燃煤电厂周边土壤重金属污染特征及评价

Characteristics and evaluation of heavy metal pollution in soil around coal-fired power plants

  • 摘要: 《全国土壤污染状况调查公报》显示,全国土壤环境表现总体不容乐观,部分地区土壤污染较重,耕地土壤环境质量堪忧。为了解与评价燃煤电厂周边土壤重金属的污染状况,按照点源扇形布点原则,在电厂A和电厂B周边4个方位不同距离布设采样点,以远离电厂区域为对照点,共采集32个土壤样品,检测了Cr、Mn、Ni、Cu、Zn、As、Se、Ag、Cd、Sb、Hg和Pb等12种重金属浓度。结果表明:在2个电厂周边土壤中Mn、Ni、Cu、Zn、As、Se、Ag和Cd等8种重金属平均浓度高于安徽省土壤背景值;2个电厂周边土壤中Cd的平均浓度分别为0.230和0.172 mg/kg,与GB 15618—2018《农用地土壤污染风险管控标准》pH为6.5~≤7.5时的风险筛选值相比,平均超标倍数分别为1.79和1.49倍,最大超标点分别位于主导风下风向45°夹角500 m处和次主导风下风向500 m处;2个电厂常年主导风下风向土壤中Cr和Cd浓度高于对照点(P分别为0.03和0.04);电厂周边Cr、Cd、Ni、As、Pb和Sb等重金属存在明显空间分布差异,符合点源分布特征,其他重金属分布均匀性较好,差异不明显;2个电厂周边土壤重金属的内梅罗污染指数(PI)分别为2.7~5.0和1.5~2.4,电厂A污染程度为重度污染,电厂B为中度或轻度污染;2个电厂周边土壤重金属综合潜在生态危害指数(RI)分别为105.0~190.7和82.1~139.6,潜在生态危害为中等或轻微,Cd、Hg和As对RI的贡献较大。综合考虑电厂周边土壤中各重金属浓度和空间分布特征以及相关性分析和聚类分析结果,电厂A周边土壤中重金属可能受人类活动的影响,其污染程度和潜在生态危害整体上高于电厂B和对照点,且污染也是多方位的,不仅局限于下风向。因此对燃煤电厂监管中,应综合考虑其多方位对环境土壤和人群产生的影响。

     

    Abstract: According to the National Soil Pollution Status Survey Report, the overall soil environment in China was not optimistic. In some areas, soil pollution was heavy, and the quality of cultivated soil environment was worrying. In order to investigate and evaluate the pollution levels of heavy metals in the soil around the coal-fired power plants, according to the sector layout principle for point sources, the sampling sites were laid out at four different distances around the power plants A and B, with the area far away from the power plants was taken as the control point. A total of 32 soil samples were finally collected. The contents of 12 heavy metals such as Cr, Mn, Ni, Cu, Zn, As, Se, Ag, Cd, Sb, Hg, and Pb were analyzed. The results showed that 8 kinds of heavy metal elements including Mn, Ni, Cu, Zn, As, Se, Ag, and Cd in the soil around the two power plants were higher than the average background value of Anhui Province. The average concentration of Cd in the soil around power plants A and B was 0.230 and 0.172 mg/kg, respectively. Compared with the risk screening values under 6.5Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018), the average concentration was 1.79 and 1.49 times higher than the standard value, respectively, and the maximum over-standard points were located at 500 m downwind of 45° angle to the dominant wind and 500 m downwind of the sub-dominant wind direction. The contents of Cr and Cd in the downwind direction of its perennial dominant wind were higher than that of the control points, and the difference was statistically significant (P was 0.03 and 0.04 respectively). The heavy metal elements of Cr, Cd, Ni, As, Pb and Sb around the power plants had obvious spatial distribution differences, which were consistent with the point source distribution characteristics, while the distribution of other heavy metals was uniform, and the difference was not obvious. The pollution degree of heavy metal elements in the soil around power plant A was severe pollution, while that of power plant B was moderate or light pollution, with Nemerow comprehensive pollution index (PI) being 2.7-5.0 and 1.5-2.4, respectively for plants A and B. The comprehensive potential ecological risk index (RI) of various heavy metals around power plants A and B was 105.0-190.7 and 82.1-139.6, respectively, and the potential ecological risk was moderate or slight. The contribution rate of Cd, Hg and As to RI was large. Comprehensively considering the content and spatial distribution characteristics of heavy metals in the soil around the power plants and the results of correlation analysis and cluster analysis, the heavy metal elements in the soil around power plant A may have been affected by human activities, as the pollution degree and potential ecological risk of heavy metals in the soil were significantly higher than that of power plant B and the control points. The pollution orientation was also multi-faceted, not only limited to the downwind direction. Therefore, in the supervision of coal-fired power plants, comprehensive consideration should be given to their impact of various aspects on the environment, soil and population.

     

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