赣南离子吸附型稀土矿区土壤重金属形态分布特征及生态风险评价

稀土矿的露天开采易造成土壤重金属污染等环境问题。已有研究表明赣南离子吸附型稀土矿区土壤存在以Cd、Pb为主的轻、中度重金属污染。常见环境质量评价以主要污染因子(如重金属总量)作为衡量污染程度的指标,仅能反映重金属的富集程度。为查明赣南稀土矿区土壤重金属的赋存状态、迁移能力以及生物有效性,本文在利用电感耦合等离子体质谱法(ICP-MS)测定土壤重金属各形态含量的基础上,采用地累积指数法、潜在生态危害指数法及RAC风险评价法对赣南稀土矿区土壤重金属的生态风险进行评价。结果表明:(1)研究区土壤重金属主要以残渣态存在,占总量的65.5%。(2)土壤样品中Cd、Pb含量平均值分别是江西省土壤背景值的1.72倍和2.14倍;流域内位于矿山下游河流沿岸农田土壤Cd的平均值、尾矿库附近农田Pb的平均值分别是土壤背景值的2.33倍和3.06倍,22.7%样品的Cd或Pb含量超过风险筛选值,其中可交换态所占比例仅次于残渣态,分别占总量的47.1%和13.5%。(3)地累积指数与潜在生态风险评价结果表明Cd、Pb累积程度及生态风险水平较高,Co、Ni、Cu、Zn较低;RAC风险评价结果显示Cd生态风险较高,Co、Zn、Pb生态风险中等,Cu、Ni生态风险低。(4)针对矿区农田土壤的三种评价方法各有侧重,其评价结果异中有同,均表明研究区土壤Cd具有较高的污染程度和迁移活性,生态风险较高。本研究结果将为识别稀土矿周边农田土壤的潜在环境风险,提出有效的防范、应急与减缓措施提供科学依据。

Forms Distribution of Heavy Metals and Their Ecological Risk Evaluation in Soils of Ion Adsorption Type in the Rare Earth Mining Area of Southern Jiangxi, China

BACKGROUND: The open-pit mining of rare earth mines easily causes heavy metal pollution problems. Studies have shown that the soil of the rare earth mining area in southern Jiangxi has been polluted by heavy metals of Cd and Pb in low and moderate degrees. Environmental quality assessment usually uses pollution factors (total heavy metal content) as indicators of the degree of pollution, which can only reflect the degree of enrichment of heavy metals.
OBJECTIVES: To investigate the forms of heavy metals in the soil of the rare earth mining area in southern Jiangxi Province, migration ability and bioavailability.
METHODS: Based on the forms analysis of soil heavy metals measured by inductively coupled plasma-mass spectrometry (ICP-MS), the ecological risk of soil heavy metals in the rare earth mining area was evaluated using the geoaccumulation index method, potential ecological hazard index method and RAC risk assessment.
RESULTS: The heavy metals in the soil in the study area mainly existed in the residual form, accounting for 65.5% of the total. The average content of Cd and Pb in the soil samples was 1.72 times and 2.14 times the soil background value of Jiangxi Province, respectively. The average value of Cd in the soil in the farmland along the river downstream of the mine and the average value of Pb in the farmland near the tailing pond were 2.33 times and 3.06 times background value, respectively. The Cd or Pb content of the 22.7% samples exceeded the risk screening value. Among them, the exchangeable form of Cd and Pb accounted for 47.1% and 13.5% of the total amount, respectively, secondary to the residual form. Geoaccumulation index and potential ecological risk assessment results show that the accumulation degree and ecological risk level of Cd and Pb were higher, and Co, Ni, Cu, and Zn were lower. RAC risk assessment results show that Cd ecological risk was higher, whereas Co, Zn, and Pb was medium and Cu and Ni was low. Although the focal point and some results of the three evaluation methods were also different, the comprehensive conclusion showed that the soil Cd pollution and migration activities in the mining area were high, and the ecological risk was high.
CONCLUSIONS: The research results provide scientific basis for identifying the potential environmental risks of farmland soil in rare earth mining areas and propose effective prevention, emergency response and mitigation procedures.