BIOAVAILABILITY AND TOXICITY OF SEDIMENT-BOUND LEAD TO A FILTER-FEEDER BIVALVE CRASSOSTREA-GIGAS (THUNBERG)

Two different approaches were used to study the bioavailability of sed iment-bound lead, In vitro techniques simulating the potential metal d esorption under conditions prevailing in the digestive tract were assa yed on a contaminated sediment, An experimental model of a food chain was designed to determine the retention of lead in the soft tissues of oysters according to the environmental source of the metal (water or sediment). Neither enzymatic action nor leaching at low pH (both aspec ts of digestion) induce the release of important lead amounts from par ticles, Therefore, after 3 weeks of exposure, the retention of lead fr om the trophic source is lower (1%) compared with direct contamination (5%), Lysosomes are the major intracellular structures responsible fo r lead storage in the gills, digestive tract and digestive gland, The abundance of lysosomes and their lead amount vary according to the gro ss concentrations in the soft tissues, The cytopathological data are i n agreement with the results about lead accumulation: in oysters expos ed to sediment-bound lead, impairments are not so marked as in individ uals contaminated directly from water but the same organelles are conc erned, Mitochondrial impairments may be related to the effect of lead on cellular respiration processes and changes involving the granular e ndoplasmic reticulum may have an effect on the level of protein synthe sis, Cellular extrusions carrying away numerous lysosomes loaded with lead could account for the balancing of lead incorporation between 2 a nd 3 weeks of exposure.