江苏省典型区农田土壤及小麦中重金属含量与评价

Heavy metal contents and evaluation of farmland soil and wheat in typical area of Jiangsu Province

为了研究江苏省典型区地震带农田土壤和小麦中重金属的污染,在具有代表性的农田采集收获期小麦及耕层土壤,分析和评价了土壤和小麦中重金属Cu、Pb、Cd、Ni、Cr、Hg、As和Zn的含量及污染程度。结果表明,土壤样品中Cd、Zn、Pb的含量均超过江苏省土壤背景值,Cr、Cu、Ni和As分别有25.64%、97.44%、92.31%和92.31%的土壤样品中超过江苏省土壤背景值,Hg的含量均在背景值以下;与国家土壤环境质量标准(GB15618—1995)中Ⅱ级标准相比,Cd的含量均超出标准限值,其它7种重金属元素含量均在标准限值以下。土壤中重金属相关分析表明,Cd、Cu、Cr、Ni、Pb、Zn、As具有相同的来源的可能性较大,而Hg与Cd、Cu、Cr、Ni、Pb、Zn、As的来源均不相同。以NY 861—2004为评价标准,小麦籽粒Pb、Cr、Hg、Ni、As样品超标率分别为100%、58.97%、33.33%、10.26%、2.56%,Cu、Zn和Cd没有样品超标,由此可见小麦籽粒中Pb的污染最为严重。采用单因子污染指数法、综合污染指数法和Hakanson潜在生态评价指数法以国家土壤环境质量标准(GB15618—1995)和江苏省土壤背景值为参比值,对农田土壤重金属污染进行评价,结果显示,从单项污染指数来看只有Cd达到重度污染水平,其它元素均在安全范围以内,从综合污染指数来看土壤重金属污染达到中度污染水平,从潜在生态评价指数法来看,研究区域表现为很强的生态危害,并以Cd为主要污染因子。

The farmland soil was the most main place of the agricultural production, and the quality of soil was the main determinant for the quality and safety of agricultural products, thus it was important to make the quality evaluation of farmland soil before the start of agriculture production. In order to investigate the pollution situation of heavy metals in farmland soil and wheat plants in a seismic belt of typical area in Jiangsu Province, the wheat and the soil of cultivation layer were collected from representative farmlands at harvest. The contents and pollution degree of Cu, Pb, Cd, Ni, Cr, Hg, As, and Zn were analyzed and evaluated. The results showed that the contents of Cd, Zn, and Pb in all soil samples were higher than the background values of Jiangsu soil, and the contents of Cr in 25.64% soil samples, Cu in 97.44% soil samples, Ni in 92.31% soil samples, and As in 92.31% soil samples exceeded the background values of Jiangsu soil, while the content of Hg in all soil samples was under the background value of Jiangsu soil. Compared with the GradeⅡof environmental quality standard for soil （GB 15618-1995）, among the elements tested, only the content of Cd in all of the samples exceeded the standard, while all the others were under the standard. Correlation analysis indicated that several heavy metal elements including Cd, Cu, Cr, Ni, Pb, Zn and As in soil had a greater possibility to have come from the same source, however, Hg rooted in a different source from those elements mentioned above. According to the standards on Foods and Products （NY861-2004）, the proportion of wheat grain samples exceeding the standards were 100%, 58.97%, 33.33%, 10.26%, and 2.56% for Pb, Cr, Hg, Ni, and As, respectively, while Cu, Zn and Cd in samples did not exceed the standard, it was demonstrated that the element of Pb was the most serious contaminant in wheat grains. The contents of heavy metal in wheat grain were influenced by the soil heavy metal concentration and other physical and chemical properties of soil as well. It was difficult to assess the pollution situation of heavy metal in soil comprehensively using a single evaluate method. Therefore, in this study, the pollution situation of heavy metals in sampled farmland soil was evaluated against references of national standard limits and background values of Jiangsu province soil through single factor pollution index, synthesizing pollution index and Hakanson＇ potential ecological evaluation index respectively. The single pollution evaluation result showed that Cd reached severe pollution levels while the other heavy metals were in the security range. Moderate pollution occured when the method of synthesizing pollution index was used. From the potential ecological evaluation index, we found strong ecological harm in the investigated region with Cd as the main pollution factor.