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Physicochemical and biological ageing processes of (micro)plastics in the environment: a multi-tiered study on polyethylene
Summary
Researchers studied how polyethylene undergoes both physicochemical and biological aging simultaneously in natural environments, finding that combined aging processes differ from each individually studied in isolation. Exposure to UV light, moisture, and microorganisms altered the plastic's surface chemistry and fragmentation pattern in ways that standard single-factor tests missed. This multi-tiered approach better reflects how microplastics actually degrade in nature.
Abstract Pollution by plastic and microplastic impacts the environment globally. Knowledge on the ageing mechanisms of plastics in natural settings is needed to understand their environmental fate and interaction with biota. The study of physicochemical and biological ageing is gaining focus in the context of the environmental sciences. However experimental research has typically assessed individual ageing processes, isolating them from a more realistic and complex environmental context where multiple factors are simultaneously at play. An over-simplistic approach can limit the comprehension of the phenomenon and prevent ranking the prevalent processes. In this study we propose a multi-tiered approach to study the environmental ageing of polyethylene plastic fragments focusing on the combined assessment of physical and biological processes, in sequence. The ageing protocol included Ultraviolet (UV) irradiation in air and in a range of water solutions, followed by a biofouling test. Changes in surface characteristics were assessed by Fourier transform infrared spectroscopy and scanning electron microscopy. UV irradiation both in air and water caused a significant increase in the density of oxidized groups on plastic surface, whereby water solution chemistry influenced the process both by modulating surface oxidation and morphology. Biofouling too, was a strong determinant of surface alterations, regardless the prior irradiation treatments. This suggests that biological-driven alterations are not affected by the level of chemical-physical ageing and may represent, in real settings, a main driver of alteration of both weathered and pristine plastics. This work highlights the potential pivotal role of biofouling as a main process of plastic ageing, providing useful technical insights for future experimental works. These results also confirms that a multi-tiered experimental approach is necessary for a complete characterization of the environmental ageing of plastics.