School of Environmental Science and Engineering, Tianjin University, Tianjin, 300072, China.
School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing, 100083, China.
Environ Pollut. 2022 Nov 15;313:120111. doi: 10.1016/j.envpol.2022.120111. Epub 2022 Sep 5.
As the first step of methylmercury (MeHg) entry into the aquatic food webs, MeHg uptake by phytoplankton is crucial in determining the final human MeHg exposure risks. MeHg availability to plankton is regulated by dissolved organic matter (DOM) in the water, while the extent of the impacts can vary largely based on the sources of DOM. Here, we investigated impacts of DOM sources on MeHg bioconcentration by three freshwater phytoplankton species (i.e. S. quadricauda, Chlorella sp., Microcystis elabens) in the laboratory system. We found that algae-derived DOM would prohibited the cellular MeHg bioconcentration by a percent up to 77-93%, while the soil-derived DOM didn't show similar inhibition effects. DOM characterization by the excitation‒emission matrices, Fourier transform infrared spectrum, ultra‒high performance liquid chromatography‒tandem quadrupole time of flight mass spectrometry shown that the molecular size of S-containing compound, rather than thiol concentration, has played a crucial role in regulating the MeHg uptake by phytoplankton. Climate change and increasing nutrient loadings from human activities may affect plankton growth in the freshwater, ultimately changing the DOM compositions. Impacts of these changes on cellular MeHg uptakes by phytoplankton should be emphasized when exploring the aquatic Hg cycling and evaluating their risks to human beings and wild life.
作为甲基汞（MeHg）进入水生食物网的第一步，浮游植物对 MeHg 的摄取对于确定最终人类暴露于 MeHg 的风险至关重要。水中的溶解有机物（DOM）调节着浮游生物对 MeHg 的可用性，而影响的程度可能会因 DOM 的来源而有很大差异。在这里，我们在实验室系统中研究了 DOM 来源对三种淡水浮游植物（即 S. quadricauda、Chlorella sp.、Microcystis elabens）的 MeHg 生物浓缩的影响。我们发现，藻类来源的 DOM 会抑制细胞内 MeHg 的生物浓缩，抑制率高达 77%-93%，而土壤来源的 DOM 则没有表现出类似的抑制作用。通过激发-发射矩阵、傅里叶变换红外光谱、超高效液相色谱-串联四极杆飞行时间质谱对 DOM 的特征进行了表征，结果表明，含 S 化合物的分子大小，而不是硫醇浓度，在调节浮游植物对 MeHg 的摄取方面发挥了关键作用。气候变化和人类活动增加的营养负荷可能会影响淡水中浮游生物的生长，最终改变 DOM 的组成。在探索水生汞循环和评估其对人类和野生动物的风险时，应该强调这些变化对浮游植物细胞内 MeHg 摄取的影响。
