呼伦湖水-沉积物系统中重金属的含量特征

Distribution of Heavy Metals in Water-Sediment System of Hulun Lake, China

以呼伦湖水-沉积物系统为研究对象,采用Tessier连续提取法,开展了表层沉积物中Cu、Pb、Zn、Cd的形态分析研究,系统分析了上覆水、上覆过滤水和孔隙水中重金属的浓度。研究结果表明:呼伦湖表层沉积物孔隙水中Cu、Pb、Zn和Cd的平均含量分别是上覆过滤水中的4.79、1.02、2.18倍和2.08倍,孔隙水中Cu、Zn和Cd的含量均高于上覆过滤水,揭示Cu、Zn和Cd,特别是Cu有从孔隙水向上覆水扩散迁移的明显特性;呼伦湖上覆水中的重金属均有结合在悬浮颗粒物上的趋势,揭示呼伦湖悬浮颗粒物对水环境中的Cu、Zn和Cd具有较强的自净能力,对Pb具有极强的自净能力。Cu、Zn与Pb、Cd相比较,后者较前者有在碳酸盐结合态和可交换态等次生相中富集的明显倾向;Cd在次生相中分布的百分比明显比Cu、Zn、Pb偏高;当环境条件,特别是p H发生变化时,呼伦湖表层沉积物中,Cd、Pb具有较大的生态风险。据此认为,保持呼伦湖水的偏碱性状态对湖泊的水体环境健康和生态安全至关重要。

In this work, the Tessier sequential extraction method was selected to extract Cu, Pb, Zn and Cd forms in the surface sediments from Hulun Lake, China. Concentrations of Cu, Pb, Zn and Cd in the overlying water and its filtrate and the pore water were also determined.The results showed that the average concentrations of Cu, Pb, Zn and Cd in the pore water were 4.79, 1.02, 2.18 times and 2.08 times as much as those in the filtered water, respectively. This revealed that Zn and Cd, especially Cu had a remarkable migration from the pore water to the overlying water. Higher heavy metals in the overlying water than in the filtrate indicated that heavy metals were combined with suspended particulars, implying the role of the suspended particulars to self-purify Cu, Zn and Cd, especially Pb, in lake water. Compared with Cu and Zn, the carbonates and exchangeable forms of Pb and Cd had tended to enrich in secondary phases. The percentage of Cd in the secondary phase is higher than the other three heavy metals. Cadmium and Pb in the surface sediments might have high ecological risk when environmental conditions especially p H changes. Our results suggest that keeping a weakly alkaline condition of lake water is critical to health and ecological safety of Hulun Lake.