engleski

Ecotoxicological evaluation of metallothionein level in selected tissues of estuarine invertebrates

Organisms living in the estuarine habitats, near to urban and industrial areas are often subjected to interactions of varying natural stressors and diverse anthropogenic impacts, possibly modulating environmental trace metals bioavailability. Biomarker metallothionein (MT) belonging to the class of cytoplasmic stress-defense proteins, is particulary responsive to environmental trace metal exposure. Evidently, several abiotic and physiological variables may induce MT concentration in aquatic invertebrate tissues. The present study objective is to evaluate the contribution of natural stressors, salinity and temperature, on tissue-specific MT induction in two common estuarine invertebrates Mytilus galloprovincialis and Carcinus aestuarii under constant and fluctuating laboratory conditions. Spectrophotometric MT and cytosolic metal determinations (Cd, Zn, Cu)provided by AAS were expressed on wet tissue basis (µ gg-1). The results indicate that under short-term, 8-12 days of acclimation to diluted sea water (DSW ; 15‰ 10-12oC) crabs and mussels display distinct, tissue-specific responses. The most pronounced effect of hypoosmotic stress was time-dependent elevation of branchial MT in the anterior (23.0 µ gg-1 ) and posterior gills (26.4 µ gg-1 ) of C. aestuarii exceeding by 2.4- and 2.9- fold level in control crabs (SW 38‰ ) showing high positive correlation with cytosolic zinc ; (r) 0.71 and 0.99 respectivelly. The hepatopancreas control MT level (278 µ gg-1) was slightly reduced in crabs exposed to DSW. Under the same laboratory conditions alteration of mussel MT in both, digestive gland (154 µ gg-1) and gills (50 µ gg-1) varyed within 30% of corresponding SW controls. Digestive gland hyposaline-induced MT displays decreasing temporal trend in comparison to varying MT level in gills, markedly affected by temperature. The most pronounced MT increase was found in gills of mussels exposed to combined environmental variables, further of optimum ranges (DSW 11‰ 27oC). Additional supportive evidences for tissue-specific, time-dependent responses were obtained in mussels subjected within 15 days to low ambiental cadmium (5µ gCdl-1) under the fluctuating salinity-temperature conditions provided by laboratory running estuarine water supply system. Digestive gland, Cd-induced MT was significantly elevated several days prior to level in gills, surrpassing confidence interval attributed to natural stressors. Considering Cd-mediated signal to noise ratio, related to natural stressors, branchial tissue appears to be less appropriate for biomonitoring purpose than digestive gland/hepatopancreas. Assuming complexity of estuarine situation, for conclusive evaluation on preferential tissue usage, the interactive effects of other environmental variables on tissue specific MT modulation should be examined.

metallothionein; biomarker; hypoosmotic stress; cadmium exposure; Mytilus galloprovincialis; Carcinus aestuarii

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