Metals in Aquatic Ecosystems: Mechanisms of Uptake, Accumulation

Metals are essential cofactors for bio-chemical processes, including oxidative phosphorylation, gene regulation and free-radical homeostasis. Abnormalities in metal ions concentration in organisms, lead towards the eco-physiological hazards in the aquatics. In aquatic organisms, metal absorption involves transfer of metals to the circulatory system following: uptake by the apical membrane; movement through the cell as well as interaction with intracellular ligands and efflux across the basolateral membrane. Sequestration of metals in an immobilized form occurs throughout the various tissues and organs involved in pathways for metal uptake, transport, utilization and release. Metallothioneins, metal binding proteins, regulate the essential metals (Cu, Zn), detoxify the toxic metals (Cd, Hg) and play key role to the sequestering metals. Plasma proteins play the central role in metal transport in the vertebrates. Besides, blood cells in aquatic invertebrates, hemocytes in mollusks concentrate a variety of metals. Aquatic organisms utilize renal, digestive pathways and diapedesis for the excretion of a variety of metals.