Environmental Science Program, Memorial University of Newfoundland, St. John's, NL A1C 5S7, Canada; Department of Earth Sciences, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada; Department of Earth and Environmental Science, Acadia University, Wolfville, NS B4P 2R6, Canada.
Environmental Science Program, Memorial University of Newfoundland, St. John's, NL A1C 5S7, Canada.
J Environ Sci (China). 2018 Jun;68:160-168. doi: 10.1016/j.jes.2018.02.025. Epub 2018 Mar 8.
Methylmercury (MeHg) bioaccumulation is a growing concern in ecosystems worldwide. The absorption of solar radiation by dissolved organic matter (DOM) and other photoreactive ligands can convert MeHg into less toxic forms of mercury through photodemethylation. In this study, spectral changes and photoreactivity of DOM were measured to assess the potential to control photoreactions and predict in situ MeHg concentration. Water samples collected from a series of lakes in southwestern Nova Scotia in June, August, and September were exposed to controlled ultraviolet-A (UV-A) radiation for up to 24hr. Dissolved organic matter photoreactivity, measured as the loss of absorbance at 350nm at constant UV-A irradiation, was positively dependent on the initial DOM concentration in lake waters (r=0.94). This relationship was consistent over time with both DOM concentration and photoreactivity increasing from summer into fall across lakes. Lake in situ MeHg concentration was positively correlated with DOM concentration and likely catchment transport in June (r=0.77) but not the other sampling months. Despite a consistent seasonal variation in both DOM and Fe, and their respective correlations with MeHg, no discernable seasonal trend in MeHg was observed. However, a 3-year dataset from the 6 study lakes revealed a positive correlation between DOM concentration and both Fe (r=0.91) and MeHg concentrations (r=0.51) suggesting a more dominant landscape mobility control on MeHg. The DOM-MeHg relationships observed in these lakes highlights the need to examine DOM photoreactivity controls on MeHg transport and availability in natural waters particularly given future climate perturbations.
甲基汞（MeHg）的生物积累是全球生态系统中日益关注的问题。溶解有机质（DOM）和其他光反应配体对太阳辐射的吸收可以通过光脱甲基作用将 MeHg 转化为毒性较低的汞形式。在这项研究中，测量了 DOM 的光谱变化和光反应性，以评估控制光反应和预测原位 MeHg 浓度的潜力。
2023 年 6 月、8 月和 9 月从新斯科舍省西南部的一系列湖泊中采集水样，在受控的紫外-A（UV-A）辐射下暴露长达 24 小时。通过在恒定的 UV-A 照射下测量 350nm 处吸光度的损失来测量 DOM 的光反应性，DOM 的光反应性与湖水中初始 DOM 浓度呈正相关（r=0.94）。
随着时间的推移，这种关系在整个湖泊中，DOM 浓度和光反应性从夏季到秋季都在增加，保持一致。湖泊原位 MeHg 浓度与 DOM 浓度呈正相关，并且在 6 月与集水区输送有关（r=0.77），但在其他采样月份则没有。尽管 DOM 和 Fe 的季节性变化一致，并且它们各自与 MeHg 相关，但未观察到 MeHg 的明显季节性趋势。
然而，来自 6 个研究湖泊的 3 年数据集显示，DOM 浓度与 Fe（r=0.91）和 MeHg 浓度（r=0.51）之间存在正相关，这表明在景观上对 MeHg 的控制更为重要。
这些湖泊中观察到的 DOM-MeHg 关系强调了需要检查 DOM 对天然水中 MeHg 迁移和可用性的光反应性控制，特别是考虑到未来的气候干扰。
