Total DDT is a globally distributed persistent organochlorine pesticide. In the marine environment, DDT is persistent and has a tendency towards bioconcentration and biomagnification. DDT toxicity is temperature-dependent. At higher temperatures (eg 37oC) DDT is not particularly toxic, but, at lower temperatures is highly toxic and hence to the majority of cold-blooded aquatic organisms. Metabolism of DDT is slow and it tends to accumulate to high concentrations in organisms fatty tissue. DDT is nevertheless thought to remain biologically active in body fats of higher organisms and can interfere with fertility and reproductive success. DDT thus has the potential to directly affect Darwinian fitness. DDT is not a registered pesticide in Hong Kong and has been banned for use since 1988 though it may still be in use in Mainland China(24) . From 1979 to 1982, however, between 5,023 and 5,996 kg of DDT pesticide was imported into Hong Kong annually(25) and owing to high persistence, DDT and its derivatives may still be found locally.

Total DDT concentrations in sediments analysed in this baseline Study were frequently above the ISQV-Low exceedance value (ie 1.58 mg kg-1 ) and hence potentially harmful to benthic organisms. Sediment re-suspension may also provide a DDT exposure pathway to pelagic (ie water column) organisms.