Influence of Hurricane Helene on Microplastic Deposition in the Mountainous Southeastern United States

Abstract

Due to climate change, we expect more intense hurricanes, leading to higher precipitation than previously observed. Historic storms, such as Hurricane Helene, that struck the southeastern United States (U.S.) in September 2024, deposited between 508 and 762 mm (20–30 in) of rainfall in rural, mountainous parts of Western North Carolina, resulting in catastrophic flooding. Less well known is the extent of microplastic (MP) deposition in these less developed areas. While there is insight into MP deposition due to typhoon events in Eastern Hemisphere, in our assessment, we conducted the first-ever study U.S. based assessment of MP deposition in a severely affected southeastern U.S. region at multiple locations (Iron Duff, Coweeta Hydrologic Laboratory (Coweeta), and Highlands Biological Station (HBS), months before (January to September), during (September), and weeks post-hurricane (October to November). Our findings show that Hurricane Helene contributed to elevated MP deposition at all sites (3 to 22x higher than pre-Hurricane Helene levels), where total storm MP deposition was 1,280, 2,179, and 10,243 MP/m² at Iron Duff, Coweeta, and HBS, respectively. This historic storm accounted for 4.2, 4.6, and 18.8% of the annual MP deposition at Iron Duff, Coweeta, and HBS, respectively. Using backward trajectory analysis, we found that air masses reaching our sampling locations differed during Hurricane Helene compared to pre- and post-Helene periods. Our regression model estimated that the total anomalous deposition over the area of the U.S. affected by Hurricane Helene (3,798,756.55 km²) was 3.85 × 10¹⁵ MPs. Polyamide, polystyrene, polyethylene terephthalate, polypropylene, and polyethylene were the main polymers detected before and during Hurricane Helene. Our findings underscore how extreme storms can produce short-term spikes in MP deposition above ambient levels in a region. Thus, highlight the need to prioritize funding and policy initiatives to better assess risks posed by MPs to vulnerable ecosystems.