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.