Hidden microplastic pollution in protected terrestrial ecosystems: Evidence from gray wolves and Persian leopards

Microplastics are ubiquitous pollutants with the potential to penetrate even strictly protected terrestrial ecosystems. Here, we investigate microplastic contamination in apex carnivores, gray wolves and Persian leopards, within Golestan National Park, a national park and UNESCO biosphere reserve in northeastern Iran. A total of 34 scat samples were collected opportunistically across diverse habitats and systematically confirmed using DNA metabarcoding approach to avoid misidentification. Microplastic extraction involved oxidative digestion, density separation, and microscopic examination, followed by Raman spectroscopy for polymer identification. Microplastics were detected in 79.4 % of samples, with wolves showing a significantly higher total microplastic area than leopards, despite no significant differences in particle number or average size. Identified polymers included polystyrene, polyethylene, polyethylene terephthalate and polyamide, likely originating from tire wear, packaging, synthetic textiles, and agricultural plastics. Spatial analyses revealed negative correlations between microplastic load and distance to roads and nearby villages, highlighting anthropogenic sources as primary drivers of contamination even within fully protected zones. Wolves, as generalist and more mobile predators, exhibited elevated exposure compared to the more selective leopards, indicating dietary and behavioral influences on contaminant accumulation. These findings demonstrate that protected terrestrial habitats are not immune to diffuse human-derived pollutants and emphasize the role of infrastructure and rural settlements in shaping contamination patterns. Given the parallels observed in other protected areas globally, these results underscore the need for integrated monitoring and mitigation strategies to safeguard apex carnivores and ecosystem integrity in conservation areas worldwide facing similar anthropogenic pressures.