FATE AND EFFECTS OF MICROPOLLUTANTS IN THE GIRONDE ESTUARY, FRANCE - A MULTIDISCIPLINARY APPROACH

Important Cd contamination has been observed in the Gironde estuary, F rance, but other metallic and organic pollutants are also present. Sin ce sediment is well-known as a major compartment for the storage of nu merous pollutants in aquatic environments, its contribution as a sourc e of pollutants for the biota has been examined according to different methodologies. Geochemical studies have provided estimates of Cd mobi lity particularly with decreasing pHs and increasing salinity, a resul t in agreement with the relative abundance of exchangeable Cd and Cd b ound to carbonates shown by sequential extraction. When in vitro assay s tended to be more realistic with regard to the digestion process in bivalves, Cd extraction at low pH was lowered but was still important compared to Cu or Zn. Moreover, toxicity of Gironde sediments to copep od and sea urchin larval stages (not to oyster larvae) brought indirec t evidence of the bioavailability of sediment-bound pollutants. Except the aromatic compound perylene, bioaccumulation in bivalves concerns mainly metals. In oysters they were found preferentially in the solubl e phase and, in the cytosol, a strong relationship between cadmium and metallothionein-like proteins has been shown, suggesting a detoxicati on process in this species. This hypothesis is in agreement with the f act that neither cytopathological effects in gills and digestive gland s nor marked changes of condition index were observed. On the other ha nd, no changes in MTLP levels in mussels were induced by metal accumul ation in individuals transplanted from a comparatively unpolluted area (Bay of Bourgneuf). The stability of GST activity may be related to a poor accumulation of aromatic compounds. Changes in MDA concentration , AChE and catalase activities are discussed. Mobility, bioavailabilit y of pollutants, significant responses of biomarkers suggest a potenti al environmental hazard. However, since interspecific differences occu r, is the risk at the level of the whole estuarine ecosystem equilibri um or is it limited to a small number of species?.