Spatial distribution and ecological risk of mercury in a small-scale gold-mining area of the upper Ramis basin, Peru

Abstract

As both artisanal and small-scale gold mining are significant sources of mercury release in environmentally sensitive Andean headwater systems. This study investigated the spatial distribution and ecological risk of mercury in a high-intensity small-scale gold-mining area in the upper Ramis basin of Peru. The surface water, soil, and vegetation were integrated by means of an analysis. A total of 141 georeferenced samples were collected, including 69 samples from surface water, 47 samples from soil, and 25 samples from vegetation. Total mercury was measured by a DMA-80 direct mercury analyzer. Descriptive statistics, spatial interpolation, heat maps were used to evaluate the dataset, as well as the geoaccumulation index and ecological risk factor, for soil. Mercury appeared to exhibit a good deal of spatial heterogeneity between those three environmental matrices. The surface water concentrations vary from 0.0005 to 0.0942 mg/L and showed a significant hotspot at the final discharge point of the treatment system. The soil contents varied from 0.0046 to 1.3273 mg/kg, with the concentration mainly in ore stockpiling areas, transport corridors and sectors related to camps. Vegetation concentrations were from 0.0051 to 13.8056 mg/kg, which revealed some localized exposure hotspots close to operational infrastructure and vehicle-related areas. Soil risk indices described a limited set of hotspots with high contamination severity and high to very high ecological risk. Finally, the study found that mercury contaminants in this area of study were not diffuse, but were spatially organised according to the operational structure of mining activity. These integrated measures provide a stronger basis for environmental monitoring and territorial prioritization in high-intensity small-scale gold-mining headwater systems