Luo Changjian, Xiong Cun, Hou Yuanzhang, Qiu Yuping
Department of Environmental Science, College of Environmental Science and Engineering, State Key Laboratory of Water Pollution Control and Green Resource Recycling, Tongji University, Shanghai 200092, PR China.
Department of Environmental Science, College of Environmental Science and Engineering, State Key Laboratory of Water Pollution Control and Green Resource Recycling, Tongji University, Shanghai 200092, PR China.
Water Res. 2025 Nov 1;286:124275. doi: 10.1016/j.watres.2025.124275. Epub 2025 Jul 21.
Understanding how the intricate components of marine environments govern the transport of nanoplastics (NPs) is crucial, as this directly influences their distribution and ecosystem exposure risk. While extensive research has been conducted on natural organic matter (NOM)-regulated micro-interfacial processes of NPs in marine environments, the synergistic effect of divalent cations, particularly magnesium ion (Mg), remains underappreciated. This study elucidates how ligand-specific NOM-Mg complexation significantly influences the transport behavior of NPs in seawater. In 35 PSU seawater, humic acid (HA) and fulvic acid (FA) increased NP surface charge, achieving ζ-potentials of -25.46 mV and -19.58 mV, as compared to -18.00 mV for pristine particles. These macromolecules maintained colloidal stability with hydrodynamic diameters (d) around 600 nm and enhanced mobility, elevating the mass percentages of effluent (M) from 26.5% to 43.9% and 35.4%, respectively. In contrast, tannic acid (TA) reduced ζ-potential to -10.33 mV, triggering severe aggregation with a d of 919 nm and diminished mobility, reducing M of 7.28%. Removing Mg mitigated HA/FA-mediated mobility enhancements, decreasing M to 29.7% and 35.6%, and restored TA-induced mobility suppression, bringing M back to 28.0%, confirming the significance role of NOM-Mg interactions. Concentration-dependent experiments indicated that HA/FA-enhanced mobility correlated with Mg and NOM levels, whereas TA-induced suppression was solely dependent on Mg levels, emphasizing the more pronounced impact of TA-Mg complexes. Mechanistically, weak binding of Mg to high-molecular-weight HA (112 kDa) and FA (79 kDa), with constants K = 0.289 and 0.697, contributed to partial charge neutralization and steric hindrance. Conversely, low-molecular-weight TA (1.9 kDa) formed strong catechol-Mg bridges (K = 3.746), inducing charge-neutral aggregates. Two-dimensional correlation Fourier-transform infrared spectroscopy (2D-COS-FTIR) and solid-state C nuclear magnetic resonance (NMR) analyses identified carboxyl/phenolic groups in HA/FA and ortho-polyphenols in TA as primary Mg binding sites, indicating that structural differences among various NOM results in distinct ligand selectivity in their interactions with Mg. Molecular dynamics simulations illustrated TA-Mg bridging dynamically induced large NP aggregates within 20 nanoseconds. These findings highlight the importance of ligand-selective NOM-Mg complexation as a critical regulator of NP fate in marine ecosystems.
了解海洋环境的复杂组成部分如何控制纳米塑料（NPs）的传输至关重要，因为这直接影响它们的分布和生态系统暴露风险。虽然已经对海洋环境中天然有机物（NOM）调节的 NPs 微界面过程进行了广泛研究，但二价阳离子，特别是镁离子（Mg）的协同作用仍未得到充分认识。本研究阐明了配体特异性的 NOM-Mg 络合如何显著影响 NPs 在海水中的传输行为。在 35 实用盐度单位（PSU）的海水中，腐殖酸（HA）和富里酸（FA）增加了 NPs 的表面电荷，ζ 电位分别达到 -25.46 mV 和 -19.58 mV，而原始颗粒的 ζ 电位为 -18.00 mV。这些大分子维持了胶体稳定性，流体动力学直径（d）约为 600 nm，并提高了迁移率，使流出物的质量百分比（M）分别从 26.5%提高到 43.9%和 35.4%。相比之下，单宁酸（TA）将 ζ 电位降低至 -10.33 mV，引发严重聚集，d 为 919 nm，迁移率降低，M 降至 7.28%。去除 Mg 减轻了 HA/FA 介导的迁移率增强，使 M 降至 29.7%和 35.6%，并恢复了 TA 诱导的迁移率抑制，使 M 回升至 28.0%，证实了 NOM-Mg 相互作用的重要作用。浓度依赖性实验表明，HA/FA 增强的迁移率与 Mg 和 NOM 水平相关，而 TA 诱导的抑制仅取决于 Mg 水平，强调了 TA-Mg 络合物的影响更为显著。从机制上讲，Mg 与高分子量 HA（112 kDa）和 FA（79 kDa）的弱结合，常数 K = 0.289 和 0.697，有助于部分电荷中和和空间位阻。相反，低分子量 TA（1.9 kDa）形成了强的邻苯二酚-Mg 桥（K = 3.746），诱导电荷中性聚集体。二维相关傅里叶变换红外光谱（2D-COS-FTIR）和固态碳核磁共振（NMR）分析确定 HA/FA 中的羧基/酚基和 TA 中的邻位多酚为主要的 Mg 结合位点,表明各种 NOM 之间的结构差异导致它们与 Mg 相互作用时具有不同的配体选择性。分子动力学模拟表明，TA-Mg 桥接在 20 纳秒内动态诱导形成大的 NPs 聚集体。这些发现突出了配体选择性的 NOM-Mg 络合作为海洋生态系统中 NPs 命运关键调节剂的重要性。
