Semester of Graduation

Summer 2020


Master of Science (MS)


Oceanography and Coastal Sciences

Document Type



Microplastics (£5 mm) have become a persistent anthropogenic pollutant and a growing environmental concern with evidence of them being found throughout several ecosystems. In recent years, there has been a growing recognition that rivers play a major role in transporting plastics from the land to the sea. The Mississippi River is the largest river in North America, draining land populated by over 100 million people. With high numbers of microplastics found in the waters of the northern of the Gulf of Mexico, it is likely that the Mississippi River is the primary source of these plastics. This study quantifies and identifies microplastics, sizes 0.5–5.00 mm, in the lower Mississippi River, as well as documents microplastics in four species of fish from the river: bluegill (Lepomis macrochirus), flathead catfish (Pylodictis olivaris), largemouth bass (Micropterus salmoides) and shortnose gar (Lepisosteus platostomus). Microplastic concentrations (n m-3) and masses (mg m-3) measured within the river were combined with river discharge measurements to estimate the annual flux of microplastics from the lower Mississippi River, and to estimates inputs near Baton Rouge, New Orleans, and the petrochemical zone in between these two cities. Polymer composition of putative microplastic particles, both from water samples and fish, were confirmed using Fourier- transform infrared spectrometer (FTIR). The mean annual flux of microplastics out of the Mississippi River (0.5 mm–5.00 mm) is estimated to be 328 billion particles, weighting approximately 811,870 kg. Within the four species of fish there was an overall underlying trend of increasing polymer richness with distance downstream in the Mississippi River. However, distance downstream from the source did not have the same underlying positive effect on the number of fibers found within fish. Both polymer richness and fiber count varied among the four fish species. The findings of this study provide baseline data on microplastic pollution within the Mississippi River and that fish are indeed ingesting microplastics. Further research is needed to understand whether ingestion was active or incidental and what, if any adverse effects this level of ingestion has on fish health and the potential for food web transfer.

Committee Chair

Benfield, Mark

Available for download on Friday, June 23, 2023