Geochemical assessment of potentially toxic elements in river sediments from a highly contaminated mining area - Cavnic, Romania

This study examines levels of contamination and ecological risks associated with potentially toxic elements in alluvial sediments of the Cavnic River Catchment (CRC) in northwestern Romania, a region with a history of intensive polymetallic mining. The accidental discharge of mine water from the Ferdinand gallery (Bolduţ mine) in 2020 contributed to the presence of metal(loid)-rich sediments in the Cavnic River. In the Cavnic mining district, historical underground workings, waste rock dumps, and tailings ponds are potential sources of acid mine drainage. A total of 33 sediment samples were collected from the main river and its tributaries to analyse the concentrations of ten heavy metals and metalloids (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Zn). The analysis was performed using ICP-MS, and the results were interpreted through descriptive statistics, spatial distribution mapping, correlation analysis, hierarchical cluster analysis (HCA), and six pollution indices: geo-accumulation index (Igeo), enrichment factor (FE), contamination degree (CD), pollution load index (PLI), potential ecological risk index (RI), and environmental toxicity quotient (ETQ). Findings reveal significant spatial variability and high levels of Hg, Pb, Zn, and Cu, especially in areas near former mining sites such as waste rock dumps, tailings ponds, and ore processing facilities. The risk assessment indicates that sediments contaminated in the CRC could pose health risks, especially where Hg, Pb, and As concentrations are high. Several sampling points exceeded geochemical thresholds, with some locations showing very high contamination (CD > 24) and extreme toxicity (ETQ > 300). The combined use of geostatistical methods and pollution indices highlights the ongoing environmental impact of abandoned mining operations in the CRC. The Cavnic River Catchment is located in a region of high ecological and cultural importance included in the proposed Gutâi-Maramureş UNESCO Global Geopark. These results emphasise the importance of ongoing environmental monitoring and the need to implement effective clean-up strategies to reduce ecological and human health risks.