Spatiotemporal heterogeneity of microplastics and river hydrology in the Upper Mississippi River

Abstract

Microplastic pollution in surface waters of Pool 8 of the Upper Mississippi River (UMR) was investigated during May through November 2024. During this study, a total of 97 water samples (100L) were collected from sites in the main navigation channel, and backwater habitats. Overall, 932 microplastic particles were identified, ranging from 0-80 particles per sample (0.00-0.871 particles/L) and microplastic prevalence exhibited an inverse relationship with particle size. Microplastic concentrations were lower in October when discharge was lowest compared to July when discharge was highest (p<0.001) and positive correlations were found between microplastic concentration and discharge relative to habitat (p<0.05). In addition, a positive correlation was identified between microplastic concentration and turbidity in October (p<0.05). Microplastic concentrations were not significantly influenced by habitat type or distance from main channel (p>0.05). The predominant microplastic particle type identified across samples was fibers. A random subsample of particles (n=155) was verified via FTIR Spectroscopy to verify polymer types and revealed polyester, polyethylene, and polypropylene as the most common polymers. This research confirms microplastic presence in UMR Pool 8 and highlights the influence of temporal and hydrological factors on microplastic concentrations.