Ecological Risk Assessment Based on Total Amount and Chemical Species of 5 Heavy Metal Elements in Soil Around Mining Area in Southern Shaanxi

In order to investigate chemical species and ecological risk of the 5 heavy metal elements (Cu, Pb, Zn, Cd and As) in the soil around mining area in southern Shaanxi, 529 samples were collected by grid sampling method, in which, chemical species of the 5 heavy metal elements in 30 samples were extracted by improved BCR extraction method. Total amount and each chemical specie amount were analyzed by inductively coupled plasma atomic emission spectrometry. Analysis of enrichment degree and homology of target elements was carried out on detection data by descriptive statistics, normal distribution test. Pearson correlation test and pricipal component analysis. Ecological risk was evaluated by potential ecological hazard index method. Activity and source of target elements were analyzed by RAC and RSP methods, respectively. It was shown that the maximum determination values of the 5 target elements were 3.88-30.53 times than background values (survey data in 2006) of Shaanxi province, and the proportion of samples with determination values of the other 4 target elements exceeded screening values of GB 15618-2018 were 8.0%-27.0% except for Cu. The variation coefficients of determination values of the 5 target elements ranged from 42.5% to 228.6%, indicating that the 5 target elements were accumulated to varying degrees in the soil around the mining area and the distribution was uneven. Cu, Pb and Zn might come from the same sources, and Cd and As might come from the independent source. The average and maximum values of total potential ecological hazard index were 29.42, 406.22, which revealed that the ecological risk of soil was in safe degree, whereas the soils were polluted seriously by Cd, As in some areas. The residual specie proportion of the 5 target elements ranged from 47.3% to 70.7%, and the sum proportion of water-soluble and weak acid-soluble species ranged from 12.5% to 34.8%, indicating that the main chemical specie of these 5 target elements was the stable residual specie, but there existed the risk that elements in the 2 chemical species might migrate and convert into soils. As found by RAC evaluation indexes, the 5 target elements reached moderate ecological risk level based on average values. Among which, Zn and Cd were belonged to severe ecological risk level based on maximum values, and Cu was belonged to extremely severe level based on maximum values. As found by RSP evaluation indexes, Pb was belonged to non-pollution level based on maximum values, As, Zn and Cd were belonged to moderate pollution level based on maximum values, and Cu was belonged to severe pollution level based on maximum values, indicating that human activity was the main factor that affected Cu and the other 4 target elements pollution might come from nature formation.