Decadal changes in microplastic accumulation in freshwater sediments: Evaluating influencing factors

Microplastics are small plastic particles with sizes ranging between 1 μm and 5 mm. Microplastics can originate from macro plastics and degrade to a smaller size or be produced directly by manufacturers. Few studies have examined microplastic contamination in freshwater sediment cores to estimate changes in microplastic contamination over time. We present the results of a study that examined sediment cores from four watersheds, Kiskiminetas River, Blacklick Creek, Raystown Lake, and Darby Creek, in Pennsylvania, USA to reveal the history of microplastic accumulation and factors that contribute to microplastic distribution. The abundance and morphology of microplastics varied over time and between these four locations. The highest microplastic abundance was found in Raystown Lake, ranging from 704 to 5397 particles kg⁻¹ with fiber as the dominant microplastic type, while Darby Creek (0–3000 particles kg⁻¹), Kiskiminetas River (0–448 particles kg⁻¹), and Blacklick Creek (0–156 particles kg⁻¹) had lower microplastic concentration. Moreover, Darby Creek had the most diverse microplastic morphology and a trend of decreasing concentration with depth. Although the Darby Creek watershed has the most developed area and highest population density, it did not have the highest microplastic concentration. Averaged over the four cores, microplastic abundance increased as global plastics production increased from the 1950s–2010s. Our findings provide insights into the fate and transport of microplastic contamination in freshwater environments, which is vital to establishing sustainable mitigation strategies.