EPD does not routinely gather data for Total PCB biota contamination in Hong Kong as only data pertaining to sediment contamination is gathered. Some data are, however, available from other studies and these have been compared with the data obtained during this baseline Study. It should be noted that major problems in comparing PCB data between studies occur due to the number of PCB congeners in existence (209) as well as the need for information relating to the total lipid content of samples (see Section 4.1.3)(64) . For example, this baseline Study measured Total PCB, whereas, other studies such as that conducted for the SSDS trawling surveys analysed commercially important fish and crustacean species for individual PCB congeners(65) . For these reasons, data may not be entirely comparable.

The highest Total PCB concentrations in tissues recorded in this baseline Study were 25.0 ug kg-1 (wet weight) from Mantis Shrimp (see Section 4.3.2). In the SSDS Study Mantis Shrimps (Oratosquilla nepa) contained PCB 28 (a PCB congener) concentrations of < 25.0 to < 76 ug kg-1 (wet weight) (66). Highest PCB 28 concentrations recorded in Oratosquilla nepa were from station S03 which is located to the west of Tsing Yi. Cotton Prawn (Metapenaeus joyneri) also accumulated high PCB 28 body burdens and the highest values recorded ranged from < 36.0 ug kg-1 in station S02 (located north of Lantau) and < 72.0 ug kg-1 (wet weight) at station S06 (near station WS1 south of Tsing Yi).

The highest concentrations of Total PCB recorded by Phillips (1985) during a previous study, that represented the first of its kind in Hong Kong, of bivalve tissues from locations around Hong Kong recorded values of 1696.0 ug kg-1 (dry weight) from Causeway Bay and 1904.0 ug kg-1 (dry weight) from Rennies Mill(67). These values are considerably higher than recorded in either this baseline Study or the SSDS survey. The apparent disparity between the results of the three studies may be explained by the fact that bivalves are known to accumulate many contaminants to extremely high concentrations (as they lack many of the enzymes required to metabolise certain contaminants), different instrumental analyses were used, analyses were conducted on both wet and dry tissue, and organisms may have large differences in lipid content.

PCBs have been recorded at high levels in cetacean blubber from Hong Kong waters. Parsons reported Total PCBs in older cetaceans at concentrations greater than 50.0 ug kg-1 and a high body burden of 62.8 ug kg-1 was recorded in blubber from one individual(68). In the most recently published data available, Minh et al, reported Total PCBs in Hong Kong dolphin and porpoise blubber at 3.3 to 50.0 ug kg-1 and 0.8 to 48.0 ug kg-1 (wet weight) for Sousa chinensis and Nephocaeana phocaenoides, respectively(69). These concentrations are considerably higher (an order of magnitude) than found in Mantis Shrimp in this baseline Study. This is not surprising, however, as cetaceans are at the top of their food chain, contain significant fat deposits (blubber) and Total PCBs are known to undergo biomagnification. Total PCB tissue concentrations higher than 50.0 ug kg-1 are thought to pose a serious threat to the health of higher organisms such as mammals and the levels recorded in the blubber of local cetacean species are a cause for concern.

It is important to note that recorded Total PCB levels may not directly reflect the organic contaminant concentration of Hong Kong waters, however, since cetaceans and their prey (which will be the main source of Total PCB to cetaceans) can have wide geographic ranges and tissue burdens may include contributions from conditions elsewhere.

Table 4.3a presents a summary of the values of Total PCB levels recorded amongst different groups of marine organisms. The organisms represent different components of the marine ecosystem, including the filter feeding mussel Perna viridis, the predatory mantis shrimp Oratosquilla nepa and Hong Kong's resident species of marine mammal Sousa chinensis and Neophocaena phocaenoides.

Note:
1 Phillips (1985)
2 Mouchel (1996)
3 Minh et al (1999)
a Dry weight
b Wet weight