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An examination of the factors influencing mercury and methylmercury particulate distributions methylation and demethylation rates in laboratory-generated marine snow

机译：检查影响实验室产生的海洋积雪中汞和甲基汞微粒分布甲基化和脱甲基化速率的因素

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In the marine environment, settling particulates have been widely studied for their role as effective vertical transporters of nutrients and metals scavenged from the euphotic zone to the benthos. These particulates are composed of transparent exopolymers, plankton and bacterial cells, detritus and organic matter, and form various size fractions from colloids (<0.2μm) to aggregates, and finally marine snow (>300 μm). As marine snow forms in the water column, anoxic layers form around and within the aggregation potentially creating a prime environment for the methylation of mercury (Hg), which occurs primarily in low oxygen environments. To examine this process, marine aggregates were produced from sieved estuarine seawater (100 μm) in 1-L glass bottles spiked with stable isotope enriched methylmercury (CH3199Hg) and inorganic mercury (200Hg(II)) at 18° C using a roller-table. After the rolling period, different particle-size fractions were collected and analyzed, including: visible marine snow (>300μm), particulates 8 to 300 μm, and particulates 0.2 to 8μm. Particulate analysis indicated higher incorporation of both forms of Hg into marine snow compared to unrolled treatments, with greater incorporation of 200Hg(II) than CH3199Hg. In addition, inorganic Hg was methylated and CH3Hg was demethylated in the larger particulate fractions (>8μm). Methylation and demethylation rates were assessed based on changes in isotopic composition of Hg(II) and CH3Hg, and found to be comparable to methylation rates found in sediments. These results indicate that net Hg methylation can occur in marine snow and smaller aggregates in oxic coastal waters, and that this net formation of CH3Hg may be an important source of CH3Hg in both coastal and open ocean surface environments.
机译：在海洋环境中，人们广泛地研究了沉降颗粒物，因为它们是从富营养区到底栖生物清除的营养物和金属的有效垂直运输者。这些微粒由透明的外聚物，浮游生物和细菌细胞，碎屑和有机物组成，并形成从胶体（<0.2μm）到聚集体，最后是海洋积雪（> 300μm）的各种大小分数。随着水柱中海洋雪的形成，聚集体周围和内部形成缺氧层，从而可能形成汞（Hg）甲基化的主要环境，这主要发生在低氧环境中。为了检验这一过程，在1升玻璃瓶中筛分的河口海水（100μm）产生了海洋聚集体，这些玻璃瓶中掺有稳定的富含同位素的甲基汞（CH3 199 Hg）和无机汞（ 200 <使用辊台在18°C下加热（Hg（II））。轧制期结束后，收集并分析了不同的颗粒级分，包括：可见的海洋积雪（>300μm），颗粒8至300μm和颗粒0.2至8μm。颗粒分析表明，与展开处理相比，两种形式的汞在海洋雪中的掺入率更高，而 200 Hg（II）的掺入率大于CH3 199 Hg。此外，在较大的颗粒部分（>8μm）中，无机汞被甲基化，而CH3Hg被脱甲基。基于Hg（II）和CH3Hg同位素组成的变化评估了甲基化和脱甲基化速率，发现其与沉积物中的甲基化速率相当。这些结果表明，Hg的甲基化甲基化可能发生在海洋雪中以及有氧的沿海水域中较小的聚集体中，并且CH3Hg的这种净形成可能是沿海和开放海洋表层环境中CH3Hg的重要来源。

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