Vertical Distribution and Persistence of Heavy Metals in Soils from Inactive Mining Dumps in the Jiu Valley, Romania

Mining waste dumps represent important long-term sources of environmental contamination in former coal mining regions. The Jiu Valley, one of Romania’s most important historical coal mining areas, contains numerous inactive mining dumps that continue to influence soil quality after mine closure. The present study evaluates the vertical distribution and persistence of heavy metals in soils collected from fourteen inactive mining dumps located within the former mining perimeters of Uricani, Lupeni, Vulcan, Livezeni and Petrila. Concentrations of chromium (Cr), copper (Cu) and nickel (Ni) were compared for all investigated dumps, while zinc (Zn), cobalt (Co) and lead (Pb) were included where available in the dataset. The results showed that Cr concentrations ranged between 33.48 and 38.43 mg/kg in the surface layer and between 31.47 and 36.12 mg/kg in the deeper layer. Copper concentrations varied between 54.19–58.92 mg/kg and 47.42–51.55 mg/kg, respectively, while Ni reached maximum values of 87.44 mg/kg in the 0–20 cm layer and 83.07 mg/kg in the 20–40 cm layer. A general decrease in concentration with depth was observed, but the reduction was relatively moderate. The calculated decreases ranged between 3.2–8.7% for Cr, 8.6–17.1% for Cu, 2.9–7.9% for Ni, 15.5–20.6% for Zn, 8.2–12.4% for Co and 19.4–25.3% for Pb. The limited decrease between the two investigated layers indicates that contamination is not restricted to the surface horizon but persists within the waste material. The results support long-term environmental monitoring and rehabilitation strategies for inactive mining dumps in the Jiu Valley.