Abstract

Blubber samples from eight Indo-Pacific hump-backed dolphins (Sousa chinensis) and eleven finless porpoises (Neophocaena phocaenoides) stranded between 1993 and 1996, in Hong Kong waters, were collected for organochlorine analysis. Levels of total PCB were low (0.19 μg·g-1 to 125 μg·g-1 in S. chinensis and 0.47 to 17 .3 μg·g-1 in N. phocaenoides) and are similar to those typically recorded from other cetaceans. PCB concentrations in calves (<1 year old) were generally half those of the adults. PCBs were also detected in a sample of milk extracted from the stomach of a calf. The concentrations of PCB in this sample were similar to those in the blubber sample of the calf itself (2.49 μg·g-1 vs 2.32 μg·g-1). Profiles of the major PCB congeners were similar between the two species. Levels of chlorinated benzene, hexachlorocyclohexanes, dieldrin, chlordane and mirex were low, generally below 1 μg ·g-1 lipid. Total DDT levels, however, were quite high. The median level of total DDT was 26.7 μg·g-1 for S. chinensis and 50.3 μg·g-1 for N. phocaenoides. The relatively low DOE/DDT ratios suggest that there may have been relatively recent releases of DDT into the marine environment. The relatively high DDT levels may be a cause of concern regarding the health of the animals. The high neonatal mortality rate observed in Hong Kong's cetaceans may partly be attributed to their compromised immune functions due to organochlorine exposure. Further studies are required to identify the effects of organochlorine exposure on the resident cetacean populations in Hong Kong.