Collaborative Proposal: Unravelling the Oceanic Dimethylmercury Cycle

合作建议：解开海洋二甲基汞循环这个项目将研究二甲基汞是如何在海洋中形成和移除的。二甲基汞是一种天然存在的化合物。它被认为是当人造汞转化为一甲基汞时形成的，一种在鱼体内积累的毒素。尽管二甲基汞占海洋中汞的很大一部分，但其来源和去向尚不清楚。这项研究将使用最先进的分析、基因组和建模工具来解决这一信息差距。它还将训练研究生和本科生使用实地、实验和建模方法。研究结果将用于预测模型，以预测海洋汞循环的未来趋势。需要这些模型来评估旨在扭转单甲基汞在鱼类体内生物积累日益增加趋势的国际行动的有效性。海洋中的甲基化汞是由大气和河流输送的无机二价汞在沉积物和水柱中形成的。假定的机制是一个两步过程，首先形成单甲基汞，然后缓慢甲基化成二甲基汞。第一步，二价汞的生物甲基化成单甲基汞，在沉积物中得到了相对充分的研究，已知是由硫酸盐和铁还原细菌和产甲烷菌驱动的。水柱中单甲基汞形成的机制尚不清楚，沉积物或海水中二甲基汞形成的过程基本上是未知的。直到最近，人们还认为二甲基汞在甲基化汞和总汞（所有汞种的总和）库中所占的比例很小，在全球汞循环中无足轻重。然而，最近的测量表明，海水中的二甲基汞含量可能与其他汞种类处于相同的范围。该项目将确定与二甲基汞形成有关的生物和化学甲基化剂。此外，它还将测试不同的生物地球化学条件对二甲基汞生产的影响。研究结果将用于更新全球生物地球化学模型MIT环流模型（MITgcm）中的汞模块，并分析二甲基汞的产生和降解对单甲基汞浓度的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Collaborative Proposal: Unravelling the Oceanic Dimethylmercury CycleThis project will study how dimethylmercury is formed and removed in the oceans. Dimethylmercury is a naturally occurring compound. It is thought to be formed when man-made mercury is converted into monomethylmercury, a toxin that accumulates in fish. Despite representing a large fraction of mercury in the oceans, the origin and fate of dimethylmercury is not known. This research will use state-of-the-art analytical, genomic and modeling tools to address this information gap. It will also train graduate and undergraduate students to use field, experimental, and modeling methods. The results will be used in predictive models to forecast future trends in the oceanic mercury cycle. These models are needed to evaluate the effectiveness of international actions that seek to reverse increasing trends in the bioaccumulation of monomethylmercury in fish. Methylated mercury species in the ocean are formed in sediment and the water column from inorganic divalent mercury delivered from the atmosphere and rivers. The putative mechanism is a two-step process during which monomethylmercury is formed first, followed by slow methylation into dimethylmercury. The first step, biomethylation of divalent mercury into monomethylmercury, is relatively well-studied in sediment and known to be driven by sulfate- and iron-reducing bacteria and methanogens. The mechanism for monomethylmercury formation in the water column is less well understood, and the process of dimethylmercury formation in sediment or seawater is essentially unknown. Until recently, it was assumed that dimethylmercury represented a small enough fraction of the methylated and total mercury (the sum of all mercury species) pools to be insignificant in the global mercury cycle. Recent measurements, however, show that dimethylmercury levels in seawater can be in the same range as the other mercury species. This project will identify the biological and chemical methylating agents involved in the formation of dimethylmercury. Further, it will test the impact of varying biogeochemical conditions on dimethylmercury production. Results will be used to update the mercury module of the MIT General Circulation Model (MITgcm, a global biogeochemical model, and analyze the impacts of dimethylmercury production and degradation on monomethylmercury concentrations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.