Materials science underpinnings of micro and nanoplastics

There is considerable interest in microplastics and nanoplastics (MNPL) due to their ubiquity and their potential for serious health consequences. A framework that allows us to consider all relevant aspects of MNPL requires us to enunciate (a) their formation mechanisms, their sizes, shapes, and chemical functionalities (upstream properties); and (b) their health and environmental consequences (downstream properties). In this perspective, we discuss the materials science underpinnings of MNPL formation, and the current open questions that need immediate attention from the research community. Specifically, we highlight the lack of understanding of how angstrom-level environmentally triggered bond-breaking events lead to the formation of ∼10 nm-1 mm-sized fragments. Are there universal theoretical ideas that unify MNPL formation in disparate situations? What is the role of external stressors, polymer morphology, and molecular weight? Answering these questions requires us to develop a suite of novel metrologies - from accurate, accelerated aging tests that mimic natural MNPL creation processes but speed up these rare events into the normal laboratory time scales; to the extension of standard physicochemical characterization tools which are hard to apply in the context of MNPL formation due to small sample masses.