湘江沉积物重金属生态风险及释放通量研究

以湘江石峰大桥至马家河大桥区段的湘江沉积物作为研究对象,通过采集该区段表层沉积物样品,利用电感耦合等离子质谱仪（ICP-MS）和原子吸收分光光度计测定Cu、Pb、Zn、Cd、Cr、Mn、As和Hg的含量和赋存形态.结果表明,Cd和As的平均含量均超过土壤环境质量标准（GB15618-1995）三级标准限值,Mn平均含量超过我国土壤元素背景值（583mg/kg）.采用Hakanson潜在生态危害指数法评价沉积物中重金属生态风险,表明5个采样点中有4个采样点潜在生态危害综合指数均超过600,属于很强生态危害程度.最后通过连续实验研究了不同流速、不同pH值对沉积物中Cu、Zn、Cd以及Mn释放规律的影响,结果表明,增大水流速度、降低上覆水体pH值均可促进沉积物中重金属的释放,实验还发现4种重金属的释放通量都比较小,其中释放通量最大的Mn为7.50 μg/（g·d）,沉积物中重金属向水环境的释放是一个缓慢、长期的过程.

The ecological risk assessment and releasing flux estimation of heavy metal in the Xiangjiang River sediments

In this research, the Xiangjiang River areas from the Shifeng bridge to the Majiahe bridge were selected as study areas to assess the ecological risk and release amount of heavy metals in the surface sediments of the Xiangjiang River, Hunan Province, China. A sum of five surface sediment samples were collected, then the total contents and the specific chemical forms of Cu、Pb、Zn、Cd、Cr、Mn、As and Hg in these samples were measured by the inductively coupled plasma mass spectrometry (ICP-MS) and atom absorption spectrophotometer (AAS). Results showed that the average contents of Cd and As in sediments were higher than the standard of class Ⅲ of National Soil Environmental Quality Standard (GB15618-1995). Moreover, the Hakanson ecological risk index was adopted to assess the potential ecological risk of heavy metals in the surface sediments. The results showed that the comprehensive indexes of potential ecological risks (RI) for four sediment samples were higher then 600, suggesting that the Xiangjiang River has been suffered high ecological hazards. Finally, continuous experiments were carried out to study the effect of flow rate and initial pH values on the heavy metals release from sediments. The results showed that the increased flow rate and the decreased initial pH could promote the release of heavy metals in sediments, while the release amount of four heavy metals were too small and the largest release amount of Mn was 7.50μg/(g·d). It suggested that the release of heavy metals in the sediments into the water environment was a slow and long-term process.