School of Engineering and Applied Sciences, Harvard University, Cambridge Massachusetts 02138, USA.
Environ Sci Technol. 2010 Mar 1;44(5):1698-704. doi: 10.1021/es9032524.
Methylmercury (MeHg) bioaccumulation in marine food webs poses risks to fish-consuming populations and wildlife. Here we develop and test an estuarine mercury cycling model for a coastal embayment of the Bay of Fundy, Canada. Mass budget calculations reveal that MeHg fluxes into sediments from settling solids exceed losses from sediment-to-water diffusion and resuspension. Although measured methylation rates in benthic sediments are high, rapid demethylation results in negligible net in situ production of MeHg. These results suggest that inflowing fluvial and tidal waters, rather than coastal sediments, are the dominant MeHg sources for pelagic marine food webs in this region. Model simulations show water column MeHg concentrations peaked in the 1960s and declined by almost 40% by the year 2000. Water column MeHg concentrations respond rapidly to changes in mercury inputs, reaching 95% of steady state in approximately 2 months. Thus, MeHg concentrations in pelagic organisms can be expected to respond rapidly to mercury loading reductions achieved through regulatory controls. In contrast, MeHg concentrations in sediments have steadily increased since the onset of industrialization despite recent decreases in total mercury loading. Benthic food web MeHg concentrations are likely to continue to increase over the next several decades at present-day mercury emissions levels because the deep active sediment layer in this system contains a large amount of legacy mercury and requires hundreds of years to reach steady state with inputs.
甲基汞（MeHg）在海洋食物网中的生物积累对食用鱼类的人群和野生动物构成了风险。在这里，我们为加拿大芬迪湾的一个沿海港湾开发并测试了一个河口汞循环模型。质量预算计算表明，从沉降固体进入沉积物的 MeHg 通量超过了从沉积物到水的扩散和再悬浮的损失。尽管在底栖沉积物中测量到的甲基化速率很高，但快速的脱甲基作用导致 MeHg 的净原位产生可忽略不计。这些结果表明，对于该地区的浮游海洋食物网而言，流入的河流和潮汐水而不是沿海沉积物是 MeHg 的主要来源。模型模拟表明，水柱中的 MeHg 浓度在 20 世纪 60 年代达到峰值，并在 2000 年下降了近 40%。水柱中的 MeHg 浓度对汞输入的变化反应迅速，大约在 2 个月内达到稳定状态的 95%。因此，预计通过监管控制实现汞负荷减少后，浮游生物体内的 MeHg 浓度将迅速响应。相比之下，尽管总汞负荷最近有所下降，但自工业化开始以来，沉积物中的 MeHg 浓度一直在稳步增加。由于该系统中的深层活动沉积物层含有大量的汞遗产，并且需要数百年才能达到与输入物的稳定状态，因此在当前的汞排放水平下，底栖食物网中的 MeHg 浓度可能会在未来几十年继续增加。
