石化园区周边农田土壤重金属污染分析与评价

Analysis and assessment of soil heavy metals around a petrochemical industry park

以某化工园区附近300km2区域为研究区,采用辐射状精确布点,采集表层土壤样品共计200个,以该区土壤环境自然背景值和《国家土壤环境质量标准》(GB15618-1995)二级标准值为评价标准,对土壤重金属Cd、Cr、Cu、Ni、Pb、Zn、Hg和As的污染进行了分析评价.结果表明,以自然背景值为评价标准,研究区表层土壤中Cd、Hg、Cu和Pb平均含量超过自然背景值,其中,Cd为首要污染因子;以国标二级标准为评价标准,除Cd和Hg以外的6种重金属的单项污染指数平均值均小于1,Cd仍是研究区表层土壤重金属污染的主要因子.化工区西北和西南方向农田土壤重金属含量变化表明,随着与化工区距离的增加,农田土壤中Cd、Cr、Cu、Ni、Pb、Zn和Hg的含量呈显著下降趋势.采用相关分析和主成分分析研究区内土壤中重金属的来源,主因子1和主因子2的贡献率分别为65.23%、19.93%,前者反映土壤中重金属Cd、Cr、Cu、Pb、Zn和Hg积累的差异,并主要与人类活动有关;后者体现了Ni和As的变化,主要与成土母质有关.

A total of 200 topsoil samples were collected by a GPS-based radial design over an area of 300 km^2 in the vicinity of a chemical industrial park. According to the Standard of Soil Environment Quality （GB156181995） and the background values of the soil environment in this region, heavy metal pollution by Cd, Cr, Cu, Ni, Pb, Zn, Hg and As in the soils sampled was analyzed. Results of statistical analysis indicated that the mean concentrations of heavy metals Cd, Hg, Cu and Pb exceeded their natural background values. Using National Standard （GB15618-1995） as the evaluation standard, the mean single factor pollution index of all soil samples was less than 1, with the exception of Cd and Hg. Cd concentrations in the soils from the sampled sites were higher than the environmental safety criteria according to the national soil quality standard, which suggests that Cd might be considered a dominant element causing soil heavy metal pollution in the area. With increasing distance from the industrial area, the concentrations of the heavy metals Cd, Cr, Cu, Ni, Pb, Zn and Hg progressively decreased. Principal component analysis （PCA） was applied to estimate the sources of heavy metal contamination. Two factors controlling the heavy metal variability were obtained, which accounted for 65.23% and 19.93% of the total variance. Variations of Cd, Cr, Cu, Pb, Zn and Hg levels were associated with anthropogenic activities, whereas Ni and As were controlled by the parent material in the soils.