls in surface sediments of Yangtze Estuary, China

Abstract

The surface sediment samples taken from 30 sites of the Yangtze Estuary in both the flood and dry seasons were analyzed to reveal the spatial and seasonal distributions of polychlorinated biphenyls (PCBs). Samples collected in the flood season showed higher PCB concentrations, larger PCB fluctuations and higher portions of large grain sediments in the inner estuary area compared with those collected in the dry season, indicating significant seasonal variations of PCBs. The effects of the physicochemical characteristics (TOC and grain size) of surface sediments on the distributions of PCBs were also investigated. Masked by various other factors, the TOC contents and sediment grain sizes did not exhibit a strong influence on the distributions of PCBs. Analysis of the PCB homolog and congener distribution patterns revealed a predominant proportion of light PCBs with 2–3 chlorines. According to the PCB homolog profiles and principal component analysis (PCA) of source contributions, non-point sources including atmospheric deposition and surface runoff associated with stormwater were suggested to be the major sources of PCBs in the surface sediments of the Yangtze Estuary.