engleski

Accumulation of metals and metalloids in the liver and gills of Vardar chub (Squalius vardarensis) from three mining impacted rivers in north eastern Macedonia

Mining activity can seriously affect the quality of surface water, especially regarding the levels of trace elements, which present a serious threat to the aquatic organisms because of their toxicity, persistence and bioaccumulation. The aim of this study was to assess bioavailability of metals and metalloids in the river water based on their accumulation in two target organs (liver and gills) of Vardar chub (Squalius vardarensis) from three rivers in north-eastern Macedonia, agriculturally impacted Bregalnica River and two mining impacted rivers, the Zletovska and the Kriva River. For the assessment of metal accumulation, 12-30 chub specimens were caught per site in spring (May/June) and autumn (October) of 2012. Metal/metalloid concentrations were determined by high resolution inductively coupled plasma mass spectrometer in the soluble cytosolic fractions of gills and liver, obtained after tissue homogenization and centrifugation at 50 000xg. Under conditions of low metal exposure, following ranges of metal/metalloid concentrations were measured in the chub liver: <1 μg L-1 for Tl ; 1-10 μg L-1 for As, Cd, Co, Cs, Pb, Sr, and V ; 10-100 μg L-1 for Ba and Mo ; 100-500 μg L-1 for Mn, Rb, and Se ; and >1000 μg L-1 for Cu, Fe, and Zn. In chub gills, concentration ranges slightly varied, as follows: <1 μg L-1 for Cd, Tl, and V ; 1-10 μg L-1 for As, Co, Cs, Mo, and Pb ; 10-100 μg L-1 for Ba, Cu, Mn, and Se ; 100-500 μg L-1 for Rb and Sr ; and >1000 μg L-1 for Fe and Zn. The comparison between two organs indicated higher basal concentrations of several elements in the liver: As, Cu, Mn, Mo, Se, Tl, and V were higher 2, 30-50, 3-7, 8, 2-3.5, 2, and 9 times, respectively, in both seasons, whereas Fe was 9 times higher only in autumn. Higher concentrations in the gills were found for Sr (13 times) in both seasons and for Fe and Zn (2 times) only in one season (in spring and autumn, respectively). As a result of increased exposure to metals in the river water, increased bioaccumulation was observed for several elements in both liver and gills of Vardar chub in both seasons, specifically for V in the Bregalnica River, and for Cs, Rb, Sr, and Tl in the Zletovska River. Increased exposure to Cd was evident in both seasons in the Zletovska River, but only in spring in the Kriva River, and accompanied by adequate increase of cytosolic Cd concentrations in both organs. In the Kriva River, dissolved Cd concentrations decreased in autumn and resulted with decrease of cytosolic Cd concentrations in both organs. Increased exposure to Pb in the river water was observed in the Kriva River in spring and in the Zletovska River in autumn, and followed by increase of cytosolic Pb concentrations in both organs. Decrease of Pb concentrations in the river water resulted with partial decrease of cytosolic Pb concentration in both organs. Among listed elements, more pronounced accumulation of Cd, Rb, Tl and V was observed in the liver, of Pb and Sr in the gills, while accumulation of Cs was comparable in both organs. Contrary to above listed elements, several elements did not exhibit signs of bioaccumulation, even under conditions of extremely high exposure in the river water, indicating existence of regulation mechanisms for those elements in chub organism. For example, despite increased concentrations of dissolved Fe in the Bregalnica River and dissolved Mn and Zn in the Zletovska River in both seasons, as well as dissolved Fe in the Kriva River in autumn, increased cytosolic concentrations of these elements were generally not found in the cytosols of chub liver and gills. Only in the Zletovska River, cytosolic concentrations of Mn in spring and Zn in autumn were found increased in the gills (3 times and 30%, respectively) compared with other two rivers, at exposure level of 350 μg L-1 of dissolved Mn and 1.5 mg L-1 of dissolved Zn. However, at much higher exposure level of dissolved Mn in autumn (2.4 mg L-1), increased bioaccumulation of Mn was not observed. In order to exclude chub physiology as a cause of differences in metal/metalloid concentrations between three rivers, we have analyzed their association with the fish size (mass range: 13.86-307.89 g), sex (43% females, 57% males) and season, using the data obtained at less impacted Bregalnica River. The significant associations with chub mass and sex were determined for several elements, but only for cytosolic Ba concentrations in the liver and for cytosolic Mn concentrations in the gills they were determined in both seasons. Negative correlations with chub mass and higher concentrations in males were obtained for Ba, whereas positive correlations with the chub mass and higher concentrations in females were obtained for Mn. Seasonal differences were also observed, with 2-3 times higher concentrations of Cu and Sr in both organs in spring and Fe and Zn in the gills in spring and autumn, respectively. Elements which have been found to accumulate in chub liver and gills due to increased exposure to metals in water (i.e. Cs, Rb, Tl, Cd, Pb, and V) generally showed no association with the chub size, sex or season. Integrated approach to estimation of metal pollution of river water requires linking of data on concentrations of dissolved metals in water with data on metal accumulation in target organs of indicator organisms. In the cytosol of liver and gills of Vardar chub (Squalius vardarensis), increased concentrations of Cd, Cs, Pb, Rb, Sr, Tl, and V were determined in association with increased concentrations of these elements in the river water, whereas, at the same time, their dependence on fish physiology was not established. This indicates the possibility of applying cytosolic concentrations of these metals in chub liver and gills in investigative monitoring as indicators of increased biological availability of metals in the river water.

chub ; metals ; liver ; gills ; mining

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