Gindorf Sonja, West Johannes, Graham Andrew, Jonsson Sofi
Department of Environmental Science, Stockholm University, Sweden.
Scripps Institution of Oceanography, University of California San Diego, USA.
Environ Sci Process Impacts. 2025 Feb 19;27(2):401-411. doi: 10.1039/d4em00636d.
In surface waters, photodegradation is a major abiotic removal pathway of the neurotoxin monomethylmercury (MMHg), acting as a key control on the amounts of MMHg available for biological uptake. Different environmental factors can alter the rate of MMHg photodegradation. However, our understanding of how MMHg photodegradation pathways in complex matrixes along the land-to-ocean aquatic continuum respond to changes in salinity, dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition is incomplete. In a set of laboratory experiments combining several artificial and natural waters, we demonstrate that the interplay of DOC concentration, DOM composition, and salinity affects the photodegradation rate of MMHg. The presence of DOM was found to facilitate MMHg photodegradation, but degradation rates were not altered by varying DOC concentrations over two orders of magnitude. We found DOM composition to have a stronger effect on MMHg photodegradation rates than DOC concentration. However, at high DOC levels, where most UV radiation was lost within the first cm of the reaction vessels, lower MMHg photodegradation rates were observed. When moving from terrestrially influenced waters, characterized by a high degree of humification, towards marine conditions with a protein-rich DOM pool, MMHg photodegradation rates increased. In contrast, salinity had a stabilizing effect on MMHg. Hence, especially in systems with low salt and DOC concentrations, changes in either salinity or DOC concentration can impact the photodegradation rates of MMHg.
在地表水水体中，光降解是神经毒素一甲基汞（MMHg）的主要非生物去除途径，它对可供生物摄取的MMHg量起到关键控制作用。不同环境因素会改变MMHg的光降解速率。然而，我们对于陆地到海洋水生连续体复杂基质中MMHg光降解途径如何响应盐度、溶解有机碳（DOC）浓度和溶解有机物（DOM）组成变化的理解并不完整。在一组结合了几种人工水和天然水的实验室实验中，我们证明了DOC浓度、DOM组成和盐度之间的相互作用会影响MMHg的光降解速率。研究发现DOM的存在促进了MMHg的光降解，但在两个数量级范围内改变DOC浓度并未改变降解速率。我们发现DOM组成对MMHg光降解速率的影响比DOC浓度更强。然而，在高DOC水平下，反应容器的前1厘米内大部分紫外线辐射就已损失，此时观察到较低的MMHg光降解速率。从以高度腐殖化特征的受陆地影响水体向富含蛋白质的DOM库的海洋条件转变时，MMHg光降解速率增加。相反，盐度对MMHg有稳定作用。因此，特别是在低盐度和低DOC浓度的系统中，盐度或DOC浓度的变化都会影响MMHg的光降解速率。
