洞庭湖表层沉积物重金属赋存形态及生态风险评价

为深入了解洞庭湖沉积物重金属污染现状及生态风险，采用欧共体物质标准局提出的BCR提取法分析29个表层沉积物中Cd、Cr、Cu、Pb和Zn的赋存形态，并应用基于重金属形态的RSP（ratio of secondary phase and primary phase，次生相与原生相分布比值法）和RAC（风险评价指数法）评价了沉积物重金属的污染程度与生态风险.结果表明:全湖范围内，Cd主要以弱酸溶解态为主，Cr主要以残渣态和可还原态为主，Cu以残渣态和可氧化态为主，Pb以可还原态和残渣态为主，Zn以残渣态和弱酸溶解态为主；RSP评价结果显示，Cd在全湖范围表现为重度污染，Pb总体表现为中度污染，但在湘、资、沅、澧"四水"入湖口以及东洞庭湖几个采样点表现为重度污染，Cr、Cu和Zn处于轻度污染和清洁水平；RAC评价结果表明，全湖范围内5种重金属生态风险排序依次为Cd > Zn > Pb > Cu > Cr，Cd表现为高等风险，Cu、Pb和Zn表现为中等风险，而Cr表现为低等风险.研究显示，在研究沉积物重金属总量基础上进行重金属形态分析，有助于深入了解重金属对环境的危害. 

Speciation and Ecological Risk of Heavy Metals in Surface Sediments of Dongting Lake

Speciation characteristics of five heavy metals (Cd, Cr, Cu, Pb, Zn) in 29 surface sediments from Dongting Lake were analyzed using the sequential extraction procedure proposed by the community bureau of reference (BCR) to understand the pollution and risk of heavy metals in Dongting Lake. The pollution and ecological risk of the heavy metals were evaluated by the ratio of secondary phase to primary phase (RSP) and risk assessment code (RAC) based on the speciation. According to the BCR speciation analysis, Cd was dominated by acid soluble fraction, Cr was dominated by residual fraction and reducible fraction, Cu was dominated by residual fraction and oxidable fraction, Pb was dominated by reducible fraction and residual fraction, Zn was mainly distributed in residual fraction and acid soluble fraction. The RSP indicated that the sediments were heavily polluted by Cd in the whole study area, moderately polluted by Pb, but heavily in the estuaries of Xiang, Zi, Yuan and Li rivers together with someplace in East Dongting Lake. The RAC indicated that the potential ecological risk of heavy metals was in descending order of Cd > Pb > Cu > Cr > Zn in the whole lake area. Cd posed a high ecological risk to the water environment throughout the whole lake, and Cu, Pb and Zn posed medium risks in the whole area, while the ecological risk of Cr in the sample area was low. Based on the study of the total amount of heavy metals in sediments, the speciation analysis of heavy metal improved our understanding of the effects of heavy metals to the environment.