闽西南崩岗土壤重金属含量、分布、来源及生态风险

Content, distribution, source and ecological risk of heavy metals in soils of Benggang areas in Southwest Fujian

  • 摘要: 选取福建省长汀县黄泥坑崩岗群内2处典型崩岗及附近一无崩岗山坡(对照区), 采样并测定了63份0~20 cm土壤样品Cu、Zn、Ni、Pb、Cr、As、Cd含量, 运用相关分析与主成分分析进行重金属来源辨识, 并应用Hankanson潜在生态风险指数法, 以福建省背景值和国家二级标准作为参比, 对研究区重金属进行潜在生态风险评价。结果表明: 研究区土壤重金属含量从高到低的顺序依次为Zn(105.56 mg·kg-1)>Pb(67.21 mg·kg-1)> As(61.47 mg·kg-1)>Cu(22.33 mg·kg-1)>Cr(17.12 mg·kg-1)>Ni(5.24 mg·kg-1)>Cd(0.80 mg·kg-1), Pb、Cd含量表现为崩岗区>对照区, Cu、Zn、Ni、Cr、As、Cd含量与之相反。1号崩岗Zn、Pb、As和Cd平均值分别是福建省背景值的1.12倍、2.82倍、8.68倍和13.33倍, 2号崩岗这4种元素平均值分别是背景值的1.11倍、1.36倍、11.22倍和16.67倍, 对照区该4种元素平均值分别是背景值的1.58倍、1.60倍、5.14倍和14.44倍; 与国家土壤环境质量二级标准比较得出, 崩岗区和对照区As平均值分别超标1.92倍和2.70倍, Cd平均值分别超标2.31倍和2.60倍。从集水坡面到沟道末端, 崩岗区Pb、Zn、Cd含量呈增加趋势, Cu、Cr含量基本维持稳定, Ni含量有所降低; 从坡面上部到下部, 对照区Cu、Zn、Ni、Cr、Cd含量呈增加趋势, Pb含量略有降低; As含量在研究区的分布无明显变化。Cu、Ni、Cr主要来源为成土母质, Zn主要来源于禽畜养殖, Cd、As的主要来源包基岩风化稀土开采, Pb主要来源于基岩矿化、煤炭燃烧及汽车尾气排放等复合污染源。以福建省背景值为参比时, Cd潜在生态风险系数达到“极强风险”, As为“较强风险”, 其余均为“轻微风险”; 以国家二级标准为参比时, Cd属“较强风险”, 其余均为“轻微风险”。潜在生态风险指数(Ri)表现为2号崩岗>对照区>1号崩岗。研究区Cd、As污染已较为严重, 应采取相应的安全防范措施。

     

    Abstract: Sixty-three surface (0-20 cm) soil samples were collected in two typical Benggang areas (BG1 and BG2) in Huangnikeng Benggang Group and an adjacent hillside without Benggang (CK) in Changting County of southwestern Fujian Province. The contents of seven heavy metals in those samples were measured, and each heavy metal’s source was identified by means of correlation and principal component analyses. Finally, the potential ecological risks of heavy metals were assessed on the basis of soil background values of Fujian Province and the second class standard of national soil environmental quality. The results indicated that the order of contents of heavy metals in the investigated soil was Zn (105.56 mg·kg-1) > Pb (67.21 mg·kg-1) > As (61.47 mg·kg-1) > Cu (22.33 mg·kg-1) > Cr (17.12 mg·kg-1) > Ni (5.24 mg·kg-1) > Cd (0.80 mg·kg-1), the contents of Pb and Cd in both BG1 and BG2 were higher than those in CK, while those of Cu, Zn, Ni, Cr, As and Cd were opposite. The contents of Zn, Pb, As and Cd in BG1 were 1.12, 2.82, 8.68 and 13.33 times, BG2 were 1.11, 1.36, 11.22 and 16.67 times, and CK were 1.58, 1.60, 5.14 and 14.44 times the averages of soil background values in Fujian Province. Compared with the second class standard of national soil environmental quality (GB15618—1995), the contents of As in Benggangs and CK soils were 1.92 and 2.70 times, respectively, and the content of Cd was 2.31 and 2.60 times, respectively, the nation standard. From upper slope to bottom of slope in Benggang systems, the contents of Pb, Zn and Cd increased, Cu and Cr basically remained stable, while Ni decreased. From top to bottom of CK slope, Cu, Zn, Ni, Cr and Cd contents increased, and Pb content decreased slightly. As content in study region kept relatively consistent. According to heavy metals resources analysis with correlation and principal component analyses methods, Cu, Ni and Cr mainly came from parent materials, Zn was associated with livestock breeding probably, Cd and As originated from substrate weathering and mining of rare earth elements, and Pb were ascribed to compound pollution of bedrock mineralization, coal combustion, and exhaust emission on provincial highway (No. 205). The potential ecological risk coefficients of Cd and As were classified as ‘extreme strong level’ and ‘strong level’ respectively, and those of Cu, Zn, Ni, Pb, Cr were ranked as ‘slight level’ with soil background values in Fujian Province as reference; while only Cd was ranked as ‘strong level’ and others were in range of ‘slight level’, when the second class standard of national soil environmental quality was used as reference. The order of potential ecological risk index was BG2>CK>BG1. The proper measures would be suggested to control the severe contamination of Cd and As in this area.

     

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