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Microplastics in Mississippi River Fishes: A Watershed Approach
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This study examined microplastic occurrence in fish from multiple locations along the Mississippi River watershed, finding widespread contamination across species. Researchers used a watershed-scale approach to understand how microplastics enter river food webs and accumulate in freshwater fish.
Microplastics are plastic particles less than 5mm that come from different sources, such as industrial products, cosmetics, and the breakdown of the macroplastics. Microplastics derive from terrestrial sources but concentrate in flowing freshwaters where they may enter aquatic food webs. The northern Gulf of Mexico has shown very high microplastic concentrations, which are assumed to be sourced from the Mississippi River and its watershed. This study seeks to study microplastics in fish in the Mississippi River and the Gulf of Mexico. Fish stomachs and intestines from fish underwent chemical digestion, filtration, and microplastics identification and enumeration through FT-IR spectrometry. Chapter one seeks to quantify microplastics in four different fish species (Shortnose Gar Lepisosteus platostomus, Largemouth Bass Micropterus salmoides, Bluegill Lepomis macrochirus, and Flathead Catfish Pylodictis olivaris) across the Mississippi River, and test the hypothesis that microplastic counts in fish will increase from the headwaters to the mouth. Fish were sampled from several sites along the main-stem Mississippi River (from Minnesota to Louisiana). All four fish species had microplastics in their stomachs and downstream locations had higher microplastics concentrations; however, location had no significant effect on microplastic counts among species except for Largemouth Bass. Chapter two sought to quantify microplastics across body size in two common estuarine fish species, the Hardhead Catfish and Southern Flounder. Hardhead Catfish are benthic omnivores, and among one of the most common estuarine fishes in the Gulf of Mexico (but with almost no fishery value). Southern Flounder are an ambushing flatfish that inhabit estuaries at younger ages before a move offshore as adults. I hypothesized that microplastic concentrations in stomachs (and intestines) as measured by the number of microplastic particles in fish would be higher in smaller-sized fishes than larger-sized fishes (according to total length), as smaller fish target smaller prey and possibly directly ingest more microplastics. Fish were sampled in 2018 and 2019 within balanced size classes. Larger fish ingested more microplastics, which can be as a result of indirect consumption or accidental ingestion from the water column.
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Identification and Quantification of Microplastic Pollution in Water Samples and Four Species of Fish from the Mississippi River
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Microplastics were found in water samples and in four fish species from the Mississippi River, the largest North American river draining a densely populated watershed. The findings confirm that one of the world's major river systems is contaminated with microplastics, which are likely entering the Gulf of Mexico.
Microplastics in mainstem Mississippi River fishes
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Researchers found microplastics in all four fish species sampled at all five sites along the mainstem Mississippi River, with polypropylene fragments being most common and occurrence increasing in the Lower Mississippi, though only Largemouth Bass showed a clear downstream increase in microplastic load.
Microplastics in the Mississippi
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This poster study reviewed two research papers examining microplastics in the Mississippi River, finding that plastic concentrations increase downstream and in heavily populated areas, and that fish throughout the river system ingest microplastics reflecting their surrounding water contamination.
Characterization and enumeration of microplastic pollution in three fish species of the Upper Mississippi River
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Researchers found 891 microplastic particles across 281 fish from three species in the Upper Mississippi River, with fibers being the most common type and smaller fish containing proportionally more microplastics than larger ones. This confirms microplastic ingestion is widespread in freshwater fish — not just marine species — and the presence of styrene-isoprene, polyester, and ABS polymers highlights the diverse plastic sources contaminating major river systems.
Occurrence and amount of microplastic ingested by fishes in watersheds of the Gulf of Mexico
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Researchers quantified microplastic ingestion by fishes across several freshwater and estuarine watersheds of the Gulf of Mexico. The study documented widespread microplastic occurrence in fish from these environments, contributing important data about freshwater contamination at a time when most research had focused on marine ecosystems.
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