老工业园土壤六价铬分布、迁移及风险研究

Distribution,Migration Law and Risk Assessment of Hexavalent Chromium in Soil:a Case Study in an Old Industrial Park

为探究成都市某老旧工业园区六价铬的空间分布、迁移规律及风险评估,该研究采集研究区域25个土壤样品,基于GIS的克里金插值法对六价铬空间分布进行可视化处理,采用吸附和土柱试验对其吸附及迁移特征进行分析,并根据地累计指数法、潜在生态风险指数法和健康风险模型对土壤六价铬的风险进行评估。结果表明,土壤六价铬的污染主要集中在研究区域的电镀行业附近,最大浓度为49.3 mg/kg,为《土壤环境质量建设用地土壤污染风险管控标准》(GB 36600-2018)中六价铬二类用地筛选值5.7 mg/kg的8.65倍。采用线性等温吸附方程、Langmuir方程和Freundlich方程拟合土壤对六价铬的吸附曲线发现,其拟合相关系数分别为0.989、0.955、0.987;线性等温吸附方程更符合六价铬的吸附动态,吸附系数K_(d)为0.0063,表明土壤对六价铬具有良好吸附作用。以原状土按照1∶1填充,进行13 d浸出试验发现,随着时间推移,出水中六价铬浓度较低,且均未超过《地下水质量标准》(GB/T 14848-2017)中的Ⅲ类标准中六价铬的标准值0.05 mg/L,表明六价铬的迁移流动性较弱。研究区域最大地累积指数达到2.606,表明六价铬高浓度区域呈现中强度污染;平均潜在生态风险指数和最大潜在生态风险指数分别为1.425和17.298,健康风险模型结果均<1,表明该区的潜在生态风险等级和人体健康风险等级低。综上,电镀铬行业电镀液的渗漏是引起区域六价铬污染的主要原因,但其对地下水威胁较小,整体来说六价铬造成的风险较小。

This study collected 25 soil samples in an old industrial park in Chengdu to investigate the spatial distribution,migration law,and risk of hexavalent chromium(Cr(Ⅵ)),and visualized the spatial distribution of hexavalent chromium using GIS Kriging interpolation method.An adsorption experiment and a column migration experiment were used to investigate the chromium adsorption kinetics and migration characteristics.Finally,the local cumulative index method,possible ecological risk index method,and health risk model were used to assess the risk of hexavalent chromium in the area.The soil in the area where the electroplating factory was located had the highest chromium concentration,with a maximum of 49.3 mg/kg,above the Cr(Ⅵ)risk screening value of the Soil Environmental Quality Soil Pollution Risk Control Standards for Construction Land(GB 36600-2018)(5.7 mg/kg).The concentration was 8.65 times higher than the previous record of 5.7 mg/kg.The Cr(Ⅵ)adsorption kinetic was described using the linear isothermal adsorption equation,the Langmuir equation,and the Freundlich equation,with correlation coefficients of 0.989,0.955,and 0.987,respectively.The linear isothermal model was found to be the most appropriate for describing kinetics,with an adsorption coefficient K_(d)of 0.0063,indicating that soil has a high Cr(Ⅵ)adsorption capacity.For 13 days,the soil was placed in a polymethyl methacrylate column to measure the Cr(Ⅵ)concentration in the leach.The data revealed that the Cr(Ⅵ)content in the leach decreased over time and that the chromium concentration did not exceed the standard value,indicating that Cr(Ⅵ)mobility was low.The research area’s maximum cumulative index was 2.606,suggesting medium-intensity pollution.The maximum potential ecological danger index was 17.298 and the average potential ecological risk index was 1.425.The health risk model’s value was less than 1.These results indicated that the potential ecological risk and human health risk in this area were low.To sum up,the leakage of electroplating solution in electroplating industry was the main reason for Cr(Ⅵ)pollution,while it had little threat to groundwater.The ecological risk of Cr(Ⅵ)in this area was low.