FLUCTUATIONS OF CADMIUM, COPPER, LEAD AND ZINC CONCENTRATIONS IN-FIELD POPULATIONS OF THE PACIFIC OYSTER CRASSOSTREA-GIGAS IN THE BAY OF BOURGNEUF (ATLANTIC COAST, FRANCE)

Three groups of oysters Crassostrea gigas were selected according to t heir age and/or size. They were cultivated from March 1982 to May 1984 in a coastal area (Bay of Bougneuf, France), devoted to oyster cultur e. Monthly sampling was carried out from each group of animals, allowi ng the determination of the dry weight and metal concentrations (Cd, C u, Pb, Zn) in three groups of tissues: gills and labial palps, viscera l mass and ''remainder''. Concentrations of Cd, Cu, and Zn decreased i n late spring and early summer concomitantly with increasing weight of soft tissues (due to sexual maturity). The concentration of Pb fluctu ated more widely. Nevertheless, by using temporal series analysis, sim ilar trends were observed for Pb as for other metals concerning both s easonal changes and relation to weight. The highest concentrations of Cd and Pb were observed in visceral mass; whereas, gills and palps exh ibited the highest concentrations of Cu and Zn. Interannual variations of Cd, Cu, Pb and Zn concentrations due to weight changes were observ ed. No significant correlations were noted between Cd and Cu concentra tions in oysters and their environmental sources (seawater and seston) . If data corresponding to an episodic Pb contamination observed in Au gust 1982 were excluded, a significant positive correlation was observ ed between Pb concentration in organisms and filtered water. A signifi cant negative correlation between Zn concentrations in seston and oyst ers was noted. Metal concentrations in faeces did not show a seasonal tendency, and they were not correlated with metal concentrations in se ston. Only Cu concentrations were higher in the faeces than in the ses ton. Cu concentrations in oysters increased with increasing age and we ight. Cd and Pb concentrations were not correlated with either age or weight. Zn concentrations in oysters increased with age, except in you ng oysters where an initial decrease was observed.