三峡库区及上游表层沉积物重金属形态特征及其生态风险

研究三峡库区表层沉积物中重金属形态特征及其潜在生态风险,为制定库区重金属污染防治措施提供基础资料。2020年11月,在三峡库区流水区合江江段、回水区江津江段、静水区巴南江段和长寿江段采集21个沉积物样品,通过连续提取法对重金属Cu、Pb、Cr、Cd、As、Hg总量及形态特征进行分析。结果显示:三峡库区研究江段沉积物重金属平均含量Cr>Pb>Cu>As>Cd>Hg,其中Cu、Pb和Cd的含量高于长江流域沉积物重金属背景值,静水区江段重金属含量最高;重金属形态占比具有明显差异,研究江段Pb的铁锰结合态占比高达34.99%~43.17%,Cd的离子交换态含量最高,其在合江、江津、巴南和长寿江段沉积物重金属形态总和中的占比分别为17.41%、16.65%、20.56%和18.88%,而As、Hg、Cu和Cr的残渣态含量较高,其中Hg和Cr的残渣态占比分别超过了80%和88%;研究江段沉积物中重金属污染负荷指数PLI值和潜在生态风险指数RI值分别为0.90~1.61和112.49~245.03,其中静水区江段指数值较高。综合结果表明,静水区江段沉积物重金属污染较严重,总体处于中等污染水平,Cd和Pb是主要贡献者,其中Cd具有较大的生物可利用性和潜在生态风险。

Fraction Characteristics and Ecological Risk of Heavy Metals in Surface Sediments of Three Gorges Reservoir and the Upper Reaches

The operation of the Three Gorges Reservoir has aggravated the heavy metal pollution in the reservoir area. The biological toxicity of heavy metals mainly depend on their fraction characteristics. However, there is short of research on the fraction characteristics of heavy metals in the sediment of the reservoir area. Therefore, in November 2020, 21 sediment samples were collected from four sampling sections in the stream water area, backwater area and static water area of the Three Gorges Reservoir area. The total concentration and fraction of Cu, Pb, Cr, Cd, As and Hg were analyzed by using continuous extraction method. The results showed that the average concentration of heavy metals in sediments were in the decreasing order of Cr > Pb > Cu >As > Cd > Hg, and the contents of Cu, Pb and Cd were higher than the background values of the Yangtze River basin. Heavy metals presented spatial distribution characteristics, which was higher in static section compared with other sections. The proportion of fraction were significantly different, the proportion of Fe-Mn oxide fraction of Pb was as high as 34.99%-43.17%; Cu was mainly presented in organic fraction (14.57%-20.41%); Cd had the highest percentage exchangeable fraction, 17.41%, 16.65%, 20.56% and 18.88% in the sediments of Hejiang, Jiangjin, Banan and Changshou, respectively; the residual fractions of As, Hg and Cr were relatively high, the percentages of Hg and Cr were more than 80% and 88%, respectively. The ecological risk assessment results showed that indices for pollution load index (PLI) and the potential ecological risk index (RI) values were 0.90~1.61 and 112.49~245.03, respectively, and the index value in the static water section was higher. The comprehensive results indicated that the heavy metal pollution was serious in the sediment of static water area, being at a moderate pollution level, and Cd and Pb were the main heavy metal pollutant, which Cd was of greater bioavailability and ecological risk.