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 direct 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 particles of which have been selected. It was submitted to experimental contamination then to in vitro desorption tests, in which enzymes and pH changes were used to mimic the digestive processes in Molluscs. Although different enzymes or pH induced the desorption of 3 to 24% of sediment-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 level of arsenic in seawater every day revealed no significant decrease of the contaminant in the experimental medium. However, cytological effects were noted in oysters exposed to sediment-bound arsenic and moreover to soluble arsenic. They consisted of structural alterations of mitochondria and nuclei, suggesting a disturbance of both the cellular respiratory metabolism and nucleotid incorporation.