季节性缺氧水库甲基汞的产生及其对下游水体的影响

Buildup of methyl mercury in a seasonal anoxic reservoir and impact on downstream

本文采用蒸馏-乙基化结合GC-CVAFS法对贵州红枫湖水库及其各入库和出库河流中的甲基汞时空分布和控制因素进行了研究.在春、秋、冬季节总甲基汞浓度和分布无明显时空变化,在0．053-0．333 ng／L之间.春季河流是水库甲基汞一个重要的输入源．夏季水库下层甲基汞显著升高,缺氧层最高值达0．923 ng／L.同时发现．缺氧层升高的甲基汞主要来自于水体自己产生或上层水体甲基汞的沉降,而不是来自于沉积物的释放．各季节湖水和河流样品的总甲基汞和溶解氧存在显著的负相关关系,Personal相关系数r为-0．81(n=78).在春、秋、冬季节溶解态甲基汞比例略低于颗粒态甲基汞,但在夏季,特别是缺氧层,甲基汞主要以溶解态存在．夏季河流入水经水库蓄水后,到再流出时已经富含甲基汞,出库河流中总甲基汞浓度已达到各入湖河流总甲基汞平均值的5.5倍,很明显在复季红枫湖已成为下游水体甲基汞的输入源,必将会对下游生态系统产生一定影响．

In the present study, spatial and temporal distribution of methyl mercury in Hongfeng reservoir were investigated by distillation followed by aqueous phase ethylation, precollection on a Tenax, isothermal gas chromatography and cold vapor atomic fluorescence detection. Total methyl mercury （TMeHg） concentrations have no discernible difference （0.05 to 0.33ng/L） in spring, autumn and winter. In spring, the methyl mercury in the inflows was important source of methyl mercury in reservoir. In summer, methyl mercury concentration increased significantly, and the highest value was up to 0. 923ng/L in the hypolimnion. The spatial distribution in summer suggested methylation in the water column and sedimentation of particle were responsible for the evaluated methyl mercury other than the release of sediment. There was a discernible negative relationship between methyl mercury and dissolved oxygen（r = -0. 81, n =78）. In spring, autumn and winter, the proportion of dissolved methyl mercury （DMeHg） was lower than that of particulate methyl mercury, but most of methyl mercury was dissolved in hypolimnion in summer. The outflow of reservoir was rich in methyl mercury in summer, and the value was 5.5 times high- er than that in the infows. MeHg-enriched water from anoxic hypolimnia in reservoir also was discharged and potentially transported downstream where it could affect the ecosystem below the reservoir.