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 (< 0.2 μm) 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 (> 300 μm), particulates 8 to 300 μm, and particulates 0.2 to 8 μm. 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 (> 8 μm). 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.

在海洋环境中，沉降颗粒物作为有效营养物和金属从富营养区清除到底栖生物的有效垂直运输剂，已经得到了广泛研究。这些颗粒由透明的外聚物，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，最后是海洋降雪（> 300μm）的各种大小的部分。随着海洋积雪在水柱中形成，聚集体周围和内部形成缺氧层，可能会形成主要发生在低氧环境中的汞（Hg）甲基化的主要环境。为了检验这一过程，从筛分过的河口海水（100μm）中，在掺有稳定同位素富集的甲基汞（CH ₃）的1 L玻璃瓶中生产了海洋聚集体。在18°C下使用辊道工作台（¹⁹⁹ Hg）和无机汞（²⁰⁰ Hg（II））。轧制期结束后，收集并分析了不同的粒度级分，包括：可见的海洋积雪（> 300μm），8至300μm的颗粒以及0.2至8μm的颗粒。颗粒分析表明，与展开处理相比，两种形式的Hg都更多地掺入海洋雪中，其中²⁰⁰ Hg（II）的掺入量大于CH ₃ ¹⁹⁹ Hg。此外，无机Hg被甲基化，而CH ₃ Hg在较大的颗粒级分（> 8μm）中被脱甲基。基于Hg（II）和CH ₃同位素组成的变化评估甲基化和脱甲基化速率汞，发现与沉积物中的甲基化率相当。这些结果表明，净Hg甲基化可发生在海洋雪中以及含氧沿海水域中较小的聚集体中，并且CH ₃ Hg的这种净形成可能是沿海和开放海洋表层环境中CH ₃ Hg的重要来源。