Micro- and Nanoplastic Processes: Degradation, Fragmentation, Aggregation and the Need for Environmentally Relevant Reference Materials

This chapter delves into the processes of degradation and fragmentation, which dictate the fate and impact of micro- and nanoplastics. Weathering or aging, encompassing mechanisms such as photo-oxidation, hydrolysis, and microbial degradation, leads to significant changes in the chemical and physical properties of these particles, ultimately affecting their environmental behavior. Pristine plastic particles are often studied but misrepresent the reality of plastics under prolonged environmental stress. Instead, weathered particles are of paramount importance, and suitable reference materials are still needed to validate methods and to study representative effects. This chapter will correlate laboratory studies and modeling approaches to focus on the weathered tiny plastic pollutants, highlighting their relevance in real-world scenarios. The aging of these particles also significantly impacts their aggregation behavior by modifying surface chemistry and particle interactions, which can, in turn, modify their distribution in both water and soil, thereby influencing their movement and potential ecological impacts. Given these considerations, understanding the degradation mechanisms and their influence on the behavior of micro- and nanoplastics is essential for predicting their fate and assessing their broader implications for ecosystems.