College of Environment and Energy, South China University of Technology, Guangzhou, 510006, China.
College of Environment and Energy, South China University of Technology, Guangzhou, 510006, China.
Water Res. 2019 Oct 15;163:114870. doi: 10.1016/j.watres.2019.114870. Epub 2019 Jul 15.
Nanoplastics (NPs) derived from degradation of macroplastics and microplastics possess potential threat to aquatic biota and human health. Their fate and transport in aquatic systems are mainly governed by aging processes and aggregation behavior. In this study, we simulated plastic aging process using UV-irradiation and compared the aggregation kinetics of fresh versus aged polystyrene NPs (PSNPs) under aqueous conditions. The results showed that fresh PSNPs had strong negative surface charge and exhibited both reaction- and diffusion-limited aggregation regimes, in agreement with classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Divalent electrolytes were 10-15 times more effective in inducing PSNP aggregation than monovalent electrolytes. The aging process inhibited PSNP aggregation in NaCl solutions by increasing the negative charge on PSNP surface and the organic matter content in solution, while promoted PSNP aggregation in CaCl solutions due to interactions between Ca and carboxyl groups formed on aged PSNP surface. Such distinct behaviors were consistent with characterizations by contact angle measurements, potentiometric titration, total organic carbon (TOC) analysis, Fourier Transform Infrared Spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Hamaker constants obtained from DLVO fitting decreased from 3.5 × 10 J for fresh PSNPs to 1.5 × 10 J for aged PSNPs. This study indicated that UV-irradiation plays a vital role in governing the fate, transport, and potential hazards of PSNPs in aquatic environments.
纳米塑料（NPs）来源于大塑料和微塑料的降解，对水生生物和人类健康具有潜在威胁。它们在水生系统中的命运和迁移主要受老化过程和聚集行为的控制。在这项研究中，我们使用紫外线照射模拟了塑料老化过程，并比较了新鲜和老化聚苯乙烯纳米颗粒（PSNPs）在水相条件下的聚集动力学。结果表明，新鲜 PSNPs 具有强烈的负表面电荷，表现出反应和扩散限制聚集两种状态，与经典的德加古因-朗道-范威夫（DLVO）理论一致。二价电解质比一价电解质更有效地诱导 PSNP 聚集，其效果相差 10-15 倍。老化过程通过增加 PSNP 表面的负电荷和溶液中的有机物含量来抑制 NaCl 溶液中 PSNP 的聚集，而在 CaCl 溶液中则促进 PSNP 的聚集，这是由于 Ca 与老化 PSNP 表面形成的羧基之间的相互作用所致。这种明显的行为与接触角测量、电位滴定、总有机碳（TOC）分析、傅里叶变换红外光谱（FTIR）和 X 射线光电子能谱（XPS）的表征一致。从 DLVO 拟合中获得的哈马克常数从新鲜 PSNPs 的 3.5×10 J 降低到老化 PSNPs 的 1.5×10 J。这项研究表明，紫外线照射在控制 PSNPs 在水生环境中的命运、迁移和潜在危害方面起着至关重要的作用。
