Marine sediments have a much greater potential to accumulate pollutants than marine water due to their higher organic material content and thus greater contaminant binding properties. Therefore, contaminant levels in marine sediments can have a major influence on contamination of marine waters (through dissolution of weakly bound contaminants over time), marine organisms (through ingestion and uptake as a result of benthic feeding activities) and humans (through consumption of seafood which has ingested marine sediments). Information on the quality of marine sediments in Hong Kong from EPD's regular monitoring programme, which involves sampling at 62 stations throughout the WCZs, is reviewed in more detail in Annex F2. In summary, sediments with high levels of nutrients have been identified at stations in the Tolo Harbour, Port Shelter and Deep Bay WCZs, in parts of Mirs Bay and throughout Victoria Harbour. Sediments with elevated heavy metals concentrations occur in areas of Tolo Harbour, inner Deep Bay and Victoria Harbour and trace organic-contaminated sediments have been found in parts of the Southern, Deep Bay and Junk Bay WCZs and throughout Victoria Harbour.

ARoutine monitoring of sediments for an expanded list of parameters is also carried out by EPD in a number of typhoon shelters in Hong Kong. Sediments are generally more contaminated in typhoon shelters than in surrounding waters. Particularly anaerobic conditions were detected in sediments from typhoon shelters in Victoria Harbour (particularly Causeway Bay, To Kwa Wan, Kwun Tong, Aldrich Bay and Sam Ka Tsuen) and the Rambler Channel. Significant heavy metal contamination has also been found in the Kwun Tong and Rambler Channel Typhoon Shelters in the last five years and the highest PCB levels were also found at Kwun Tong.

The EPD's routine monitoring programme monitors some major toxic organic compounds in sediments but does not include DDT (a pesticide) and tributyltin (TBT - an antifoulant). Although some information on organic contaminants is available for dredging sites as a result of the need to characterise sediment prior to disposal (see Paragraphs 3.5.2.7 - 3.5.2.8 - Solid Waste for further information on dredged material), these data do not allow an assessment of ambient environmental levels as dredging sites tend to be in industrialised areas and tend to be more heavily polluted than open seabed areas. In order to address this data gap, a baseline survey of Total DDT and TBT in marine sediment was conducted under this Study (ERM 2000c).