The plastic brain part II: new insights into micro- and nanoplastics neurotoxicity

Micro- and nanoplastics (MNPs) are ubiquitously present in the environment. As a result, human exposure is inevitable. Over the last several years, the number of studies investigating the potential neurotoxicity of MNPs has skyrocketed. Therefore, this review aimed to structurally evaluate the neurotoxic effects of MNP exposure using a predefined and reproducible search strategy across multiple databases, explicit inclusion and exclusion criteria, and structured data extraction. The analysis encompassed different particle types, sizes, concentrations, and exposure durations, including both single and co-exposures, focusing on rodent and in vitro models. The majority of rodent and in vitro studies reported significant neurotoxicity following exposure to MNPs. Studies confirm uptake and accumulation, cytotoxicity, and structural changes, but also demonstrate increased oxidative stress, neuroinflammation, as well as alterations in acetylcholinesterase (AChE) activity, neurotransmitter signaling, proliferation and differentiation processes, and neurobehavior. Several studies also investigated co-exposures with various substances, which either exacerbated of mitigated the neurotoxic effects. This emphasizes the potential role of MNPs as carriers for (environmental) pollutants. In conclusion, this review suggests that MNP exposure may be associated with neurotoxicity. Importantly, it provides potential mechanisms underlying MNP-induced neurotoxicity and highlights challenges and knowledge gaps that continue to hinder accurate hazard and risk assessment of MNPs, such as the disproportionate focus on (virgin) polystyrene particles and understudied neurotoxicity-related outcomes. This review also provides recommendations to address these challenges and knowledge gaps, and it emphasizes the importance of future research to advance understanding of MNP neurotoxicity and its risks.