Chapter 15: Adverse Outcome Phenomena and Toxicity Mechanisms of Micro and Nanoplastics in Human Health

The ubiquitous presence of micro and nanoplastics (MNPs) in the environment has become a pressing global concern, particularly regarding the potential impacts on human health. This review underscores the urgent need for an integrative research framework that bridges the gap between epidemiological observations and toxicological insights. Human exposure to MNPs occurs predominantly through ingestion, inhalation and dermal contact pathways. Epidemiological findings have consistently demonstrated the presence of MNPs in diverse human tissues, signaling a broad exposure and emphasizing the imperative to explore potential health risks. Population surveys have shown that the concentration of MNPs in the feces of people using disposable plastic tableware reaches 24.65 items/g. These results are associated with changes in microbiota composition and metabolite levels relevant to central nervous system disorders, energy metabolism and inflammatory responses. The detectable abundance of MNPs in the nasal mucus of individuals wearing N95 masks was measured to be 10:6 ± 2:3 items/mg. Moreover, population-based studies have linked MNP exposure to adverse health outcomes, suggesting correlation relationships between exposure levels and specific diseases such as inflammatory bowel disease (IBD) and human pulmonary ground-glass nodules (GGN). These associations underscore the necessity for in-depth toxicological investigations to elucidate the toxicity mechanisms of MNPs. Meanwhile, laboratory-based toxicological studies have the potential to reveal causative relationships and various in vitro and in vivo models have been used to explore the mechanisms of the toxicity of MNPs in the gastrointestinal tract, lungs and cardiovascular system. However, early studies failed to reflect on the complexity of the real environment. To foster interdisciplinary collaborations, this paper aims to reconcile the disparities between exposure risks and human health impacts. By critically reviewing recent advancements in understanding the exposure risks of MNPs, epidemiological observations and organ-specific toxicity, this work furnishes a comprehensive perspective on the health implications of MNPs.