Biota

There are few data available on Total DDT concentrations of tissues from Hong Kong marine species. Direct comparisons with other studies are difficult owing to inherent species-specific differences in lipid content (organochlorines are mostly sequestered in the lipid layers and hence difference in lipid content between organisms will potentially confound the analyses), seasonal differences in lipid content (lower lipid levels following spawning or reproduction) and analytical techniques employed. Total DDT was recorded in biota tissues from the majority of stations monitored (Table 3.4a and Table 3.4b).

In a pioneering study of Total DDT contamination of marine biota in Hong Kong, Phillips (1985) recorded concentrations in bivalves (Perna viridis) at levels ranging from 256 - 2043 ug kg-1 (dry weight)(40). These values are not directly comparable to this baseline Study, however, as dry tissues were analysed. The highest Total DDT concentrations were mainly from bivalves collected in Victoria Harbour. Highest concentrations of Total DDT in the present baseline Study were recorded from the pelagic fish, Gizzard Shad (Clupanodon thrissa) where concentrations of 21.7 to 56.2 ug kg-1 were evident. Mantis Shrimp (Oratosquilla interrupta) and crabs (Charybdis affinis) also contained high Total DDT levels and were recorded at 20.0 and 19.6 ug kg-1, respectively.

As part of the ongoing SSDS study, Total DDT was recorded in commercial fisheries species(41). The SSDS study revealed high Total DDT concentrations in certain commercial fish and crustacean species. The Mantis Shrimp (Oratosquilla oratoria) trawled from stations at S01 (west of NS4 near Urmston Road), S04 (south of WS1 south of Tsing Yi), S03 (west of WS1), S02 (northwest Lantau) and S06 (southeast of WS1) had Total DDT concentrations of 90.4, < 77.0, < 86.0, 238.3 and 239.4 ug kg-1, respectively. The Total DDT levels in Mantis Shrimp represent the highest recorded in the species during the SSDS study and are considerably higher than concentrations determined in this baseline Survey. The SSDS trawl survey data showed that other Mantis Shrimps (Oratosquilla nepa) also contained high Total DDT concentrations. Mantis Shrimp (O. nepa) trawled from stations S05 (Southeast of WS1), S03, S02, S01 and S06 had total DDT ranging from 50.5 to < 304.0 ug kg-1 (wet weight). Cotton Prawn (Metapenaeus joyneri) trawled during the SSDS survey had Total DDT ranging from < 126.0 to < 144.0 ug kg-1 (wet weight). These values far exceed Total DDT values recorded in this baseline survey where Cotton Prawn from Southern Waters contained only 1.18 ug kg-1 (wet weight).

The SSDS fish survey data revealed that higher Total DDT levels were recorded in the Threadfin Bream (Nemipterus sp.) when compared to this baseline survey. Stations S01, S02, S03 and S05 had Total DDT in the range of 53.0 - 244.8 ug kg-1 (wet weight). SSDS data showed that the Lionhead Collichthys lucidus (from stations S01, S02 and S03) also contained high Total DDT and upper values ranged from 61.3 - 77.3 ug kg-1 (wet weight). These concentrations in fish tissues are higher than reported for Gizzard Shad in this baseline survey.

Total DDT has been recorded in both the blubber and milk of Hong Kong cetaceans and was found at concentrations as high as 20.6 ug kg-1 which are some of the highest concentrations recorded for small cetaceans(42). In the most recent published report pertaining to Total DDT in local cetaceans, Minh et al (1999) recorded DDT in the blubber of Sousa chinensis ranging from 5.1 to 80.0 ug kg-1 (wet weight), and in the finless porpoise (Neophocaena phocaenoides) from 2.6 to 160.0 ug kg-1 (wet weight)(43) . Owing to the Total DDT to DDE ratio, these authors suggested that inputs to Hong Kong coastal waters are still occurring. These values are an order of magnitude higher than those recorded in Gizzard Shad in this baseline Study (21.7 to 56.2 ug kg-1) though blubber is known to accumulate Total DDT to exceptionally high concentrations. The Total DDT recorded values from different species in other studies are summarised in Table 4.1a.

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