Atmospheric microplastics accumulation rate in a tropical Andean glacier over a hydrological year

Microplastics (MPs), defined as plastic particles between 5 mm and 0.001 mm, are transported through the atmosphere and detected in diverse ecosystems, including remote cryospheric environments. However, their atmospheric accumulation rates remain largely unquantified. This study presents the first reconstruction of the accumulation of atmospheric MPs in a tropical Andean glacier over the course of a hydrological year, defined as the annual cycle delimited by δ¹⁸O isotope depletion rather than the calendar year. An 8-m ice core was collected from Glacier 15-α on the Antisana volcano in Ecuador and dated with δ¹⁸O values to cover this cycle. MPs were visually identified and quantified, and polymer types were determined via micro-FTIR analysis. Accumulation rates were estimated by modeling a linear correlation between concentration of MPs and core depth, where surface layers are the most recent. A total of 1762 MPs were identified in the ice core, classified as fibers and fragments. Polyethylene and polymethyl methacrylate were the most common polymers throughout the core. The accumulation rate more than doubled, rising from 140 MPs/L at the beginning to 292 MPs/L at the end. These results indicate progressive atmospheric deposition of MPs, with persistent accumulation recorded in the upper troposphere, above boundary layers where turbulent mixing and frequent Amazonian rainfall would typically remove particles. Persistent MPs in the upper troposphere underscore the atmosphere's role as both a global vector and reservoir, with wide-ranging implications for ecosystems and long-range exposure risks to humans and wildlife.