Behavioral toxicity and neurotoxic mechanisms of PLA-PBAT biodegradable microplastics in zebrafish

Escalation of ecological concern due to biodegradable plastics has attracted the attention of many contemporary researchers. This study searched to investigate the acute and sub-chronic toxicity of polylactic acid (PLA) and polybutyleneadipate-co-terephthalate (PLA-PBAT) bio-microplastics on 3-month-old zebrafish to elucidate their potential toxic mechanisms. Acute toxicity assessments revealed 96 h-LC50 value of 12.69 mg/L for PLA-PBAT. Sub-chronic exposure of over 21 days revealed deviations in critical behavioral patterns and physiological indicators. In treated groups, weight gain and specific growth rates were significantly lower than those obtained for the control group, such that high doses induced significant reductions in total organ coefficient (p < 0.05). A positive correlation was observed between zebrafish mortality and increased doses. Detailed behavioral evaluations revealed a dose-dependent decrease in the speed and range of swimming, along with modifications in shoaling behavior, anxiety-like responses, and avoidance behaviors. Brain tissues transcriptomic analyses revealed the molecular responses underlying sub-chronic exposure to PLA-PBAT. Totally 702 DEGs and 5 KEGG pathways were significantly identified in low-dose group, with the top 2 significant pathways being ribosome pathway and cytokine-cytokine receptor interaction pathway. Totally 650 DEGs and 5 KEGG pathways were significantly identified in medium-dose group, with the top 2 significant pathways being Herpes simplex virus 1 infection pathway and complement and coagulation cascades pathway. Totally 1778 DEGs and 16 KEGG pathways were significantly identified in high-dose group, with the top 2 significant pathways being metabolism of xenobiotics by cytochrome P450 and drug metabolism - cytochrome P450 pathway. Most significantly enriched pathways are associated with immune responses. The validation of key gene in cytokine-cytokine receptor interaction pathway also confirmed its high correlation with behavioral indicators. These results indicate that PLA-PBAT is likely to cause behavioral abnormalities in zebrafish by triggering immune dysregulation in the brain.