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Aggregation kinetics of UV irradiated nanoplastics in aquatic environments

Water Research 2019 214 citations

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Researchers compared the aggregation behavior of fresh versus UV-aged polystyrene nanoplastics under various aquatic conditions. They found that UV aging altered the surface chemistry of nanoplastics, making them more stable in water and less likely to aggregate, which means they could remain suspended and bioavailable for longer periods. The study suggests that weathered nanoplastics may behave very differently from fresh particles in the environment, complicating risk assessments.

Polymers

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.

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