Microplastic pollution and amphibian health: Complex physiological effects of different microplastic types on juvenile Glandirana rugosa

Microplastics (MPs) are emerging contaminants; however, their effects on post-metamorphic amphibians remain unclear. Therefore, in this study, we aimed to examine the physiological and endocrine effects of MP on juvenile Glandirana rugosa, a semi-aquatic frog species, using polypropylene and high-density polyethylene. A cellulose-exposed group was also examined to differentiate between the physical and intrinsic effects of MPs. Mortality was significantly higher in the MP-exposed groups, particularly in the PE-exposed group. Elevated corticosterone levels indicated endocrine stress, suggesting that MPs act as physiological stressors. Based on the balance of the three antioxidant enzymes, evidence of oxidative stress was found in the MP and cellulose groups, indicating that particle ingestion triggered physiological responses. Intestinal elongation was observed in all particle-exposed groups, suggesting an adaptive mechanism to mitigate potential digestive impairments. MP accumulation patterns varied by polymer type, with polypropylene exhibiting a broad distribution. These findings highlight the physical and chemical risks of MPs and suggest that MPs exert physiological stress in addition to mechanical effects. Considering the increasing prevalence of MPs in natural habitats, their role in amphibian population decline warrants further attention. Collectively, our results underscore the importance of long-term ecological assessment and targeted conservation of amphibian populations.