某金矿区下游土壤基于重金属化学形态风险评价及污染源解析

为定量评价某金矿对下游土壤中重金属的污染程度，基于潜在生态危害指数法及风险评价编码法，从重金属总量及化学形态两个维度来评价土壤的生态风险，并在分析重金属的富集系数与次生态、原生态相关性基础上，应用Pb同位素比值示踪土壤重金属来源。结果显示，随着与矿区距离的增大，除Cr外土壤中重金属大致逐渐减弱。土壤重金属总体呈现低风险。Cd具有较高的单项系数(均值72.50)，但其有效态占比较低，集中在10%~17%，而Pb虽然总量较少，但具有较高的有效态占比，集中在15%~30%，Pb、Cd元素带来的潜在生态风险应重点关注。Pb、Cd、Zn次生态含量与其富集系数之间存在显著相关性，R2值分别为0.765 7、0.911 5、0.602 9，表明这三种重金属与矿区生产活动更为相关，即人为来源可能性更大，而Cu、Cr主要以自然来源为主。Pb同位素比值关系显示，土壤样品整体位于尾矿源(人为源)及成土母质(自然源)端元之间。随着与矿区距离的减小，重金属含量及可交换态大致呈现增大的趋势，206Pb/207Pb同位素比值呈现下降趋势，更偏向人为源，表明矿区生产活动对靠近矿区的土壤区域输入的重金属贡献更大，结合采样点位，矿区西北边界400 m以内区域需要重点关注。 

Risk Assessment and Pollution Source Analysis of Heavy Metals in the Downstream Soil of a Gold Mining Area

In order to quantitatively evaluate the degree of pollution of heavy metals in the downstream soil by a gold mine, based on the potential ecological hazard index method and the risk evaluation coding method, the ecological risk of the soil is evaluated from the two dimensions of total amount of heavy metals and chemical morphology, and on the basis of analyzing the correlation between the enrichment coefficient of heavy metals and the sub-ecology and the original ecology, the Pb isotope ratio is applied to trace the source of heavy metals in the soil. The results showed that with the increase of the distance from the mine, the heavy metals in the soil except Cr gradually weakened. Soil heavy metals are generally at low risk. Cd has a high single coefficient (mean value of 72.50), but its active state proportion is relatively low, concentrated in 10% to 17%, while Pb, the total amount is small, but has a higher proportion of active state, concentrated in 15% to 30%, Pb, Cd elements brought by the potential ecological risks should be paid attention to. There was a significant correlation between the sub-ecological content of Pb, Cd and Zn and their enrichment coefficients, and the R2 values were 0.765 7, 0.911 5 and 0.602 9, respectively, indicating that these three heavy metals were more related to the production activities in the mining area, that is, anthropogenic sources were more likely, while Cu and Cr were mainly based on natural sources. The Pb isotope ratio relationship showed that the soil sample as a whole was located between the tailings source (anthropogenic source) and the soil-forming matrix (natural source) terminal element. With the decrease of the distance from the mine, the heavy metal content and exchangeable state showed a generally increasing trend, and the isotope ratio of 206Pb/207Pb showed a downward trend, which was more inclined to anthropogenic sources, indicating that the production activities of the mining area contributed more to the heavy metals imported in the soil area near the mining area.