Assessing the embryotoxicity of polypropylene micro- and nanoplastics generated through simulated environmental weathering in zebrafish (Danio rerio)

Polypropylene (PP), a thermoplastic polymer of the polyolefin group, is among the most widely produced plastics worldwide due to its excellent physicochemical properties and versatile applications. However, improper disposal of PP and exposure to natural physicochemical and biological processes in the environment can lead to its fragmentation into smaller particles, known as PP micro- and nanoplastics (MNPs). The reduced size of these particles increases their bioavailability and, consequently, their potential interaction. In this study, PP MNPs were generated to simulate environmental weathering and fragmentation through a combination of photodegradation and mechanical degradation techniques. The resulting MNPs were used to evaluate the effects of exposure at different concentrations on morphological, functional, and behavioral parameters during the early developmental stages of zebrafish (Danio rerio). After a six-day exposure period, the findings revealed that PP MNPs accelerated hatching rates, enhanced spontaneous tail coiling (STC), accumulated on the chorion surface, and elevated maximum acceleration, total absolute turn angle, and diminished frequency of entries into the periphery. Collectively, these results indicate that exposure to PP MNPs induces early developmental and behavioral alterations in zebrafish embryos and larvae, suggesting primary toxic effects during the embryonic and larval stages.