engleski

Effects of metals on marine and estuarine organisms

Metals occur in marine environment in various concentration ranges (major metals, minor metals, and trace metals), and in a number of physico-chemical forms. According to their role in living organisms metals can be classified as essential and non-essential. Essential metals are necessary for normal development, growth and functioning of all living organisms (eg. Zn is component of many enzymes ; Cu is functional part of respiratory protein haemocyanin). Non-essential metals (Cd, Pb, Hg, Ag) are usually toxic to an organism, as well as essential metals when present internally at concentrations above the limits of cellular regulatory process. Marine and especially estuarine organisms are continuously exposed to variable concentrations of metals in the water column. Metal uptake by the aquatic organisms depends on the specific and various environmental conditions such as water hardness, salinity, temperature, irradiance, pH, and organic matter content, as well as on the species of an organism. High metal uptake occurs particularly along coasts, which is influenced by anthropogenic heavy metal contamination. In this respect, molluscs, crustaceans and other marine invertebrates are known to accumulate high levels of heavy metals in their tissues and yet survive in these polluted environments. Tolerance of these animals depends on the ability to regulate the heavy metal concentration inside the cell and to accumulate excess metal in non-toxic forms. Marine molluscs (especially mussels and oysters) have a large capacity for accumulation of metal such as Cu, Zn and Cd, and have therefore commonly been suggested as biomonitors of metal contamination. Mechanisms of heavy metal cation homeostasis identified in marine invertebrate cells are the following: binding to specific soluble ligands (metallothioneins, MTs), compartmentalization within membrane-limited vesicles (lysosomes), and formation of insoluble precipitates (granules). Particularly interesting are inducible metal-binding proteins metallothioneins (MTs). In biomonitoring programmes increased level of MTs is used as a biomarker of organism exposure to increased level of specific metals (Cd, Cu, Zn). This fact will be illustrated with two sets of field data: - indigenous populations of Mytilus galloprovincialis collected over three years period along the middle part of Eastern Adriatic coast (project Adriatic) - blue mussels (Mytilus edulis) caged in two areas of the North Sea (project Biological Effects of Contaminants in Pelagic Ecosystems, www.niva.no/pelagic/web)

toxic metals; biomarkers; bioindicator organisms

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