Year: 2026
Type: review
Abstract: ABSTRACT Growing production and consumer use of plastics have contributed to the widespread occurrence of microplastics (MPs) in the environment – the upper size limit of MP is taken commonly as 5.0 mm. Photooxidation (PO) driven by ultraviolet (UV) radiation plays an important role in the transformation of MPs. This review summarizes the mechanisms of photooxidation under both direct UV exposure and indirect pathways and synthesizes findings from a wide range of environmental studies. Photooxidation begins when light absorption generates radicals that initiate chain reactions. Subsequent oxidation and chain scission introduce oxygen-containing functional groups, which alter crystallinity and weaken the polymer. The rate and outcome of this process depend on both the plastic formulation and its surrounding environment. Water may suppress surface oxidation by reducing UV penetration and oxygen availability, while also promoting physical fragmentation by penetrating oxidation-induced voids and facilitating crack propagation. Research evidence and field-derived carbonyl-index data for polyethylene and polypropylene indicate location-dependent aging across urban areas, agricultural soils, beaches and estuaries, and offshore surface waters. Urban and agricultural samples generally show lower median values, whereas stronger signals occur for beach polyethylene and offshore polypropylene. These patterns are descriptive rather than quantitative because the available studies are not methodologically harmonized and the environmental histories of sampled particles are largely unknown. The relationship between oxidation state and particle size distribution remains complex and is not resolved quantitatively. Based on this synthesis, future research should emphasize improved characterization of photooxidized MPs and standardized methodologies to better understand their environmental fate and implications across different compartments.
Source: Environmental Challenges
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,140
OpenAlex ID: W7212128104