From particle size to brain function: a zebrafish-based review of micro/nanoplastic-induced neurobehavioral toxicity and mechanistic pathways

Micro- and nanoplastics (MPs/NPs) are emerging neurotoxicants in aquatic environments, with increasing evidence linking their presence to behavioral impairments and molecular disruption in fish. Zebrafish (Danio rerio), a key vertebrate model, have demonstrated a range of neurobehavioral effects following MP/NP exposure, including altered locomotion, anxiety-like responses, disrupted circadian activity, and impaired social interaction. Neurotoxicity appears to be strongly size-dependent: NPs, capable of crossing the blood-brain barrier, induce direct neuronal damage primarily via oxidative stress and neurotransmitter imbalance, whereas larger particles exert indirect effects through systemic inflammation and gut-brain axis perturbation. Key neurochemical alterations, such as changes in acetylcholinesterase, dopamine, gamma-aminobutyric acid, and serotonin, are consistently associated with behavioral phenotypes. These outcomes are further modulated by exposure concentration, particle chemistry, and interactions with environmental co-contaminants. While mechanistic insights are expanding, most studies rely on simplified laboratory conditions that lack environmental realism and cross-species relevance. To advance ecological risk assessment, future research must adopt integrated, multi-level approaches that reflect real-world exposure scenarios and link mechanistic pathways to functional neurobehavioral outcomes. © 2025 The Royal Society of Chemistry.