松花江水体沉积物汞污染的生态风险

Ecological risk assessment of mercury pollution in the sediment of Songhua River

为了发展一种方法以便重建河流沉积物中汞的初始背景浓度,并在此基础上评价松花江汞污染现状,于2005年采集了吉林市至哈尔滨市松花江河段沉积物样品,用混合酸消解后,使用原子荧光分析测定了沉积物中总汞含量,使用ICP-MS和ICP-AES分别测定了沉积物中钪和主要阳离子含量.以保守元素钪为基准元素,重建了松花江沉积物中汞的初始背景含量,然后计算了沉积物中汞的富集比率和潜在生态风险指数.结果表明,吉林市至松源河段沉积物汞仍然存在极强的生态污染风险,松源以下河段沉积物中Hg存在中等或轻微生态污染.与以前研究多采用全球工业化前沉积物中汞最高含量或上地壳中汞平均含量来评价沉积物中汞的生态风险相比,本方法比较客观地反映了研究河段沉积物中汞的污染现状和生态风险,建议在沉积物重金属污染评价研究中采用.

Mercury is an extremely toxic metal and may cause heavy ecological risk at low concentration in environment. Thus, it has become one of the hot spots of research. The Second Songhua River was subjected to a large amount of mercury discharge from chemical industries in Jilin city in 1960s and 1970s. The objectives of this study were to develop a method to reconstruct the primitive background concentration of mercury and assess the ecological risk of mercury. The sediment was sampled from Songhua River between Jilin city and Haerbin city in 2005. Total concentration of Hg, Sc, and major cations （AI, Fe, Mg, Ca, K, Na） in the sediment was measured by atomic fluorescence spectrometer, ICP-MS, and ICP-OES, respectively, following digestion of the sediment with various acids. The primitive background concentration of mercury in the surface sediment was reconstructed employing conservative scandium. Enrich ratios and potential ecological risk index of Hg in the sediment of Songhua River was calculated, according to reconstructed the background concentrations of mercury. The measured concentration of mercury in the sediment generally decreased from 1.27 mg· kg^-1 at Jilin city of upstream to 0.01 mg·kg^-1 at Haerbin city of downstream. Mercury in the sediment of Songhua River between Jilin city and Songyuan city might cause very strong ecological risk, while downstream of Songyuan, it might not cause ecological risk. The methodology used in this study might assess more accurately the ecological risk of Hg in the sediment, compared to previous methods using maximal concentration of Hg in the global sediment before industrialization or the average concentration in the upper continental crust.