Microplastic Contamination of the Mississippi River in Illinois: Sources, Environmental Drivers, and Risk Assessment

Microplastic pollution has become a major concern for the environment in freshwater ecosystems due to its persistence, distribution, and impacts. However, research about microplastic pollution in the Illinois portion of the Mississippi River and its tributaries is still limited. This research examined the occurrence, geographical distribution, properties, and potential sources of microplastics in the Mississippi River and its major tributaries in Illinois. Surface water samples from 24 locations were collected and examined by stereomicroscopy to detect and quantify microplastics. The relationships between microplastic levels and physicochemical and land cover variables were examined using Spearman’s rank correlation. Microplastics were identified at every sampling site, with concentrations ranging from 4.5 to 76 particles per liter (average: 25.95 ± 18.15 particles/L), and fibers comprised over 71% of the total particles. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) analysis identified four types of polymers: nylon, polystyrene, polypropylene, and high-density polyethylene. Microplastic levels exhibited a negative correlation with dissolved oxygen (ρ = −0.617) and a direct correlation with pH (ρ = 0.500). The results include fundamental data about microplastic pollution at specific sites throughout the Illinois portion of the Mississippi River and emphasize possible correlations between microplastic levels, adjacent land cover, and water quality parameters.