Monitoring coastal contamination by trace metals pollution using mollusks bivalves as quantitative bioindicators is widely performed in many international biomonitoring programs. For this purpose, studying mercury dynamic in marine mussels is a reliable tool. In situ experiments on uptake and elimination kinetics were conducted in three Mediterranean sites, chosen on the basis of their contamination levels. Mussels were transplanted from a clean area to a highly contaminated one and then transferred back to a clean site. This approach makes it possible to define bioaccumulation factors and uptake and elimination rates consistently with the real environmental conditions.