As mentioned above, the majority of samples collected for DDT analysis recorded values above the detection limit in both wet and dry seasons (Table 3.4a and 3.4b). Highest concentrations were recorded in specimens of the Gizzard Shad (Clupanodon thrissa) collected from Deep Bay (Figure 3.4a). This fish is a pelagic species reported to feed on detrital organic matter, benthic algae and bivalves(20)). In December 1998, mean DDT values were recorded at 56.2 ug kg-1 with lower values recorded in January (21.7 ug kg-1). All of the other marine species collected during the dry season recorded mean values of less than 15 ug kg-1.

During the wet season (August 1999), Total DDT concentrations were recorded at the highest levels in the Mantis shrimp (Oratosquilla interrupta) and swimming crab (Charybdis affinis) collected from Deep Bay. Mantis shrimps from this locality had mean Total DDT of 20.0 ug kg-1 whereas the crabs contained levels of 19.6 ug kg-1. The mantis shrimp is a burrowing species and consequently is in close proximity to DDT scavenged by sediments. The swimming crab, however, feeds on prawns and fish it encounters at the sediment surface.

Various species were sampled for tissue analysis in the different sampling areas, although the concentrations of DDT were recorded at the highest levels from biota collected in Deep Bay (DB - Figure 3.4a). DDT levels for Mirs Bay, Port Shelter and Southern Waters biota did not exceed 10 ug kg-1 in any of the species sampled either in the wet or dry seasons.

An evaluation of the environmental significance of the Total DDT values recorded in these baseline surveys is hampered by a lack of comparable studies and also by variation in the target species analysed. Information gathered from these surveys has been compared with the limited data available from other surveys in Hong Kong including the EM&A programme for CMP IV(21)) and the SSDS Baseline Monitoring(22)) .