Distribution characteristics and source identification of heavy metals and safe utilization in surface soils from high-selenium regions in China

The research of heavy metals in high-selenium soil is critical for the land utilization. Langao County in Southern Shaanxi, a typical high-selenium area in China, was studied to examine the distribution, source identification, safely utilization of heavy metals in surface soils. Content of heavy metals (As, Cr, Cu, Ni, Pb, Zn, Cd and Hg) were measured in 360 surface soil samples, 12 layered soil samples from Langao County, and 8 surface soil samples from different geological units in other regions. The results show: (1) Except for Hg, the mean concentrations of As, Cr, Cu, Ni, Pb, Zn and Cd were greater than Chinese and Shaanxi province background values. (2) The spatial distribution of heavy metal concentration in surface soil is greater in the northern region and lower in the southern region, which is compatible with the stratigraphic trend (northwest-southeast trend). Langao County has three possible heavy metal sources: (1) Weathering and leaching of rocks or parent materials (As, Cu, Zn, Cd and Hg); (2) Agricultural activities (Cr and Ni). (3) Transportation (Pb). (3) As, Cr, Ni and Cd in surface soils have potential carcinogenic risks. (4) For safe utilization of land, 5.68% of the land area should be strictly protected, 75.90% of the land area should be applied with substitute planting, 18.42% of the land area should be strictly prohibited from planting agricultural products. This research might provide a theoretical foundation for scientific land management in high-selenium area.