The discovery of a pervasive subsurface methylmercury maximum in the world's oceans highlights the importance of understanding the processes and rates that produce and destroy this potent neurotoxin in seawater. Two approaches have been published in the literature, one based on the spatial distribution of mercury species in seawater and, more recently, a second approach based on seawater incubation studies using additions of isotopically enriched mercury species. The reaction rates determined by these two approaches differ by several orders of magnitude. Using Arctic Ocean seawater and the incubation approach to determine mercury methylation and demethylation rates, we observed unexplainable methylation and demethylation at time zero and poor fitting of the data to first-order kinetics. A critical analysis of previous incubation studies reveals similar deficiencies, especially when the mercury was added at low concentrations to simulate ambient seawater conditions. These findings cast doubt on the validity of mercury methylation and demethylation rates determined by the seawater incubation approach, and call for the development of alternative methods to determine these crucially important rate constants in ambient seawater.

在世界海洋中普遍存在的地下甲基汞最大值的发现凸显了了解在海水中产生和破坏这种有效神经毒素的过程和速率的重要性。文献中已经发表了两种方法，一种是基于海水中汞物种的空间分布，另一种是基于海水温育研究的第二种方法，其中使用了同位素富集的汞物种。这两种方法确定的反应速率相差几个数量级。使用北冰洋海水和孵化方法确定汞的甲基化和去甲基化速率，我们观察到在零时间不可解释的甲基化和去甲基化，并且数据与一阶动力学的拟合性很差。对以前的孵化研究进行的严格分析显示出类似的缺陷，特别是当添加低浓度的汞以模拟周围海水条件时。这些发现使人们对由海水温育方法确定的汞甲基化和脱甲基化速率的有效性产生怀疑，并呼吁开发其他方法来确定环境海水中这些至关重要的速率常数。