Microplastic ingestion is positively associated with age in a freshwater salamander population

Microplastics (MPs) are widely acknowledged as ubiquitous pollutants in freshwater systems and may threaten a variety of aquatic organisms, including amphibians. Owing to their permeable skin, complex life cycles, and close association with aquatic environments, amphibians are considered effective bioindicators of environmental pollution. In this study, we investigated the occurrence and characteristics of MPs in the gastrointestinal tracts of Salamandra infraimmaculata Martens, 1885 and evaluated their relationship with age and body size (snout-vent length, SVL). We analyzed 32 individuals representing different life stages. MPs were detected in 75% of individuals, with a total of 43 particles identified. Fiber and fragment particles dominated the samples, and polyethylene terephthalate (PET), ethylene-vinyl acetate (EVA), and polyethylene (PE) were the most common polymer types. Statistical analysis revealed a strong positive correlation between MP abundance and age (Spearman r = 0.835, p < 0.001), indicating a strong age-related association. In contrast, the relationship between MP abundance and body size was comparatively weaker. These results suggest that MP ingestion in amphibians may reflect age-related differences in exposure pathways, feeding behavior, or habitat use rather than morphological differences alone. Our findings indicate that microplastic ingestion is positively associated with age in amphibians and emphasize the need to consider ontogenetic factors (age-related biological differences) when interpreting patterns of MP contamination in wildlife populations. Given the ecological role of amphibians as links between aquatic and terrestrial ecosystems, MP contamination in these organisms may have broader implications for trophic transfer and ecosystem health.