Assessment of trace metals and arsenic contamination in water and sediments in a former mining area of the river basin after an ecological disaster, Slana River, Slovakia

Abstract

This study assessed the spatial distribution of trace metals and arsenic in the water and sediment of the Slana River (Slovakia) approximately one and a half years after the 2022 release of mine water from the former Nizna Slana siderite mine. Samples were collected in September 2023 at four river sites from Gocovo to Lenartovce (L1-L4) and at five points within 50 m of the mine-water discharge (S0-S4), and the data were evaluated using non-parametric tests, principal component analysis, contamination factors (CF) and the pollution load index (PLI). At the discharge point, the water contained 149 mg/L Fe, 27 mg/L Mn and 0.29 mg/L As; beyond this point, however, most metals in the filtered river water were below the limit of detection, and only sulphur remained clearly elevated downstream (35.7 mg/L at L2 vs. 6.4 mg/L at the reference site). In contrast, the sediment retained the contamination: As reached 7920 mg/kg and Cd 39 mg/kg at the discharge, exceeding the probable effect concentrations of freshwater sediment quality guidelines more than 200-fold and almost eightfold, respectively, and As remained above this level at the first downstream site (47 mg/kg). While As, Hg, Mn and Ni declined rapidly downstream, S and Al accumulated toward the most distant site, so that the PLI remained uniform along the river (1.06-1.16; p = 0.246). Despite the apparent recovery of the water column, the sediments of the Slana River thus remain a persistent reservoir of arsenic and trace metals and a potential source of chronic exposure for biota; repeated sampling across seasons is needed to confirm this pattern.