Microplastic contamination in remote mountain lakes of the americas: a baseline assessment from Patagonia and Northern California

Plastic pollution and its effects on freshwater ecosystem function are increasingly recognized, with recent research demonstrating that even remote environments are impacted. Despite growing evidence, the relative importance of local versus large-scale transport processes in delivering microplastics (MPs) to remote mountain lakes remains poorly understood. Surface water samples were collected by net trawling in 15 remote mountain lakes, eleven in the Patagonia region of Argentina and four in Northern California, United States, and analyzed by stereomicroscopy and Raman spectroscopy for MP concentration, shape, size, color, and polymer composition. MPs (≥ 80 µm) were detected at all sites, with concentrations ranging from 0.23 to 2.79 particles m −3 (mean: 0.75 ± 0.62 particles m −3 ). No significant difference in MP concentration was observed between regions (U = 12; p = 0.215), despite contrasting socioeconomic contexts. Fibers were predominant (70%), followed by fragments (24%) and films (6%), with most particles measuring less than 1 mm and over half under 0.5 mm. Ten polymer types were identified, with polyester (PES) and polyethylene terephthalate (PET) most common, primarily as fibers. No significant relationships were found between MP concentration and watershed characteristics, proximity to urban areas, public access, or altitude. The consistent MP signature across these remote lakes, regardless of morphology, accessibility, or geographic region, suggests that diffuse, large-scale transport mechanisms such as atmospheric deposition and watershed connectivity are more influential than localized point sources in remote freshwater systems. However, certain lakes near urban infrastructure or camping areas exhibited higher MP concentrations, indicating that localized anthropogenic influences may still contribute in specific cases. These findings underscore the extensive impact of MP pollution and highlight the need for coordinated mitigation strategies at local, regional, and global scales.