Behavioural impact of microplastics on zebrafish development

Abstract Microplastic (MP) pollution in aquatic environments is ubiquitous and characterized by particles of highly irregular shapes. Yet, most laboratory studies examining MP impacts on aquatic species rely on pristine polymer spheres, which poorly reflect the diversity and complexity of environmentally derived MPs. In this study, we assessed the developmental effects of environmentally relevant, household-derived, irregular microplastic fragments, on zebrafish. Fragments of synthetised MPs used in this study displayed heterogeneous sizes and jagged shapes, similar to environmental MPs fragments. Acute exposure to all MP types did not induce embryonic lethality or gross malformations but did result in significant sublethal toxicity: exposed larvae showed reduced touch-evoked escape responses, consistent with a pronounced loss or damage of lateral line neuromasts. To further characterize the underlying sensory impairment, we examined neuromast structure and function, which revealed mechanical disruption, kinocilia fusion, and reduced mitochondrial activity. Our findings emphasize that physical and physicochemical interactions associated with fragment morphology and polymer type drive neurosensory toxicity than particle size alone. This work highlights that acute MP exposure disrupts key sensory behaviours and structures critical for ecological fitness. Overall, these results support the need for increased regulatory and scientific attention to behavioural and sensory endpoints in microplastic risk assessments.