[Enrichment Characteristics and Risk Assessment of Heavy Metals in Soil-crop System of Cultivated Land Around a...

In order to assess the ecological risk of heavy metals in the soil-crop system of cultivated land around the mining area, samples of cultivated land soil and crops around the mining area were systematically collected, and their heavy metal content and occurrence forms were analyzed and tested. The biological enrichment coefficient (BCF), Nemero composite index (P_N), potential ecological risk index (RI), and risk assessment index (RAC) were used to evaluate the heavy metal enrichment characteristics, pollution degree, and risk in soil and crops of the mining area. The results showed that the average values of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the soil in the study area were higher than the national and Chongqing surface soil background values. The occurrence patterns of heavy metals in the soil showed that Cd had the highest proportion of bioactive components and was the primary polluting element in the region. Compared with the soil pollution risk screening value for agricultural land, the excess rate of soil Cd reached 71.88%. Compared with the limits of national food safety standards, the excess rates of Cd in rice, corn, and sweet potato were 36.67%, 10.53%, and 6.67%, respectively, with Cd showing strong migration and enrichment ability in soil-crop systems. The Nemero index showed that 75% of the soil in the study area was clean, still clean, and lightly polluted, and 14.06% was seriously polluted. The evaluation of RI showed that slight, medium, and strong ecological risks of heavy metals accounted for 40.63%, 34.38%, and 21.88%, respectively, and the RI above the strong level accounted for only 3.13%. The main potential ecological risk element was Cd, followed by Hg. The RAC risk assessment showed that Cd was mainly high risk, As and Pb medium risk accounted for 34.3% and 18.75%, respectively, and other heavy metals mainly showed low or no risk. The RAC risk assessment results were more accurate than those for crops exceeding the standard. Combined with the RAC risk assessment results and crops exceeding the standard, the Cd risk of soil and crops in the study area was the highest, showing high risk. The second was As and Pb, which were low to medium risk. Hg, Cr, Cu, Ni, and Zn were low to no risk.