Concentrations of PCBs in coastal mangrove sediments of Hong Kong

The concentrations of polychlorinated biphenyls (PCBs) in surface sediments of ten mangrove sites in Hong Kong were determined by Congener-specific and Arcolor methods. Spatial variations were found between mangrove sites and within the same site, indicating that the sediment samples were heterogeneous and total PCBs concentrations in mangrove sediments should be normalised to compensate for natural variability and for identifying serious anthropogenic contamination. In addition to total organic carbon, Al, Fe and Mn were possible normalisers. Based on PCB/normaliser ratio and 95% prediction limits of scatter plots between total PCB and normaliser, all mangrove sites were not seriously contaminated by human activities. The estimated total PCBs concentrations (quantified by Congener-specific method) for most sediment ranged from 0.5 to 5.8 ng g−1 (dry weight, n=92). However, very high concentrations of PCB were found in sub-samples from Yi O, Tolo Pond and Lai Chi Wo, suggesting that these samples represented the PCB contaminated “hot spots”.