Developmental toxicity of functionalized polystyrene microplastics and their inhibitory effects on fin regeneration in zebrafish

The hazardous effects of microplastics on aquatic biota have been extensively documented. However, the impact of surface functionalization on the toxicological profiles of microplastics, particularly in fish, requires further investigation. In the present study, the effects of polystyrene microplastics (50–100 nm in diameter), either non-functionalized or functionalized with carboxyl (-COOH) or amino (−NH₂) groups, on zebrafish were explored. Exposure to all three types of microplastics (0.1, 1, and 10 mg/L) resulted in developmental toxicity in zebrafish at early life stages. This included increased mortality, reduced larval body length, decreased heart rate, impaired swimming ability, as well as disruptions in redox homeostasis, nervous system development, and immune responses. Moreover, all types of microplastics (1 mg/L) inhibited the regenerative capacity of larval zebrafish after caudal fin amputation, both morphologically and functionally. This inhibition was likely due to alterations in immune response, excessive production of reactive oxygen species, and disruptions in the signaling networks that regulate fin regeneration. Among the tested microplastics, amino-modified particles generally exhibited greater developmental toxicity and stronger inhibitory effects on fin regeneration. Our findings confirm that the functionalization of microplastics plays a crucial role in their interactions with biological systems and highlight concerns regarding the potential effects of functionalization, whether intentional or resulting from natural weathering processes.