Cadmium, Biomarker, Pollution, mRNA, Mytilus edulis, Metallothionein, Metallothionein - metabolism, Zinc - metabolism, RNA, Messenger - genetics, Transcriptional Activation, Gene Expression Regulation, Cadmium - metabolism, Blotting, Northern, Animals, Metallothionein - genetics, Protein Isoforms - metabolism, Copper - metabolism, Bivalvia - genetics, Protei...