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Characterisation of bio-indicator species

MEL's Radioecology Laboratory has been studying metal contamination in temperate and tropical environments to characterize and validate the bioindicative value of several local marine species to be used in coastal monitoring programmes. Presently, a particular effort is focussed on tropical regions where urbanization and industrialization are constantly growing whereas there is little information available about possible associated impacts in the coastal environment.

The lagoon of New Caledonia is an excellent model for studying metal pollution in tropical coastal marine ecosystems because it is subjected to the input of large amounts of contaminants from land-based mining activities (mainly Ni). Four species commonly found in the lagoon are currently being investigated to assess their usefulness as bioindicators: an edible clam, a brown alga and two oysters. Metal accumulation and retention were determined for seawater, sediment and food exposure pathways. Seven metals that are directly or indirectly discharged by mining industries were particularly studied using the following radiotracers: Ni-63, Co-57, Cr-51, Mn-54, Cd-109, Zn-65, Ag-110m. So far, results indicate that all investigated metals are readily incorporated and strongly retained in the tissues when organisms are exposed via seawater or food. They also indicate a very low bioavailability of sediment-bound metals (3 to 5 orders of magnitude less bioavailable than from seawater). Mathematical modelling indicates that food represents the main source of intake (> 80%) for most metals in the bivalves. The alga and the two oyster species appear to be excellent bioindicators showing a rapid response time in metal uptake with a suitable potential to furnish necessary information on ambient contamination levels. Presently, work is being conducted to validate these findings, both experimentally at MEL and under existing environmental conditions in the lagoon of New Caledonia.