engleski

Evaluation of dietary metal exposure of Squalius vardarensis dwelling in mining impacted rivers in the north-eastern Macedonia

Fish are frequently selected as the organisms of choice in aquatic biomonitoring due to their top position in the biotic communities and their sensitivity to low concentrations of environmental pollutants. Among other pollutants, metals represent a serious threat to the aquatic environment, since they are not biodegradable and can accumulate in the sediments and biota, including fish. For normal cellular metabolism, fish require essential metals which may be taken up from water, food and/or sediments in varying degrees. Metals are taken up to fish through skin, gills and gastrointestinal tract. In the last decade there is a growing concern that dietborne metal uptake may be of equal or greater importance than the waterborne for native fish. Accordingly, in the present field study gastrointestinal tissue was selected as an indicator organ for evaluating dietary metal exposure of freshwater fish Vardar chub (Squalius vardarensis) in two mining impacted rivers (Zletovska and Kriva) and in less contaminated river (Bregalnica). High contamination of the aquatic systems by the waste from active mines can seriously affect the quality of surface water, with the regard to metal/metalloid levels, and consequently influence the aquatic life. The exposure of Vardar chub to dietborne metal levels in three differently impacted rivers by Pb/Zn active mines Toranica and Zletovo, situated in the north-eastern Macedonia, was assessed by measuring 22 trace and 4 macroelements in sub-cellular gastrointestinal tissue fraction, cytosol, in order to determine the levels of bioavailable metal form. Cell cytosol was isolated from posterior part of gastrointestinal tissue by homogenisation at 4°C in 5 volumes of homogenising buffer (100 mM Tris/Base, pH=8.1) containing 1 mM DTT as a reducing agent and 0.5 mM PMSF and 0.006 mM leupeptin as inhibitors of proteolitic activity. The homogenates were centrifuged at 50000xg for 2 hours (4°C), resulting in water soluble cytosolic fraction (S50), which was 10 times diluted for determination of trace and 100 times for determination of macroelements. Metal measurements were carried out by high resolution inductively coupled plasma-mass spectrometer (HR ICP-MS). The sampling campaigns were performed in spring (May/June) and in autumn season (October), which coincided with chub spawning and post-spawning period. Significantly higher gastrointestinal metal concentrations in the mining impacted Kriva River compared to the Bregalnica River in both seasons were found for Se, in the mining impacted Zletovska River for Li, Rb, Mo, Cs, Tl, U, Co, Ni, Cu, Sr, As, Ca, while the highest V, Mn, Zn and Ba concentrations were found in the agriculturally contaminated Bregalnica River. Although dietborne metal levels usually do not directly reflect total dissolved metal concentrations in water, spatial variability of gastrointestinal cytosolic metal levels were in accordance with higher Ba and V total dissolved concentrations in the Bregalnica water and Co, Cs, Cu, Li, Ni, Rb, Sr, Tl and Ca in the Zletovska water. Moreover, seasonal differences of metal concentrations in water were followed by gastrointestinal metal variability, which was evident as higher Pb levels in Bregalnica in spring, higher Tl and Sr in Zletovska in autumn, and higher Cd and Pb levels in the Kriva River in spring. In addition, significant correlation of cytosolic Pb and chub total length and body mass (r=0.5, p<0.01) from the Kriva River in spring indicated size dependence of Pb accumulation in chub. Cytosolic gastrointestinal metal levels of Vardar chub evidently reflected metal concentrations in the river water and, therefore, reflected significant impact of the nearby mine on the Zletovska River and occasional contaminations of the Kriva River.

chub ; mining ; intestine ; metals

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