Seasonal Variation in Elements in River Water and Reassessment of Environmental Impact in the Bor Mining Area, Eastern Serbia

This study evaluates the impact of long-term mining activities on stream surface waters in the Danube Basin in eastern Serbia. Seasonal variations in water chemistry were investigated during three hydrological periods to assess current contamination levels and temporal changes following recent environmental protection measures. The highest element concentrations were recorded during the autumn low-flow period. In contrast, the lowest concentrations occurred during the snowmelt season, indicating a strong influence of seasonal hydrological conditions on contaminant distribution. In streams located downstream of mining facilities, element concentrations were additionally controlled by anthropogenic inputs associated with mining activities. Elevated concentrations of SO42− (1054 mg/L), Cu (393 µg/L), and Mn (2064 µg/L) were detected compared with background values characteristic of non-contaminated streams (e.g., SO42−~100 mg/L, Cu~20 µg/L, and Mn~20 µg/L). Recent environmental protection measures, including the neutralization of mining wastewater before discharge into rivers, have substantially reduced contamination levels. Compared with historical periods when untreated wastewater was directly discharged into river systems, concentrations of Fe, As, Cu, and Mn decreased by approximately 2650-, 900-, 740-, and 6-fold, respectively. In contrast, sulfate concentrations remained relatively unchanged, indicating persistent mining-related pollution and suggesting sulfate as a reliable indicator of contamination in similar mining environments. Overall, the results demonstrate partial recovery of the aquatic system and improved water quality over time; however, elevated concentrations of SO42−, Mn, and Cu indicate ongoing environmental impacts of mining activities and highlight the need for long-term environmental monitoring and management.