This study provides a means of supplementing existing data on marine environmental contamination and can also serve as a baseline for establishing the effects of development and other impacts over time on marine resources. Measurement of tissue contamination levels in marine species provides a clear indication of the quantities of contaminants that are passing from the environment into the food chain. For the purposes of this baseline Study it was considered important that when selecting the target species for the analyses that they have a degree of relevance to human health and, therefore, species from the inshore commercial fishery were analysed(2)). It was initially suggested that a fixed list of target species be established for both the surveys in the wet and dry seasons and for all of the sampling stations. However, given that fisheries resources in Hong Kong are known to vary markedly both over time and between areas, it was decided that the most numerous species in each catch should be analysed. Initially it was also thought that preference should be given to larger individuals for the following reasons:

• larger individuals would have been exposed to contaminants in the marine environment for longer periods of time, and therefore, may potentially contain higher body burdens (this assumes that the organisms have limited ability to remove contaminants from their bodies through excretion);

• larger individuals are more likely to have had more exposure to benthic sediments (contaminant sink) through direct contact as they occur in the lower half of the water column or through consumption of benthic dwelling organisms; and,

• the larger individuals in fish catches are those more likely to be sold for human consumption and are therefore more relevant when discussing issues pertaining to human health.

Marine resources in Hong Kong waters are known to have become depleted over time through overfishing, and in certain areas, such as North Lantau, through the effects of habitat loss, coastal development and pollution(3)). What was once a fishery dominated by large, slow growing and high value fish species is now dominated by small, short-lived, fast growing and low value species.

The nature of the Hong Kong fishery, therefore, poses constraints on surveys of tissue contamination in fish species. It has become difficult to collect sufficient quantities of tissues for laboratory analysis due to the small size of catches and lack of large individuals. The resultant catches tend to be composed of a small number of mainly young (small) individuals of a variety of different species. However, this is not necessarily a disadvantage to the current work, as analyses of smaller organisms may provide the basis for a worst-case contamination scenario of local marine biota because of the reasons outlined below:

• smaller individuals have larger surface area to volume ratios and thus have proportionally higher body burdens than larger individuals;

• enzymes involved in contaminant detoxification are often not fully developed in younger organisms; and,

• there is a contaminant dilution effect in larger individuals.

This baseline Study is structured to focus on various organic contaminants which owing to technical difficulties in their measurement, are not frequently analysed in Hong Kong's monitoring programmes. As described in the methodology (see Sections 2 and 3), analysis of Total Polychlorinated Biphenyls (PCB), Total Polycyclic Aromatic Hydrocarbons (PAH), organochlorine pesticide (Total DDT) and Tributyltin was undertaken for tissues, and analysis of organochlorine pesticides (Total DDT) and Tributyltin measured in sediments.