Abstract
Microplastics (MPs), defined as plastic particles between 5 mm and 0.001 mm, are transported through the atmosphere and detected in various ecosystems, including remote cryospheric environments. However, their atmospheric accumulation rates over time 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. An 8-meter ice core was collected from Glacier 15-α on the Antisana volcano in Ecuador and dated using δ¹⁸O isotope depletion to delimit a complete hydrological year. 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 1,762 MPs were identified in the ice core, classified as fibers and fragments. Polyethylene and polymethyl methacrylate were the most common polymers found throughout the core. The accumulation rate more than doubled over the year, rising from 140 MPs/L at the beginning to 292 MPs/L at the end. These results indicate progressive atmospheric deposition of MPs throughout the year, with persistent accumulation recorded in the upper troposphere, above the boundary layers, a layer where turbulent mixing and frequent Amazonian rainfall would typically remove airborne particles. Persistent accumulation of MPs in the upper troposphere underscores the atmosphere’s role as both a global vector and reservoir of MPs, with wide-ranging implications for ecosystems and long-range exposure risks to humans and wildlife.

Keywords: Antisana, Ice core, Isotopes, Contaminants, Plastics, Environment.