关中平原土壤重金属生态风险评价——以杨凌示范区为例

将田间调查与分析相结合，测定了杨凌示范区164个农田土壤样品和88个主要农作物样品中重金属As、Cd、Hg、Cr、Pb、Ni、Cu和Zn的含量，采用单因子指数法、内梅罗指数法、地质积累指数法和潜在生态危害指数法评价了重金属的积累和风险，用ArcGIS技术对重金属的空间分布进行了分析。结果表明：杨凌示范区土壤中上述8种重金属的平均含量分别为15.67、0.18、0.08、51.40、27.34、43.25、28.08、79.32 mg·kg^-1，除Hg和Cr外，其余重金属的平均含量均超过陕西关中塿土背景值，说明其在土壤中有一定累积；但8种重金属的平均含量均低于土壤环境质量农用地土壤污染风险管控标准规定的风险筛选值。Cd和Cr的点位超标率分别为10.98%和3.05%，其他重金属均未超标。所有土壤样品中As、Cr、Hg、Pb、Ni、Cu、Zn的潜在生态危害指数Eⁱ_r均低于40，为轻度风险。土壤样品中Cd的Eⁱ_r值范围为0.00～49.00，平均值为22.76±7.60，有3.66%的土壤样品中Cd含量达到轻度生态危害。农作物中上述8种重金属含量均值分别为0.016、0.019、0.005、0.108、0.033、0.090、4.880、29.272 mg·kg^-1，均低于我国食物中污染物的卫生限量标准。在谷物、蔬菜和水果内,同一种重金属的含量无显著差异，作物的重金属污染指数MPI为0.11。重金属的内梅罗指数为0.89，达到警戒水平范围；潜在生态危害综合指数RI=36.5，存在轻度生态危害。这些研究结果表明，杨凌示范区的农田土壤整体仍处于清洁安全水平，属于应予优先保护类土地。

Ecological risk assessment of soil heavy metals in Guanzhong Plain: a case study in Yangling Demonstration Area

The content of heavy metals As, Cd, Hg, Cr, Pb, Ni, Cu and Zn in 164 soil samples and 88 main crop samples from Yangling farmland were determined, and the accumulation of heavy metals was analyzed and evaluated by single factor index, Nemero index, geoaccumulation index and potential ecological hazards index. The spatial distribution of heavy metals was analyzed using ArcGIS software. The average contents of the above eight heavy metals in the soil samples were 15.67, 0.18, 0.08, 51.40, 27.34, 43.25, 28.08 mg·kg^-1 and 79.32 mg·kg^-1, respectively. Except for Hg and Cr, the average contents of all the other heavy metals exceeded the background values for Lou soil in the Guanzhong region of Shaanxi Province. The average contents of all eight heavy metals were below the soil pollution risk screening value of agricultural land. Sample exceeding rates of Cd and Cr were 10.98% and 3.05%, respectively.Other metals did not exceed control value. Potential ecological hazards indexes Eⁱ_r of As, Cr, Hg, Pb, Ni, Cu and Zn in all soil samples were lower than 40, which was a slight risk. Eⁱ_r values of Cd in soil samples ranged from 0.00 to 49.00, and the average value was 22.76±7.60. The soil numbers for Cd in moderate potential ecological risks were 3.66%. The average values of the above\|mentioned eight heavy metals in crops were 0.016, 0.019, 0.005, 0.108, 0.033, 0.090, 4.880 mg·kg^-1 and 29.272 mg·kg^-1, respectively, which were lower than the national food hygiene standard limit. There was no significant difference in the content of the same metal were found in grains, vegetables, and fruits, and the heavy metal pollution index MPI of the crop was 0.11. Nemero index for eight heavy metals was 0.89,meaning a warning range. Comprehensive potential ecological risk index RI=36.5, meant a slight ecological risk. Results of the research showed that the overall farmland soil in Yangling Demonstration Zone was still at a clean and safe level and belonged to the category of land that should be prioritized for protection.