Experimental degradation of polystyrene via three-dimensional surface texture analysis after UV radiation and mechanical abrasion

Secondary microplastics, produced from the degradation of macroplastics, have detrimental effects on marine ecosystems, wildlife and potentially human health. Investigations into the role of degradation processes-such as ultraviolet (UV) irradiation and mechanical abrasion (MA) during water transport-in the formation of microplastics often rely on optical or scanning electron microscopy. However, these methods are inherently qualitative and do not yield detailed insights into the precise mechanisms or rates by which macroplastics degrade into smaller fragments. Here, we subjected polystyrene coffee stirrers, a disposable 'everyday plastic', to degradation treatments comprising UV and/or MA via water transport and performed quantitative analysis of the micron-scale three-dimensional plastic surface textures to investigate how disposable plastics degrade. We found that stirrers subjected to MA via simulated fluvial transport exhibited higher mass losses than stirrers subjected to non-MA treatments. We also found that stirrers subjected to MA had the most modified surface textures, characterised by 'sanded down' surfaces with fewer and smaller elevated features and more numerous valley-like features. Furthermore, we found evidence of interactive effects between degradation processes as this 'sanding down' was more pronounced in stirrers that were pre-exposed to UV before being subjected to MA. This study highlights how disposable plastics can degrade and the need for reducing everyday plastic use and their entry into aquatic environments.