Temporal variations of metallothionein and metal concentrations in the digestive gland of oysters (Crassostrea gigas) from a clean and a metal-rich site

The concentrations of metallothionein (MT) in bivalves, a potential biomark er of metal pollution, are variable according to specific organs, the highe st concentrations being encountered in the digestive glands of oysters. Thu s, the present study has been focused on this organ with a view to validate the use of MT as a biomarker in the field, the temporal changes of metal a nd metallothionein concentrations have been examined from March to October 1997 in the digestive gland of resident oysters from a clean site (Bay of B ourgneuf, France) and a metal-rich site, the Gironde estuary which has been shown as the most CD-contaminated marine area in France but is also enrich ed with Cu and Zn. Moreover, oysters from the clean site have been transloc ated to the Gironde estuary over the same period. Taking into account all t he samples collected over the 7 months of the study, MT concentrations in t he digestive gland were positively correlated with weight whereas metal lev els were negatively correlated with weight. However, considering monthly sa mples including specimens from both sites (resident or translocated oysters ), a positive correlation was shown between MT and metal concentrations in autumn (September and October) but not in spring ans summer. These findings limit the interest of using the digestive gland of oysters as the preferre d tissue for the determination of MT concentration as a biomarker. The alte rnative use of gills should be considered.