渭河西咸段表层沉积物重金属赋存形态及风险评价

Speciation and risk assessment of heavy metals in the surface sediment of the Xi'an-Xianyang section of Weihe River

以渭河西咸段表层沉积物及其孔隙水为研究对象,采用ICPMS测定了As、Cd、Cr、Cu、Pb和Zn的含量,应用改进BCR法分析了沉积物重金属的赋存形态特征,基于风险评价编码法(RAC)和潜在生态风险指数法(PERI)评价了表层沉积物重金属的生态风险。结果表明:渭河西咸段表层沉积物已受到多种重金属的复合污染,孔隙水中As和Cd质量浓度在部分断面超过US EPA水生生物水质基准的持续基准质量浓度,表层沉积物中Cd质量比在所有断面、其余重金属质量比在部分断面超过其对应陕西省A层土壤背景值;表层沉积物重金属赋存形态各异,Cd主要存在于酸可溶态中,Pb主要存在于可还原态中,Cu、As和Cr主要存在于残渣态中,Zn在酸可溶态和残渣态上均有较高的比例,以残渣态为主;RAC评价显示,As和Cu处于低风险级或中风险级,Cd处于高风险级或极高风险级,Cr、Pb均为低风险级,Zn在低风险级和高风险级之间变化;RI评价显示,各断面处于轻微至极强生态风险,Cd处于较强至极强生态风险,其余重金属均属于轻微生态风险。

The paper is aimed at presenting a report of its investigation and analysis of the regional impact of heavy metal contaminations of Weihe River in the Xi＇an-Xianyang section,in terms of concentrations of As,Cd,Cr,Cu,Pb and Zn in the surface sediments and interstitial water via the ICP-MS and the fractions of the above mentioned six heavy metals in the surface sediments by way of the modified BCR sequential extraction procedure.The results of our investigation and analysis show that the surface sediments of the River in the given section have been contaminated by the aforementioned heavy metals,for the content of such heavy metals in all or at least over 30% of the sampling section have been found beyond layer A soil background standard values of Shaanxi provincial organ in charge of the affairs.And,in terms of the concentrations of As and Cd in the interstitial water,the situation is even worse than the criterion continuous concentration（CCC） for the aquatic life surviving criteria by the US EPA in the several sampling sections.And,naturally,the situation means a potential chronic toxic risk for the aquatic ecosystem of the river,Cd,for example,one of the mainly toxic heavy metals due to its soluble form in the acid solution,and,Pb,as the reduced toxic form.Whereas Cu,As and Cr can mainly be left over with the residual fraction in the sediments,Zn has mainly been found existing in the residual fraction,letting a certain proportion remain in the acid soluble faction in the surface sediment of the river.Therefore,it is also necessary to assess the ecological risk of the heavy metals in the surface sediment by way of the risk assessment code（RAC） and the potential ecological risk index（PERI）.According to the RAC assessment,Cd pollution ranks a higher level in the risk for exhibiting high to serious risk to the region,which is followed by As and Cu,both showing low or moderate risk.While the risk of Cr and Pb bring about a lower level,both posing low risk at all sampling cross-sections,but Zn bringing about a varying risk levels between low risk and high risk.