Microplastic aging processes: Environmental relevance and analytical implications

The analysis of microplastics (MPs) in terrestrial environments and the evaluation of their environmental risk has gained great attention, owing to the increasing evidence for their widespread presence in soils and freshwater sediments globally. Once in the environment, MPs undergo abiotic and biotic processes which alter their properties and integrity: this process is called aging and has implications for the fate of these contaminants, their morphology and surface chemistry. Aging may also affect the analytical assessment of MPs in environmental samples which likely contain aged MPs. In contrast, analytical methods are established using pristine plastics for validation. This can lead to uncertainties in quantification and characterization. This critical review summarizes the current trends in the simulation and characterization of MP aging in laboratory conditions, highlighting limitations and knowledge gaps. It also discusses the challenges in MP analysis induced by aging in environmental samples, providing directions toward possible solutions.