宁东基地不同燃煤电厂周边土壤5种重金属元素污染特征及生态风险

Pollution Characteristics and Ecological Assessment of Heavy Metals in Soil around Different Coal-fired Power Plants of Ningdong Base

为了解宁东基地不同燃煤电厂周边土壤重金属污染特征,采集并测定了表层土壤样品的Cr、Cd、Pb、As和Hg等5种重金属含量,分析了土壤重金属元素的含量特征、不同风向上重金属含量的分布规律,采用单因子污染指数和综合污染指数对研究区域土壤重金属污染程度进行分析,并利用潜在生态风险指数法对其生态风险进行评价。结果表明:研究区域表层土壤中上述5种重金属元素质量分数的平均值分别为52.19~63.35、0.52~0.57、22.18~26.16、5.57~10.68和0.12~0.18 mg?kg^(-1),均没有超过《国家土壤环境质量标准》(GB15618—1995)二级标准(p H>7.5)和《展览会用地土壤环境质量评价标准(暂行)》(HJ350—2007)A级标准限值,但Cd、Pb和Hg的平均值超过了宁夏土壤背景值,其中Pb含量略高于背景值,Cd和Hg含量明显超出背景值,分别是背景值的4.6~5.1和6.0~9.0倍;Cr、Cd、Pb和As含量在不同燃煤电厂不同风向上的变化无明显规律,而Hg含量呈现西北风向最小,东南风向最大的分布规律,明显受主导风向影响;经单因子污染指数和综合污染指数评价,不同燃煤电厂周边表层土壤重金属的单项和综合污染指数均小于0.7,污染水平属于"清洁"。潜在生态风险指数评价结果进一步表明,电厂周边表层土壤呈轻微生态风险。尽管不同燃煤电厂周边表层土壤受重金属污染影响较小,但Cd和Hg含量在当地积累明显,这2种重金属元素的防治应受到重点关注。

To understand the characteristics of heavy metals contamination in the soil around different coal-fired power plants of Ningdong Base,The content of five selected soil heavy metals(Cr,Cd,Pb,As and Hg)were investigated and tested.Based on the analyses,the characteristics of heavy metal content,the distribution characteristics of heavy metal content in different direction were studied.Subsequently,the pollution status and ecological risks of heavy metals in the soils of survey area were assessed by single factor pollution index,Nemerow integrated pollution index and Hankanson potential ecological risk index,to provide scientific theory basis for soil heavy metal pollution control and management around different coal-fired power plants of Ningdong Base.The results showed that average contents of Cr,Cd,Pb,As and Hg in the soils of survey area were 52.19~63.35,0.52~0.57,22.18~26.16,5.57~10.68 and 0.12~0.18 mg·kg^-1,respectively,which were all lower than the threshold values of the secondary standard(pH>7.5)of“National Environmental Quality Standard for Soil”(GB 15618-1995)and A-level standard of“Environmental Quality Standard of Exhibition Sites for Soil(interim)”(HJ350-2007).But the average content of Cd,Pb and Hg was beyond Ningxia soil background value,respectively,among them,the average content of Pb was slightly higher than the corresponding background value,while the average content of Cd and Hg was 4.6~5.1 and 6.0~9.0 times higher than the corresponding background value.The distribution characteristics of Cr,Cd,Pb and As content in different direction were not obvious.Due to the impact of dominant wind direction,the distribution characteristics of Hg content was obvious,which was to be the minimum in the northwest and the maximum in the southeast.The average single factor pollution index and integrated pollution index indicated that and the soil pollution index from different coal-fired power plants were all less than 0.7,the pollution degree of all heavy metal elements in soils were clean(safe)level.Further,the potential ecological risk index revealed that the soil of the study area was in slightly potential ecological risk.Although the soil around different coal-fired power plants of Ningdong Base had little affects from the heavy metal pollution,because of Cd and Hg content accumulation were obvious,the impact of two elements on soil environment of different coal-fired power plants should be greatly paid attention.