Speciation and distribution of mercury in soils around gold mines located upstream of Miyun Reservoir, Beijing, China

Long-term mining and smelting activities have contaminated gold mine soils and sediments close to Miyun Reservoir. Several studies have reported concentrations of mercury (Hg) in the Miyun Reservoir area, but this paper presents the first comprehensive study of the distribution and speciation of Hg in this area. The gold mines upstream of the Miyun Reservoir were selected for study. Our results indicate that the total Hg contents in soils (average of 9.57 mg·kg− 1) were higher in the study area than background values for Beijing surface soils. Samples suggest that Hg distributed as from a point source around the tailings, suggesting that tailings are the major sink for anthropogenic Hg in the study area. Total Hg had a negative correlation with cation exchange capacity, while pH and total organic carbon showed little correlation with total Hg. Hg in soils existed mainly in residual form, with bioavailable Hg accounting for only 0.30% of total Hg. High pH conditions were conductive to the formation of Fe-Mn oxide-bound Hg in mine soils. The Müller geoaccumulation index used to assess pollution indicates that Hg had very serious pollution levels within the study area, requiring urgent management to prevent residual Hg becoming exchangeable through humic acid conversion and entering the watershed.