官厅水库典型入库河流(洋河)表层沉积物重金属赋存形态特征

官厅水库曾是北京市重要的饮用水源地之一,洋河作为官厅水库重要入库河流,沉积物污染直接影响水库的水质安全.以洋河水系表层沉积物为研究对象,利用BCR三步连续提取法分析沉积物中Cd、Cr、Cu、Ni、Pb和Zn形态特征,并基于重金属形态的评价方法(次生相原生相分布比值法-RSP和风险评估指数法-RAC),评价了洋河水系表层沉积物中重金属的污染程度与风险水平.结果表明,在整体研究区域,6种重金属均以残渣态(B4态)为主,在次生相中(除B4以外的其他3种形态),Cd、Cu、Ni、Pb和Zn均以可还原态(B2态)为主,Cr以可氧化态(B3态)为主.在空间分布上,Cd在干流中游段和支流清水河段以B2态为主;Zn在干流中游段以B2态和弱酸提取态(B1态)为主,在支流清水河段以B2态为主.RSP结果表明,洋河水系表层沉积物中Cd和Zn为轻度污染,Cr、Ni、Cu和Pb无污染.但Cd和Zn在支流清水河段均为重度污染等级,其可能主要来源于区域化工原料及化学品制造行业.RAC结果表明,整体上洋河水系表层沉积物中Cd和Zn对水环境构成中等风险,Ni和Cu构成了低风险,而Cr和Pb基本无风险.

Heavy metal speciation in the surface sediments of Yang River System (Guanting Reservoir)

Guanting Reservoir (GR) is one of the most important drinking water sources in Beijing, while the sediment contamination of Yang River (an important input river of GR) may directly affect the water quality of GR. In this paper, the surface sediments of Yang River System were selected to evaluate the pollution and risk of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) based on their speciation, including ratio of secondary phase to primary phase (RSP) and risk assessment code (RAC). The results showed that all the six metals in the surface sediments of study area were dominated by B4 (residual) fraction. In the secondary phase, Cd, Cu, Ni, Pb and Zn were all dominated by B2 (reducible) fraction, and Cr was dominated by B3 (oxidizable) fraction. Spatially, Cd was mainly distributed in B2 fraction both in the middle reach of mainstream and Qingshui River (QR, a tributary of Yang River), while Zn was mainly distributed in B2 and B1 (exchangeable/acid soluble) fractions in the middle reach, but B2 fraction in QR. The RSP showed that the studied sediments were slightly polluted by Cd and Zn in whole study area, but heavily in QR, which may be due to the industries of chemical raw materials and chemicals. The RAC shows that Cd and Zn in the studied sediments posed a medium risk to the water environment, Ni and Cu posed low risk, while Cr and Pb posed no risk.