engleski

Adriatic Coastal Areas: Assessment of metal exposure in mussels Mytilus galloprovincialis by means of a biomarker

Among the various types of biomarkers, applied as diagnostic and prognostic tools for marine pollution monitoring, metallothioneins (MTs) are extensively used. MTs constitute a family of low-molecular mass proteins, reach on cysteine residues that sequester metals, having a role in the cellular regulation of the essential metals Cu and Zn and in the detoxication of these and other, non-essential, metals such as Cd and Hg. The protective function of MTs by means of additional synthesis, was observed during controlled-exposure of aquatic organisms to a variety of metals (Cd, Cu, Zn, Hg, Ag, Co, Ni). Studies on the regulation of MT gene expression provided evidence that MTs induction by metals is a direct response to the increased intracellular metal concentration, which is mediated through the action of metal-binding regulatory factors. The induced synthesis of MTs, established under laboratory controlled-exposure experiments, was clear biological response to metal exposure. Laboratory observations on MTs as a molecular biomarker of metal exposure have to be validated in the field. Before MTs can be used in the field to assess organismal health or fitness, the knowledge concerning their normal physiological function and the factors that control the levels of MTs in selected target tissue is needed. The criteria for the selection of indicator organism were defined by the MED POL Phase III-Programme. In that Programme, biomarkers were proposed as early-warning pollution monitoring tools to signal the onset of harmful effects at the cellular and subcellular levels. The filter-feeding Mytilus galloprovincialis species completely fulfil the criteria as the indicator organism. The capacity of MT induction is the greatest in the tissue that is active in uptake, storage and extrection of metals like the digestive gland of M. galloprovincialis. Biomarker responses are powerful because they integrate a wide array of environmental, toxicological and ecological factors that control and modulate exposure to metals. However, the same factors may also complicate interpretation of the biomarker responses. Therefore, it is of paramount importance to take into account the potential impact of confounding factors, when interpreting biomarker data. Examples of such confounding factors are the organisms, health, condition index, sex, age, nutritional status, metabolic activity, migratory behavior, reproductive and developmental status, population density, as well as the season, ambient temperature, water salinity etc. Validation of a biomarker proceeds combining the MT data with those on: 1.physico-chemical properties of the ambient water ; 2. biometric data (total mass and length of the organism, mass of the target tissue, shell mass), age, condition index and physiological status ; 3. metal concentrations in the cytosolic, MT-containing fractions. Fluctuations of different magnitude are observed for MT concentrations in the target tissues of indigenous M. galloprovincialis. They reflect individual response of the organism to the impact of the confounding factors (e.g. salinity and water temperature, food availability, age, reproductive cycle). During the presentation the following will be discussed: a) MT levels in indigenous mussels along the gradient of Hg pollution (at different distance from the waste water outlet of ex-chlor alkali plant in Kaštela Bay) ; b) The impact of the season and the mussels, reproductive status deployed over 12 months in the Kaštela Bay ; c) MT and cytosolic Cu levels in the indigenous mussels sampled in the shipyard or marina (Trogir area). As the additional information to the participants of the Workshop, enclosed are the Standard Operation Procedures for the: -Preparation of S50-fraction from the mussel tissue ; -Quantification of mussel metallothionein using differential pulse voltammetry (DPV).

indigenous and transplanted mussels; metal and metallothionein analysis in tissue cytosol

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