Co-exposure of polyethylene terephthalate micro- and nanoplastics with per- and polyfluoroalkyl substances triggers immune dysregulation, apoptotic activation, and neurotoxicity.

Polyethylene terephthalate micro- and nanoplastics (PET-MNPs) and perfluorooctanoic acid (PFOA) are prevalent and environmentally persistent substances that have been identified in drinking water, food, and biological tissues. PET-MNPs may act as vectors for PFOA, potentially enhancing its toxicity, and thus applicable to environmental and human health. Although PET-MNPs and PFOA toxicity has been examined separately, few studies have looked at their combined effects. This study investigates developmental toxicity related to PET-MNP and PFOA co-exposures in zebrafish larvae exposed to the environmentally relevant concentrations of 250 µg/L (low) and 2.5 mg/L (high) PET-MNPs, and 20 µg/L (low) and 200 µg/L (high) PFOA. The combined exposure caused a dose-dependent buildup of PET-MNPs in the digestive tract, liver and pancreas, demonstrating systemic bioavailability. Due to the toxicity, oxidative stress biomarker levels (ROS, lipid peroxidation) were elevated, resulting in cellular apoptosis and an inflammatory cascade (Sudan Black B, Neutral Red staining), with macrophage and granulocyte infiltration. Neurobehavioral deficiencies (hypolocomotion, anxiety-like behavior) were correlated with acetylcholinesterase (AchE) inhibition and neuronal apoptosis. Lipid accumulation (Oil Red O stain) and hematological aberrations (o-Dianisidine stain) indicated metabolic dysregulations, vascular insult, erythropoietic dissociation. Gene expression results showed upregulation of pro-inflammatory (nfkb, il-1b), apoptotic (caspase3, p53, fas) and anti-apoptotic (bcl2), and metabolic (opa1, PPAR-a) genes, and downregulation of antioxidant (sod1, cat, GPx, gstp1) and neuroprotective (ache) markers demonstrating additive toxicity. Overall, these findings identify molecular pathways associated with exposure to PET-MNPs and PFOA concurrently, showing that oxidative stress-induced immune dysregulation and apoptosis likely contributes to larval toxicity associated with exposure.