贡嘎山东坡土壤重金属质量比的初步分析及风险评价

对贡嘎山东坡土壤中Cd、Pb、Cr、Ni、Hg和As的质量比进行测定,用单因子污染指数法和内梅罗综合污染指数法对其进行风险评价。结果表明:研究区表层土壤中Hg、Pb和As质量比低于国家一级标准,属未污染等级,Cd、Cr和Ni质量比存在不同程度的超标现象,土壤被污染;Cd、Pb、Cr、Ni、Hg、As的单因子污染指数分别为1.88、0.87、1.15、1.06、0.45、0.26,对土壤的污染程度从大到小依次为Cd、Cr、Ni、Pb、Hg、As;内梅罗综合污染指数PN为0.92～4.89,都属于不安全级别,其中22.2%的土壤属尚清洁等级,66.7%的土壤属轻度污染,11.1%的土壤属严重污染。

Preliminary analysis and risk evaluation of heavy metals in soil from eastern slope of Gongga Mountain

The present paper is aimed at reporting our collection and determining the concentrations of Cd,Pb,Cr,Ni,Hg and As in soils of the eastern slope of Gongga Mountain.The results of our collection and analysis show that the mean concentrations of six heavy metals in top soil are Cr>Ni>Pb>As >Cd>Hg in degraded order.The mean concentrations of Pb,Hg and As in the top soil prove to be below the tolerance limit(grade-1 in accordance with the state standard established for testing the uncontaminated soils),though lead was found different from the mean concentrations about(30.38±7.32) mg/kg dw in the topsoil from the eastern slope of the Mountain,that is,very close to the tolerance limit.At the three sampling points of the surface layer in the Faber’s matured-fir forest, lead concentrations tends to be over the tolerance limit(43.1 mg/kg dw,41.8 mg/kg dw,35.7 mg/kg dw),and so are the mean concentrations of Cd,Cr and Ni(grade-1 in accordance with the standard set up by the state).The variation coefficient of Cd is maximal at 0.91,whereas that of Pb—minimal at 0.24.Of all the three different forest types,mean concentrations of Cd,Pb,Hg and As in the surface layer of the Faber’s matured-fir forest turns to be higher than the Faber’s Fir/Purdom Poplar(Populus purdomii) mixed forest and the Faber’s middleaged fir forest.Thus,we have found that there were significant variations with Pb,Hg and As concentrations,but not with Cd.In the mean time,the average concentrations of Cr and Ni in surface layer of the Faber’s Fir/Purdom Poplar mixed forest were significantly higher than those in the other two.Thus,it can be concluded that the distribution of heavy metals determined in soil layers at each of the three points surveyed proves to be diversified,though the degree of variation turns to be not very obvious with the mobility of Cd,Cr,As,and Hg in the soil horizon from the top-layer to deep-layer.Besides,we have also worked out the single-factor contaminant index data by analyzing the information obtained from the topsoil at each sampling point.The highest degree of topsoil contamination among all the heavy metals the most serious one comes from cadmium.The order of contamination degree due to single-factor index is found decreasing in the order of PCd>PCr>PNi>PPb>PHg>PAs,which helps to prove that the topsoil contamination on the eastern slope of the Mountain were supposed to be accumulated with the elevation of Cd and Cr and Ni.Therefore,the integrated assessment of the topsoil quality for six heavy metals through analysis indicates that the contamination index PN for all the three sites vary between 0.92 and 4.89 and the contamination degree affected by heavy metals being little and slight.