In situ potential use of metallothionein as a biomarker of cadmium contamination in Ruditapes decussatus.

Cadmium (Cd) and metallothionein (MT) concentrations were analysed in the gills and digestive gland of clams Ruditapes decussatus collected from two sites of the Gulf of Gabès (Tunisia) which differ by their degree of pollution. The effect of biotic (maturity stages, protein, sex and body mass) and abiotic factors (temperature, salinity, site and season) on Cd and MT concentrations showed that in the reference site "Bordj d'Ungha" physiological changes caused by gamete development and maturity contributed more to changes in MT concentrations than the bioavailable Cd concentrations; whereas, in the contaminated site "El Hofra", MT induction responded to raised Cd bioavailabilities rather than to physiological changes. With a view to using MTs as metal exposure biomarker in monitoring program, our results show that the analysis in the digestive gland seem to be more relevant than in gills, and that males appear as the most promising candidates compared to females in the determination of this biomarker.