Fulvic acids (FAs) are known to regulate the fate of mercury (Hg) in sediments, but the key effects of their properties are still unclear. In this study, field investigations and simulation experiments were conducted in a heavy metal-polluted wetland to identify FA characteristics and their association with the production and bioaccumulation of methylmercury (MeHg). Compared to permanently inundated areas (PIA), seasonally inundated areas (SIAs) had lower total Hg levels in sediments, whereas higher MeHg levels in sediments (0.20 ± 0.09 ng g⁻¹ vs. 0.55 ± 0.31 ng g⁻¹) and benthos (0.25 ± 0.22 ng g⁻¹ vs. 1.62 ± 1.78 ng g⁻¹). Meanwhile, the THg and MeHg concentrations in the same macrophyte species between PIA and SIA also followed a similar rule with benthos. FA-bound Hg in the sediment was significantly correlated with MeHg in the sediment (p < 0.01), as well as THg and MeHg in benthos (p < 0.05), indicating that FAs have the capacity to promote MeHg production and bioaccumulation. Moreover, the FAs in the sediments of the SIA had lower fractions and alkyl C/O-alkyl C ratios, but higher molecular weights and THg/MeHg concentrations than those in the PIA, indicating that FAs in SIA have increased bioavailability and enhanced competition for Hg, favoring significantly elevated FA-bound Hg levels. Biological exposure testing further demonstrated that FAs extracted from SIA had a greater ability to increase the production and bioaccumulation of MeHg than those extracted from PIA. Overall, these results highlight that the molecular composition and sources of FAs, excluding their concentrations, are one of important factors responsible for the obvious spatial heterogeneity of MeHg in sediments and aquatic organisms in the wetland.

众所周知，富里酸 (FA) 可以调节沉积物中汞 (Hg) 的归宿，但其特性的关键影响仍不清楚。在本研究中，在受重金属污染的湿地中进行了实地调查和模拟实验，以确定 FA 特征及其与甲基汞 (MeHg) 生产和生物积累的关联。与永久淹没区 (PIA) 相比，季节性淹没区 (SIA) 的沉积物中总汞含量较低，而沉积物中的甲基汞含量较高（0.20 ± 0.09 ng g ^-1与 0.55 ± 0.31 ng g ^-1）和底栖生物（ 0.25 ± 0.22 ng g ^-1与 1.62 ± 1.78 ng g ^-1）。同时，PIA 和 SIA 之间同一大型植物物种中的 THg 和 MeHg 浓度也遵循与底栖生物相似的规律。沉积物中 FA 结合的 Hg 与沉积物中的 MeHg 显着相关 ( p  < 0.01)，以及底栖生物中的 THg 和 MeHg ( p < 0.05)，表明 FA 具有促进甲基汞生产和生物积累的能力。此外，SIA 沉积物中的 FAs 具有较低的分数和烷基 C/O-烷基 C 比率，但分子量和 THg/MeHg 浓度高于 PIA，表明 SIA 中的 FAs 增加了生物利用度并增强了对Hg，有利于显着升高的 FA 结合 Hg 水平。生物暴露测试进一步表明，从 SIA 中提取的 FAs 比从 PIA 中提取的 FAs 具有更大的能力增加甲基汞的产量和生物积累。总体而言，这些结果强调了 FAs 的分子组成和来源，不包括它们的浓度，是导致湿地沉积物和水生生物中 MeHg 空间异质性明显的重要因素之一。