The Atmosphere as a Significant and Diffuse Source of Microplastic Contamination to Terrestrial and Freshwater Systems: Data from the Finger Lakes Region of New York

The atmosphere is an understudied conduit for environmental microplastics—synthetic polymer fragments, pellets, films, and fibers less than 5 mm in diameter. Fibers derived from laundering synthetic clothing dominate microplastic contamination in terrestrial and freshwater systems. This study evaluates the atmosphere—precipitation and direct deposition—as a diffuse source of microplastic fiber contamination in Seneca Lake, NY. We collected precipitation (rain and snow) from 2021 to 2022 using a metal basin placed outside immediately before the onset of precipitation and retrieved immediately afterward. Direct deposition was collected in 2023 using metal trays placed outside for 24 consecutive precipitation-free hours. Microplastics were extracted using a glass vacuum filtration system onto a 0.45 µm Millipore filter. Filters were illuminated using a NightSea UV/royal blue light to induce fluorescence in many polymers and photographed for measurement using ImageJ. We analyzed both the number of fibers and their lengths.

In 76 precipitation events, the median flux was estimated to be 530 fibers/m²/precipitation event (range 60–6,967 fibers/m²/event). We compared nine snow events (median = 675 fibers/m²/event) with nine rain events (median = 1,543 fibers/m²/event) between 6 December 2021 and 24 March 2022. Although median values appear significantly different, large variation between events meant that a non-parametric Wilcoxon rank sum test (W = 31, p = 0.44) revealed no statistically significant difference between the number of fibers deposited in rain and snow. Median fiber length for precipitation was 0.16 mm (range 0.033–11.6 mm). For 9 sampling days with no precipitation, median microplastic deposition was 89 fibers/m²/day (range 74–338 fibers/m²/day). Median length of fibers falling directly from the atmosphere was 0.17 mm (W = 180,191, p = 0.39).

From these data we draw three primary conclusions: 1) The atmosphere, both through direct airfall and precipitation, contributes a significant microplastic burden to terrestrial and freshwater systems. 2) On average, the Finger Lakes region receives some precipitation on about one-third of days. This, combined with the much larger flux during precipitation events suggests that precipitation is the main vehicle for delivering microplastic fibers into the region’s ecosystem. And 3) similarity in fiber lengths between those falling with precipitation and those settling directly suggests that processes that lift and transport fibers control what is eventually deposited more than condensation processes within clouds.