作者：Yao, C., Dai, Z., Xue, J., Xiang, Y., Yin, Y., Tian, S., Jiang, T., Wang, Y., Cai, Y. & Wang, D.

Suspended particulate matter (SPM) plays a pivotal role in the transport and biogeochemical cycling of methylmercury (MeHg) in freshwater ecosystems. However, the trophic bioavailability and dominant sources of SPMassociated MeHg remain poorly characterized, limiting our understanding of its ecological impacts. This study conducted a comparative analysis of five representative freshwater systems in Southwest China, comprising three lakes and two rivers, to elucidate system-specific dynamics of SPM-associated MeHg. Results indicate that SPM contained substantially higher total MeHg concentrations and trophic-bioavailable fractions than surficial sediments. Remarkably, lake SPM accounted for 48.9% of the trophic-available MeHg in surficial sediment inventories, significantly higher than the contribution of river SPM (10.9%), underscoring the central role of lake systems as reservoirs of trophic-available MeHg and amplifiers of food web exposure. In lakes, MeHg in organicrich SPM originated predominantly from in-situ methylation and aqueous-phase adsorption, with minimal contributions from sediment resuspension. Conversely, river SPM accumulated MeHg primarily through adsorption processes, reflecting distinct source mechanisms between the two systems. These findings challenge conventional paradigms that prioritize sediment resuspension as the dominant MeHg source in freshwater SPM and highlight the critical role of water-column processes, particularly in lacustrine environments, in driving SPMassociated MeHg dynamics. Altogether, these insights have profound implications for assessing trophic transfer risks and managing Hg contamination in aquatic environments.

悬浮颗粒物（SPM）在淡水生态系统中甲基汞（MeHg）的迁移和生物地球化学循环中起着关键作用。然而，SPM结合态甲基汞的营养级生物可利用性及其主要来源仍鲜有明确表征，这限制了对其生态影响的理解。本研究对中国西南部五个代表性淡水系统（包括三个湖泊和两条河流）进行了比较分析，以阐明各系统中SPM结合态甲基汞的特异性动态。结果表明，SPM中的总甲基汞浓度和营养级生物可利用组分均显著高于表层沉积物。值得注意的是，湖泊SPM贡献了表层沉积物存量中营养级可利用甲基汞的48.9%，远高于河流SPM的贡献率（10.9%），凸显了湖泊系统作为营养级可利用甲基汞储库和食物网暴露放大器的重要作用。在湖泊中，富含有机质的SPM中的甲基汞主要来源于原位甲基化和水相吸附，沉积物再悬浮的贡献极小。相反，河流SPM主要通过吸附过程积累甲基汞，反映出两种系统之间存在不同的来源机制。这些发现挑战了将沉积物再悬浮视为淡水SPM中甲基汞主要来源的传统范式，并强调了水柱过程（尤其是在湖泊环境中）在驱动SPM结合态甲基汞动态中的关键作用。综上所述，这些见解对评估水生环境中的营养传递风险和汞污染管理具有深远意义。

（来源：Water Research 2026  DOI: 10.1016/j.watres.2025.125310）