Mercury distribution and fractionation in soils of a historical Cinnabar mining site (SE, Spain): evidence of contamination hotspots and environmental stability
摘要
This study evaluated Hg contamination and geochemical fractionation in soils from a historical cinnabar mining site located in south-eastern Spain. Four representative environmental compartments were investigated: a furnace slag heap, the mine interior, the mine exterior and the Tía Anica la Ciega cave. Composite soil samples were obtained from 260 sampling points and analysed for total mercury (THg) using direct mercury analysis (DMA-80). Mercury fractionation was assessed through a sequential extraction procedure, and contamination and ecological risk indices were calculated as preliminary screening tools. THg concentrations showed a marked contrast among environmental compartments. The highest concentrations were recorded in the furnace slag heap and the mine interior (128 and 132 mg kg⁻1, respectively), whereas substantially lower concentrations were found outside the mine (1.356 mg kg⁻1) and in the cave environment (5.028 mg kg⁻1). Mercury fractionation revealed a remarkably consistent distribution pattern across all compartments. The mercury sulfide fraction (HgS) was dominant, accounting for approximately 72–75% of THg, whereas the residual fraction represented 28–30%. Organic mercury and strongly bound species were only present in trace amounts. The results indicate that historical mining and ore-processing activities remain the principal source of Hg contamination within the study area. Although contamination levels are extremely high in the furnace slag heap and mine interior, the predominance of HgS and residual fractions suggests relatively low current mobility under existing environmental conditions. The severe contamination is located in the slag heap and inside the mine. The external areas are within the limits established by the relevant legislation for forest use and do not require an immediate intervention. This spatial pattern constitutes one of the principal findings. Nevertheless, the elevated Hg concentrations identified in mining hotspots highlight the need for continued environmental monitoring and further studies addressing mineralogical characterisation, mercury bioaccessibility and long-term remobilisation processes. This study provides new evidence on mercury distribution and geochemical stability in a poorly documented legacy mining district and contributes to the environmental assessment of abandoned cinnabar mining sites.