Ultraviolet radiation and shear-driven micro- and nanoplastic transformation: environmental behaviour, fate and ecotoxicity—A critical review

Weathering-driven (e.g., photodegradation, mechanical degradation, and biodegradation) micro- and nanoplastic transformations reshape their behaviour, fate, and ecotoxicological effects. This review synthesized advances in ultraviolet-radiation- and shear-driven micro- and nanoplastic degradation and transformation. We integrated findings on plastic fragmentation, release of secondary micro- and nanoplastics, and physicochemical alteration under ultraviolet-shear sources from different lamps, conditions, devices, and equipment. Ultraviolet radiation photo-oxidize plastic surfaces by forming oxygenated groups (e.g., carbonyl), embrittled polymers, released secondary micro- and nanoplastics, and made plastics vulnerable to enhanced fragmentation under shear stress. Shear could release micro- and nanoplastics via mechanical abrasion and/or hydraulic flow. Ultraviolet pre-aging could substantially amplify this effect further, releasing large quantities of micro- and nanoplastics. Furthermore, ultraviolet-shear weathering could alter surface chemistry, reduced particle size, and affected pollutant interactions, thereby potentially reshaping environmental behaviour and fate and enhancing ecotoxicological impacts (e.g., enhanced inflammation, oxidative stress, hepatotoxicity, and cell death; reduced growth and trophic transfer across taxa) of micro- and nanoplastics. However, there is a critical lack of standardized protocols for weathering, including the selection of ultraviolet lamps and doses, shear sources, and particle characterization. Integrated multi-stressor experiments, including biofouling, water-sediment interactions, and hydrodynamics in combination with realistic environmental parameters, should be included in future research. In addition, analytical assays for dissolved organic carbon that include molecular-sized nanoplastic fractions and the release of toxic chemicals under ultraviolet-shear should be incorporated. Overall, by elucidating ultraviolet-shear synergies in plastic weathering, this review addressed critical gaps in understanding photo-mechanical effects on micro- and nanoplastics degradation and transformation, behaviour, fate, and ecotoxicity.