Impact of land cover on microplastics accumulation in freshwater sediments

The fate and transport of microplastic pollution in freshwater environments is a concern because of the transport of large masses of plastic to marine environments and the potential for exposure of living organisms, including humans. However, limited studies have described the temporal accumulation of plastic in freshwater sediments that may help to describe any changes in microplastic discharges over time. Here, we aimed to explore microplastic distribution in freshwater sediments and the impact of land cover type on microplastics within watersheds. Four sediment cores were collected from depositional environments in four different watersheds in Pennsylvania, United States, representing a range of land uses. We also collected synoptic surficial grab sediment samples along a 30 km stretch of one watershed both upstream and downstream of a sediment core to observe longitudinal microplastic distribution. Sediment cores were sectioned and measured radioisotope dating to establish an age model. Microplastics were then extracted, quantified, and identified based on morphology under a stereomicroscope. Microplastics were categorized as four different morphological types including fiber, fragment, film, and pellet. ArcGIS was used to determine land cover and population density within the watershed. Temporal microplastic distribution showed varying patterns in terms of concentration and morphology versus sediment depth (and age) among the locations. Interestingly, microplastic concentrations in these sediment cores were not correlated to the percentage of urban areas and population density within the watershed. Instead, the highest microplastic contamination was found in the watershed with the highest open water land cover, indicating the potential for atmospheric transport of microplastics. Also see: https://micro2024.sciencesconf.org/559029/document