This paper is the result of environment geological survey engineering.
Objective Luanchuan County is a typical molybdenum mining area in China. It is of great significance to figure out the pollution status of heavy metals in the agricultural soil around the molybdenum mining area for regional environmental prevention, mine ecological restoration and sustainable development of mining industry.
Methods This study collected 54 topsoil samples from the agricultural land in Chitudian Town around the typical molybdenum mining area. The concentrations of Cd, Cu, Zn, Pb, Hg, As, Cr and Ni were analyzed for obtaining the spatial distribution characteristics of these heavy metals, and the heavy metal pollution, ecological risk and human health risk was evaluated by the geo-accumulation index method, potential ecological risk index method and health risk index method, respectively.
Results Compared with the risk screening values for soil contamination of agricultural land, Cd, Cu, Zn and Pb are the main elements exceed the standard values, As concentrations in a few samples exceeds the standard values, and the concentrations of Hg, Cr, Ni in all the samples did not exceed the standard values. The spatial distribution characteristics showed that area A (around the molybdenum mining area) is the main distribution area with high concentrations of Cd, Cu, Zn and Pb, which decreased gradually with the increase of distance. The order of percentages of sample sites with heavy metal concentrations exceeding the risk screening values is area A> area B> area C. According to the values of geo-accumulation indices based on background values for heavy metals in topsoil of Henan Province, the pollution levels for Hg, As, Cr and Ni in the soils were between unpolluted to moderately polluted, and the pollution level of Cd was moderate to heavy polluted, while the pollution levels of Cu, Zn and pollution level of Pb is between moderately polluted to strongly polluted. Light to heavy degree, showing the order of pollution degree are Cd > Pb > Zn > Cu and area A> area B>area C; In terms of potential ecological risk, study area shows slight ecological risk, where the risk in area A is higher than that in other areas (B and C), and Cd posed most highest risks. The non-carcinogenic health risk index is less than 1, with the order of Cr > As > Pb > Ni > Cd > Cu > Zn > Hg, and the carcinogenic health risk index is less than 1×10-4, with the order of Ni > Cr > As > Cd, which is an acceptable risk level. The carcinogenic and non-carcinogenic health risk indexes for children are higher than those for adults.
Conclusions The pollution of heavy metals (Cd, Cu, Zn and Pb) in the agricultural soil around the molybdenum mining area was existing, reaching the levels of moderate to strong pollution, but the overall ecological risk is low, and the risks of non-carcinogenic and carcinogenic health were within an acceptable range. Children are more sensitive and vulnerable to heavy metals, so it is necessary to strengthen the protection for the children.
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