Neurological effects induced by micro- and nanoplastics in fish: a systematic review and meta-analysis

Plastic is considered an inert material with high durability and minimal to virtually no decomposition. However, when released into the environment, they can degrade into very small particles, forming micro- and nanoplastic particles (MNP). This systematic review and meta-analysis synthesized the evidence from controlled preclinical studies to investigate the neurological effects of MNPs in fish. Following a pre-registered protocol, we searched PubMed, Web of Science, and Scopus for studies exposing fish to virgin MNPs under controlled conditions, reporting behavioral or neurochemical outcomes relevant to central nervous system function. Data were synthesized using a hierarchical random-effects model with robust variance estimation. Fifty-nine studies, comprising 723 comparisons across 13 behavioral and neurochemical outcomes, were included in the meta-analysis. The analysis accounted for correlated effect sizes within shared control groups; and nested identifiers for study, control group, and effect size. Results indicated high heterogeneity and no consistent effect of the MNP exposure on behavioral or neurochemical parameters, except for reduced traveled distance in sensory-motor assays. Meta-regression examined whether developmental stage, exposure duration, and MNP size or concentration moderate these effects. No significant moderators were identified, except for catalase activity, where longer exposure reduced enzyme activity in larvae. The findings should be interpreted with caution, as reporting quality was generally low, with key methodological details often omitted. Additionally, publication bias was found for several outcomes, and influential case analyses revealed that a few studies disproportionately affected the overall estimates. Further studies are needed to clarify the impact of MNPs on fish neurobiology and behavior.