Polychlorinated biphenyls (PCBs) are a group of man-made structurally similar chemicals (congeners) that have been used as insulating fluids in the electricity industry (many of the transformers in Hong Kong were PCB-filled)(59) and as plasticisers. PCBs are highly volatile, are consequently transported in air and are now universally distributed(60). PCBs are toxic and have also been implicated in immunosuppression, reproductive failure and cancer(61). They were subsequently withdrawn from general use in many countries in the 1970's. PCBs are hydrophobic and thus accumulate predominantly in fatty tissues and are highly environmentally persistent as they are only slowly metabolised by oxidation.

Total PCBs in tissues obtained from the biota were recorded above detection limits at 45% of stations during December 1998, 30% in January, 52% of stations in August and 50% of stations in the September 1999 trawling. The high prevalence of Total PCBs recorded in local species is indicative of both environmental persistence and possibly continuing inputs (eg from illegal dumping of PCB contaminated wastes). For example, Morton (1989)(62) noted that in Hong Kong in the 1980's, over 3300 PCB-filled capacitors were either still in use or in storage.