黑河金盘水库沉积物中重金属形态分布特征及潜在生态风险评价

西安市黑河金盘水库是西安市的重要供水水源地,为了解重金属污染状况,对黑河金盘水库沉积物中重金属Cd、Zn、Cr和Pb的污染特征和潜在生态风险进行了研究。用EDTA铵盐溶液单一提取法和BCR连续提取法分别研究了黑河金盘水库沉积物中Cd、Zn、Cr和Pb的生物有效性和形态分布特征。结果表明:黑河金盘水库沉积物中Cd和Cr含量分别为1.68±0.81 mg/kg和87.05±9.33 mg/kg,高于中国水库底泥重金属含量背景值。沉积物中Cd的单项潜在生态风险系数远大于其它重金属,高达100.8,具有较强的生态危害性;而其它三种重金属只显示出轻微的生态危害性,因此Cd是黑河金盘水库沉积物中重金属的潜在生态风险的主要贡献者。沉积物中Pb主要以可还原态形式存在,Cd的赋存形态除残渣态外,主要以更易从沉积物孔隙水向上覆水体释放的水溶态、可交换态形式存在。各采样点沉积物中Zn和Cr的生物有效态含量与总量之比B/T值均小于5%,潜在环境效应微弱;而Pb的B/T值在50%~60%范围内,Cd的B/T值均大于10%,最高可达76.2%。上述数据表明沉积物中Pb和Cd的生物可利用性程度较高,具有较强的潜在环境危害性。

Speciation of the Heavy Metals in the Sediments of the Jinpen Reservoir and Their Assessments of Potential Ecological Risk

The Jinpen Reservoir is the main drinking water source of Xi'an City.Research on the pollution characteristics and the assessments of the potential ecological risk of heavy metals(Cd,Zn,Cr and Pb) in the superficial sediments seems to be very necessary,and the results showed that the concentrations of Cd and Cr are 1.68±0.81mg/kg and 87.05±9.33 mg/kg,respectively,higher than the background values in lake sediments in China.The speciation and bioavailability of the heavy metals in the superficial sediments were investigated by BCR sequential extraction and EDTA single extraction,respectively.The potential ecological risk index(RI) of Cd in the superficial sediments reached 100.80,which is higher than that of other heavy metals such as Zn,Cr and Pb The highof Cd implies its high ecological risk.The sequential extraction experiment showed that the main speciation of Pb in sediments was the reducible fraction.Besides the residue fraction,Cd existed in the sediments mainly in the form of dissolvable and exchangeable fractions which could be more easily transferred from the sediments to the overlying water body.And the EDTA single extraction experiment showed that the percentage of the bioavailable fraction(B/T) of Pb and Cd in sediments was higher,within the range of 50%~60%,even up to 76.2%.The above experimental results showed the bioavailability of Pb and Cd was considerably high,thus the elements had relatively high eco-environmental risk.