Lead accumulation and metallothionein induction in different tissues of mussels (M. galloprovincialis) and clams (C. chione) exposed to various Pb concentrations

Abstract

Heavy metal pollution of coastal areas due to anthropogenic activity has become a global problem with serious environmental consequences. Various marine organisms have been employed as bioindicators for pollution, and expanding the scientific arsenal with such organisms is a continuing research objective. In this study, the effects of Pb pollution in seawater on two bivalves of different habitats were investigated. Mytilus galloprovincialis (a nearshore and intertidal rocky substrate inhabitant mussel) and Callista chione, (a sand-buried smooth clam), were exposed to a wide range of Pb concentrations in seawater for 20 days, followed by a 10-day depuration period, in a laboratory experiment. Gills, mantles and the remaining bodies of the two species were separated and the accumulated Pb was determined. The synthesis of Pb-induced proteins (metallothioneins and/or other proteins) was also investigated in the tissues of the two species by Ellman assays, Coomasie-stained and fluorimetric SDS-PAGE experiments. Our results show that both species exhibit a relatively high tolerance to even very high Pb pollution levels and they accumulate considerable amounts of Pb in their tissues. Zinc levels in the examined tissues are affected in most of the tested conditions. The 10 days depuration period of our experiments was not enough for the complete removal of Pb from the organisms. Biochemical analysis showed that low molecular weight, sulfhydryl-containing proteins (metallothioneins), as well as proteins with molecular weight of about 50 kDa are synthesized in a species-dependent and tissue dependent way, due to Pb accumulation.