School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin 300401, China.
Institute of Environmental Processes and Pollution Control, and School of Environment and Civil Engineering, Jiangnan University, Wuxi 214122, China.
Environ Sci Technol. 2023 Apr 25;57(16):6520-6529. doi: 10.1021/acs.est.2c09140. Epub 2023 Apr 12.
The colloidal stability of nanoplastics in aqueous solutions is greatly regulated by photoaging and dissolved organic matter (DOM). However, how the exposure order to sunlight and DOM modifies the environmental behavior of nanoplastics is seldomly determined. Here, with two different exposure orders, we investigated the impact of molecular-weight (MW)-fractionated humic acids (HAs) derived from biochar and the Suwannee River, respectively, on the aggregation of poly(ethylene terephthalate) nanoplastics (PET-NPs) in mono- and divalent electrolyte solutions. For exposure pattern (i) (photoaging followed by HA coating), photoaged PET-NPs had more oxidized surfaces and exhibited 22-320% higher binding affinity to HAs (especially the higher MW fractions) than the pristine counterparts, which greatly improved the dispersion of PET-NPs. For exposure pattern (ii) (HA coating followed by photoaging), HA-PET assemblies were formed, the dispersion of which increased with increasing irradiation time and was significantly higher than that of the samples in the exposure pattern (i) at the end of the experiment. This high dispersion of photoaged HA-PET assemblies was ascribed to the extra oxidation of PET by reactive oxygen species generated in the PET-HA interfaces during photoaging. These findings highlight the "active nature" of HA-PET assemblies, which provide new insight into the reaction of HA with nanoplastics beyond adsorption in the natural environment.
纳米塑料在水溶液中的胶体稳定性受光老化和溶解有机质（DOM）的极大调节。然而，阳光和 DOM 的暴露顺序如何改变纳米塑料的环境行为却很少被确定。在这里，我们通过两种不同的暴露顺序，研究了分别来自生物炭和苏万尼河的分子量（MW）分级腐殖酸（HA）对聚对苯二甲酸乙二醇酯纳米塑料（PET-NPs）在单和二价电解质溶液中聚集的影响。对于暴露模式（i）（光老化后 HA 涂层），光老化的 PET-NPs 具有更多的氧化表面，与 HA（特别是较高 MW 级分）的结合亲和力比原始对应物高 22-320%，这大大提高了 PET-NPs 的分散性。对于暴露模式（ii）（HA 涂层后光老化），形成了 HA-PET 组装体，其分散性随着辐照时间的增加而增加，在实验结束时，其分散性明显高于暴露模式（i）中的样品。光老化的 HA-PET 组装体的高分散性归因于在光老化过程中在 PET-HA 界面产生的活性氧物种对 PET 的额外氧化。这些发现强调了 HA-PET 组装体的“活性性质”，为天然环境中 HA 与纳米塑料的反应提供了新的见解，超出了吸附的范围。
