Ecological risk assessment of polychlorinated biphenyl contamination in the Mai Po Marshes Nature Reserve, Hong Kong

The main objective of the present study was to investigate polychlorinated biphenyl (PCB) contamination in Mai Po Marshes Natural Reserve, Hong Kong. During June-December 1997, samples of sediments and aquatic organisms including fish (Oreochromis mossambica x O. nilotica, Mugil cephalus) and shrimps (Metapenaeus ensis, Macrobrachium nipponense), were collected from gei wais and total PCB levels were measured. The concentrations of PCBs in sediments reduced gradually from coastal sites (8.13 ng g^-1 dry wt) to landward sites (1.47 ng g^-1 dry wt), which suggested that PCBs in Deep Bay waters were the main input source entering the reserve. The calculated PCB concentrations in water were generally safe for aquaculture according to the U.S. EPA guidelines, but PCBs in muscle tissues of grey mullet (Mugil cephahus) exceeded the guidelines. PCB concentrations (ng g^-1 lipid) in tilapia increased with increases in fish body size, which was possibly due to active uptake of PCBs by tilapia. Within the same shrimp species, different sized organisms showed similar PCB contents in lipid, indicating that lipid content rather than body size determined body concentrations. The PCB concentrations in the aquatic organisms in the reserve posed no hazards to birds according to predicted egg toxicity effects. The estimated BSAFs (biota-sediment accumulation factors) obtained in the present study ranged from 1.10 to 2.37, which were similar to the reported value of 2.10 derived from various aquatic biota species.