Photoaging of polystyrene microspheres causes oxidative alterations to surface physicochemistry and enhances airway epithelial toxicity

Abstract Background: Microplastics represent an emerging environmental contaminant, with large gaps in our understanding of human health impacts from the myriad types of plastics. Furthermore, environmental factors may modify the plastic chemistry, further altering the toxic potency. Ultraviolet light is an unavoidable factor for airborne microplastic particulates and a known modifier of polystyrene surface chemistry. How such modifications impact the toxicity of polystyrene microparticles is unclear. As an experimental model, we aged commercially-available polystyrene microspheres for five weeks with ultraviolet radiation, then compared the cellular responses in A549 lung cells to both pristine and irradiated particulates. Results: Photoaging altered the surface morphology of irradiated microspheres and increased the intensities of polar groups on the near-surface region of the particles as indicated by scanning electron microscopy and by fitting of high-resolution X-ray photoelectron spectroscopy C 1s spectra, respectively. Even at low concentrations (1-30 µg/ml), photoaged microspheres at 1 and 5 µm in diameter exerted more pronounced biological responses in the A549 cells than was caused by pristine microspheres. High-content imaging analysis revealed S and G2 cell cycle accumulation and morphological changes, which were also more pronounced in A549 cells treated with photoaged microspheres, and further influenced by the size, dose, and time of exposures. Polystyrene microspheres reduced intracellular barrier integrity and slowed regrowth in a wound healing assay in a manner dependent on dose, photoaging, and size of the microsphere. Conclusions: UV-photoaging enhanced the toxicity of polystyrene microspheres in A549 cells. Understanding the influence of weathering and environmental aging, along with size, shape, and chemistry, on biocompatibility of microplastics may be an essential consideration for incorporation of different plastics in products.