FATE AND EFFECTS OF SOLUBLE OR SEDIMENT-BOUND ARSENIC IN OYSTERS (CRASSOSTREA-GIGAS THUN)

Contaminated sediments are a possible source of stress to the benthic biota. In order to examine this way of transfer concurrently with dire ct exposure, oysters were exposed to As dissolved in natural seawater or loaded to particles. The sediment used as a vector of transfer was a mud from a coastal area devoted to oyster culture, the finest partic les of which have been selected. It was submitted to experimental cont amination then to in vitro desorption tests, in which enzymes and pH c hanges were used to mimic the digestive processes in Molluscs. Althoug h different enzymes or pH induced the desorption of 3 to 24% of sedime nt-bound arsenic, the accumulation of this element in the soft tissues of oysters remained low after exposure to contaminated particles. The uptake of soluble arsenic was also limited although checking the leve l of arsenic in seawater every day revealed no significant decrease of the contaminant in the experimental medium. However, cytological effe cts were noted in oysters exposed to sediment-bound arsenic and moreov er to soluble arsenic. They consisted of structural alterations of mit ochondria and nuclei, suggesting a disturbance of both the cellular re spiratory metabolism and nucleotid incorporation.