Field and Experimental Study of the Bioaccumulation of Some Trace Metals in a Coastal Food Chain: Seston, Oyster (Crassostrea Gigas), Drill (Ocenebra Erinacea)

Abstract

From March 1982 to May 1984, monthly sampling has been carried out in a comparatively un-polluted coastal area (bay of Bourgneuf, France), allowing the determination of Cd, Cu, Pb and Zn concentrations in water and in the different links of the studied food chain. Except for Pb, the higher the metal level, the higher the trophic level. In order to determine if this situation results from a real biomagnification in the food chain or from specific abilities to concentrate trace metals, oysters and drills were exposed to metals frcm different sources. Young oysters were exposed for 4 weeks, simultaneously to Cu and Pb, through seawater and/or food. The metals were analyzed in phytoplankton in order to evaluate the daily food supply of metals to oysters. The body burden of Cu and Pb in oysters and their concentrations were evaluated after 12, 20 and 28 days of exposure. In controls and oysters contaminated via food the body burden of Pb decreased during the experiment. This indicates that the quantity of Pb eliminated was higher than the input of this metal. Moreover, the direct uptake from water led to body burdens approximately 100 times higher than those reached after contaminated food ingestion. Contaminated seawater + food did not induce any significant additional increase. For Cu, the body burden increased during the experiment in controls as well as in oysters fed with contaminated phytoplankton. This means that the quantity of Cu eliminated is lower than the input of this metal. However, the body burdens induced by exposure to contaminated seawater or seawater + food are at least ten times higher than those registered in oysters exposed via phytoplanktonic food. This result, as well as the high concentration factor of Cu in C.gigas (approximately ten times higher than in phytoplankton) emphasize the ability of oysters to concentrate Cu. This could explain the increase of Cu concentration in increasing trophic levels observed in the field study but the accumulation of Cu from food is significant and could play a role in chronic exposures. Drills were placed for 6 weeks in plastic net bags containing no food or food with different levels of metals. No significant differences were observed between the levels of Cd, Cu and Zn in controls and in drills of the three groups, indicating that these levels do not depend on the food.