Heavy metals pollution and the identification of their sources in soil over Xiaoqinling gold-mining region, Shaanxi, China

Abstract

In order to determine the characteristics of heavy metals’ pollution and identify their sources in the soil over the Xiaoqinling gold-mining region, Shaanxi, China, 133 soil samples were collected over the region, one sample was from a close point as background, and concentrations of Hg, Pb, Cu, and As in all samples were analyzed. Results indicated that the soil was polluted by these heavy metals, as their concentrations in the soil over the studied region were higher than that in the background zone. In addition, the result indicated that these metals had their specific spatial characteristics. Among the samples, those with higher concentrations of Hg, Pb, and Cu were mainly collected from the Shuangqiao river alluvial terrace area, the loess ravine tableland, and the piedmont alluvial–pluvial inclined tableland, which are the areas of gold-mining activities. Meanwhile, the samples with higher concentrations of As were distributed over the loess ravine tableland around Tongguan County, where agricultural activities were conducted intensively. Furthermore, the sources for all the heavy metals Hg, Pb, Cu, and As in the soil over each landscape were determined through analyzing the concentration correlation of these metals and comparing the maps of metal concentration distribution and land-use types. In Yellow river–Weihe river alluvial plain area, these heavy metals were mainly from agricultural activities. In the other landscapes, As was also mainly from agricultural activities; the other metals were contrarily from the gold-related activities. Interestingly, the correlation coefficients of As concentrations with Hg, Pb or Cu concentrations were positive in the samples from Yellow river–Weihe river alluvial plain area, and on the contrary, they were negative in the samples from the other landscapes. This result showed that the correlation can be used as an index to indicate properly the effect of the gold-related or agricultural activities on the heavy metals in the soil and identify their main sources over each landscape. As human activities resulted in the site-specific characteristics in the concentrations and sources of the heavy metals in each landscape, site-specific control strategies should be selected intensively to remedy landscape soil pollution. In Yellow river–Weihe river plain area, effective control strategies should be aimed at remedying As pollution caused by agricultural activities; in the other landscapes, Hg, Pb and Cu pollution caused by gold-mining activities should be considered.