Trace Elements in Sediments of Rivers Affected by Brown Coal Mining: A Potential Environmental Hazard

Brown coal remains an important energy source in Europe, including countries such as Germany, Poland, the Czech Republic, and Greece. Open-pit mines disturb the environment in terms of air quality, hydrology, and chemical and biological transformations in rivers receiving mine waters. In the present study, we assessed the impact of mine waters from four brown coal open-pit mines on the contamination of river sediments. Chemical analysis included the quantification of 62 elements, including heavy metals (HMs) and rare earth elements (REEs). The contamination of sediments by HMs was evaluated using the contamination factor (CF), the pollution load index (PLI), and the Nemerow multi-factor index (PI). The potential toxic effects of HMs on aquatic organisms were assessed using the potential ecological risk index (PERI). Detailed analysis of chondrite-standardized concentrations of REEs was performed to describe the effects of mine water on their pattern in sediments. Cluster analysis (CA) and principal component analysis (PCA) were employed to divide study sites into groups and to evaluate the combined effect of sediment texture and site location on HMs and REEs in sediments. The study showed that after mine water discharge, there is a decrease in HM and REE concentrations in sediments. The decrease in each element’s concentration in sites located 100 m downstream of the discharge was caused by washing out of the finest fractions of sediments by mine waters.