In order to understand the speciation distribution and the ecological environmental risk of heavy metals in the sediment of Dongping Lake, which is the second largest freshwater lake in Shandong Province and serves as the important reservoir in the east route of the South-to-North Water Diversion Project of China, the speciation of Cu, Ni, Pb and Zn in 44 surface sediment samples collected around Dongping Lake was analyzed by using the BCR (European Community Bureau of Reference) sequential extraction procedure. The environmental risk of heavy metals was evaluated by the ratio of secondary phase to primary phase (RSP) and risk assessment code (RAC), both of which are based on the fraction concentrations of heavy metals. The results showed that the Ni, Cu, Pb and Zn existed mainly in residual fraction (65.9%, 56.1%, 49.3% and 39.3%, respectively), and then the Fe-Mn oxide fraction was the dominant for Pb (38.2%), Cu (28.6%) and Ni (17.0%), while Zn was found mainly in the organic and sulfide fraction (34.7%). The weak acid soluble fraction accounted for the lowest percentage with the descending order of Zn (12.2%)>Cu (6.9%)>Pb (4.3%)>Ni (4.1%). The extractable fraction of heavy metals (i.e. the sum of the weak acid soluble fraction, the Fe-Mn oxide fraction and the organic and sulfide fraction) showed significant spatial variations. Both the concentrations and percentages of the extractable fraction of Cu, Ni and Pb were higher around the inflow area of River Dawen, while Zn showed high concentrations and percentages of the extractable fraction around the whole lake except in the lake central area. Different fractions of Cu, Pb and Zn had some correlations between each other. The fraction concentrations of heavy metals generally had positive correlations with the organic matter content, but were weakly correlated with the average particle size. The assessment results showed that Zn was generally at the middle pollution level, which might pose middle environmental risk, while Cu, Ni and Pb were at clean to light pollution level, which environmental risk was low.%东平湖是南水北调工程东线的主要调节湖和山东省西水东调的水源地,其水体环境状况直接关系到调水工程受水区的水质安全.为了解东平湖沉积物中重金属的形态赋存特征及其生态环境风险,采用BCR三步提取法对东平湖44个表层沉积物样品中重金属元素Cu、Ni、Pb和Zn的形态分布特征进行了分析,并运用基于重金属形态的次生相与原生相比值法(RSP)和风险评估指数法(RAC)对其环境风险进行了初步评价.结果表明,东平湖表层沉积物中4种重金属均以残渣态为主,其占总量的比例表现为:Ni(65.9%)>Cu(56.1%)>Pb(49.3%)>Zn(39.3%);Pb、Cu和Ni以Fe-Mn氧化物结合态为其次要赋存形态,其所占比例分别为38.2%、28.6%和17.0%;而Zn则以有机物及硫化物结合态为其次要赋存形态,所占比例为34.7%;弱酸提取态所占比例最小,表现为:Zn(12.2%)>Cu(6.9%)>Pb(4.3%)>Ni(4.1%).表层沉积物中可提取态重金属含量和比例的空间分布特征明显且较为一致,Cu、Ni和Pb表现为大汶河入湖区较高,Zn除湖心区略低外,其他湖区尤其是北部出湖区均较高.Cu、Pb和Zn的不同形态间存在一定相关性,且与有机质主要呈正相关,但与平均粒径的相关性较弱.评价结果表明,Zn总体表现为中度污染,具有中等环境风险;Pb为轻度污染,Cu和Ni为无污染,其环境风险均较低.
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