An assessment method for heavy metal cumulative risk on farmland soil in the mining area: A case study of the Xiaoqinling gold mining area

The accumulation of heavy metals in soil is generally sourced from metal mineral exploitation activities in the mining area, and hence the key to assessing the cumulative effect and risk of heavy metal accumulation in soil is to choose scientific evaluation standards and methods. In this paper, the background of heavy metals and the meaning of the soil environmental quality standards were briefly explained, and the average heavy metal concentrations in adjacent areas with the same or similar conditions were taken as the background of heavy metal accumulation. In 2011, case study was performed in the Xiaoqinling gold mining area. 80 groups of heavy metal samples were collected in the agricultural soil. The experimental results showed that the proportion of lower risk samples of heavy metals to total samples was in order of Hg>Cd>Pb>Cu, whereas the contribution rate of mining activities on the soil heavy metal accumulation was in order of Hg>Cu>Pb>Cd>Zn. There existed no risk of Cr, As and Zn in soil in spite of slight accumulation of these elements. The risk area of Hg reached 187.77km2, accounting for 47.08% of the total survey area. And the area of middle and high risk possessed 99.55km2, suggesting an extremely serious situation. The research results provide the scientific evaluation of the cumulative effects and contribution of mining activities on the heavy metal accumulation in soil and point out the way forward in the aspect of the soil pollution prevention.