engleski

Water quality of mining impacted rivers in the north-eastern Macedonia: I. Physico-chemical parameters and concentrations of dissolved metals/metalloids

The mine waste was recognized as one of the most serious threats for freshwater ecosystems, and it still represents one of the biggest environmental concerns in Macedonia. Some of the reasons for its toxicity are the acidity and high content of trace metals, which could lead to significant loss of biodiversity. Macedonian most significant mineral deposits are Pb and Zn ores, the exploitation of which is carried out in active mines in the north-eastern part of the country, such as Zletovo in Probishtip and Toranica in Kriva Palanka. Two rivers were chosen for this study, the Zletovska River, which receives the waste from the mine Zletovo, and the Kriva River, which receives the waste from the mine Toranica, whereas a location at the Bregalnica River was chosen as non-impacted sampling site. The impact of mining on the surface water quality was studied by measuring physico-chemical parameters, nutrient concentrations, and the concentrations of dissolved macro and trace elements. The sampling was performed in spring (May/June) and autumn (October) of 2012. A number of physico-chemical parameters (temperature, pH, redox potential, conductivity, and dissolved oxygen) were measured on site with a portable multiparameter instrument, whereas the other parameters (alkalinity, turbidity, total dissolved solids, chemical oxygen demand, total hardness, and concentration of nutrients and other anions) were measured in the river water samples in the laboratory by standardized ISO, APHA and EPA methods. The measurements of both trace and macro elements were performed on high resolution inductively coupled plasma mass spectrometer. The Bregalnica River was characterized mainly by slightly alkaline pH and weak contamination with As, Ba, Fe, Mo, Ti, U, V, nitrates and phosphates, which could be connected to agricultural activities, whereas the impact of the mines was not observed. Interesting finding for the Bregalnica River was several degrees higher water temperature compared to the other two rivers, in both sampling periods. The cause of that increase was possibly the mixing of the river water with the hot water from the reservoirs of the nearby situated geothermal system Kezhovica-Ldzhi. Contrary, both Zletovska and Kriva rivers revealed a clear impact of Pb/Zn mines on water quality. The sampling location at the Zletovska River had slightly acidic water, the highest conductivity, total dissolved solids, total hardness, the concentration of CaCO3, the concentrations of macro elements (Na, K, Ca, Mg), as well as sulphates and chlorides. Both sulphates and conductivity are useful indicators of acid mine drainage contamination, because they remain increased even when pH approaches neutral values due to large dilutions. In the Zletovska River increased concentrations of Cd, Co, Cs, Cu, Li, Mn, Ni, Rb, Sn, Sr, Tl, and Zn were also found, among which Cd and Ni belong to priority toxic substances, and Cd even exceeded the environmental quality standards set by the European Water Framework Directive for inland surface waters. Due to low water level, especially high concentrations of several elements were measured in autumn (e.g. Cd: 2.0 μg L-1 ; Mn: 2.5 mg L-1 ; Zn: 1.5 mg L-1). The Kriva River water had slightly alkaline pH and continuous slight increase of several trace elements characteristic for agricultural activities (Ba, Fe, Mo and V). In the Kriva River increased concentrations of metals which could be associated with the impact of the nearby mine, such as Cd (0.270 μg L-1) and Pb (1.85 μg L-1), were found only in spring, possibly due to sediment resuspension during higher water discharge, indicating probable sediment contamination by mining waste. The results obtained in this study revealed severe impact which the active mines Zletovo and Toranica have on the water quality of the rivers receiving their waste (Ramani et al., 2014). The need for the continuous monitoring of those rivers should be emphasized, as well as the necessity to investigate possible detrimental effects of mining waste on the aquatic organisms.

metals; rivers; water quality

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