Nanoplastics in aquatic environments: The hidden impact of aging on fate and toxicity

The increasing release of plastic waste into aquatic ecosystems has led to the widespread occurrence of secondary microplastics (MPs) and nanoplastics (NPs), raising significant environmental and health concerns. While the toxicological effects of pristine NPs have been well documented, the role of aging—through processes such as ultraviolet (UV) photoaging and chemical oxidation—remains largely understudied. Aging fundamentally alters the physicochemical properties of NPs, potentially affecting their aggregation behaviour, eco-corona formation, and interactions with natural organic matter (NOM) and ions in aquatic environments. These changes may drastically shift the bioavailability and toxicity of NPs, making current assessments based on pristine particles environmentally unrealistic. This review synthesises the existing literature on NP aging, exploring how it affects their fate, transport, and toxicological impact on aquatic organisms. By identifying key knowledge gaps and highlighting the need for studies that account for environmental aging, this paper offers a roadmap for future research in NP environmental risk assessment. Understanding the dynamic transformations of NPs post-aging is crucial for developing more accurate models of their long-term ecological and human health impacts.