天津市典型河网区沉积物中重金属分布及生态风险评价

选择天津市典型河网区为研究对象,分析了沉积物中6种重金属(Cr、Cu、Mn、Ni、Pb和Zn)的分布特征,并采用富集系数法和潜在生态危害指数法分析了重金属的来源,进而评价了其生态风险。结果表明,表层沉积物中Cr、Cu、Mn、Ni、Pb和Zn的平均含量分别是58.18、23.52、524.60、22.93、25.24和49.51 mg/kg,其中Cr、Mn和Ni含量均低于天津市土壤背景值,而Cu、Pb和Zn含量在部分样点高于背景值;在垂直分布上,沉积物中Cr和Ni的含量相对稳定,而Cu、Mn、Pb和Zn的含量从底层到表层均先增加后降低。重金属富集系数(EF)分析显示,河网区表层沉积物中Cu和Zn在个别样点以及Pb在近一半样点存在人为输入过程(EF1.5),与接纳上游及区域的生活污水、农田退水有关,而Cr、Mn和Ni均来自自然源。重金属综合潜在生态危害指数(RI)评价表明,整个河网区表层沉积物为轻微生态危害水平,对区域的水环境质量不构成威胁。

Heavy metal distribution and ecological risk assessment in sediments of river network region, Tianjin City

The river network region of Tianjin City was selected for researching on heavy metal (Cr, Cu, Mn, Ni, Pb and Zn) distribution in the sediments, and enrichment factor (EF) was calculated to trace sources, then the ecology risk was assessed using potential ecological risk (RI) index. The results showed that average contents of Cr, Cu, Mn, Ni, Pb and Zn in the surface sediments were 58.18, 23.52, 524.60, 22.93, 25.24 and 49.51 mg/kg, respectively. The contents of Cr, Mn and Ni were lower than the soil background values of Tianjin City at all sites, but the contents of Cu, Pb and Zn were higher than the values at some sites. Most metal contents (Cu, Mn, Pb and Zn) increased firstly and then decreased from substrate to surface sediments. EF values of those metals revealed that Cu and Zn at one site and Pb at about half sites were effluent from anthropogenic activities (domestic sewage and irrigation return flow), and Cr, Mn and Ni were all from crustal materials or natural weathering processes. The RI index due to Cr, Cu, Mn, Ni, Pb and Zn in the surface sediments of river network region showed low-grade degree, which posed no threat to the water environment quality.