Seasonal dependence of cadmium accumulation and Cd-binding proteins in Mytilus galloprovincialis exposed to cadmium

At different periods of the year specimens of Mytilus galloprovincialis wer e exposed to 0.5 mu g Cd/ml seawater for 7 days. Concentrations of trace el ements (Cd, Zn, Cu and Fe) and Cd-binding proteins in gills, viscera, muscl e and mantle were determined after 1 weeks exposure. Cadmium accumulation w as higher in May and June and was tissue dependent; it was highest in the g ills and decreased in the order: gills > viscera > mantle and adductor musc le. Significant seasonal variations of zinc, copper and iron, were also fou nd, in both exposed and control molluscs. The percentage of Cd distribution between cytosol and pellet changed during the year; a clear shift from the particulate fractions to the cytosolic fractions was measured during May a nd June, especially in the gills. Metallothionein (MT) was the main ligand responsible for Cd accumulation, and this protein reached a maximum between May and June. Inclusion of mercaptoethanol during the purification procedu re was found to improve MT isolation by gel chromatography. In the absence of mercaptoethanol, MT showed polymerization patterns which were season dep endent and temperature independent, whereas its concentration was increased in mussels kept at higher temperature. (C) 1999 Elsevier Science Inc. All rights reserved.