Evaluating Cardiac Morphology and Heart Rate Alterations Induced by Pyrolysis Microplastics in Danio rerio

Plastic pollution of the environment is a burgeoning worldwide issue with MPs becoming a prominent aquatic contaminant. Plastic waste pyrolysis generates fine particulate residues with the potential to serve as MPs and produce toxic effects in aquatic life. Zebrafish (Danio rerio) are commonly employed as a vertebrate model to screen environmental toxicants because they share human-like genetics, are transparent in early life stages, and are convenient to maintain. In this research, MPs collected from a pyrolysis facility were leached out and diluted in six concentrations (control, 3.12%, 6.25%, 12.5%, 25%, and 50%) to evaluate their cardiotoxicity in zebrafish larvae. Larvae were exposed for a maximum of 96 hours post fertilization (hpf), and cardiac morphology and heart rate were monitored. Counts of heartbeat significantly declined with rising MP concentrations, from 173 beats/min (control) to 112 beats/min at the highest exposure (50%). Morphological measurements indicated concentration-related cardiac malformations including pericardial edema and constricted body morphology, with most pronounced changes occurring in the 50%, 25%, and 12.5% groups. The 3.12% group showed minimal changes similar to controls. These findings show that MPs obtained by pyrolysis could produce dose-dependent bradycardia and cardiac malformations in zebrafish larvae, which highlights the cardiotoxic hazard of pyrolysis microplastics to aquatic species.