Biotic and Spatial Factors Driving Microplastic Abundance in the Gizzard of Green-winged Teal (Anas c. carolinensis) in Historic Antebellum Rice Fields in South Carolina 

Derived from the polymerization of monomers, plastics are synthetic organic polymers whose large-scale production began in 1950. Improper plastic waste management has become a rising problem facing humanity as oceans, waterways, and terrestrial areas all become choked with plastic waste products. Microplastics are introduced into the environment via several anthropogenic activities, such as cloth washing, use of hygiene care products like exfoliants, and industrial by-products (Velis et al., 2017) (Figure 1). Consequently, there has been an increasing concern about microplastics as an emerging pollutant. Microplastics are plastic particles ranging from 1 µm – 5 mm in size, though the absolute lower size limits vary. These microplastics originate as primary or secondary plastics. Primary microplastics are manufactured and include products like exfoliating beads in cosmetic cleansers, plastic microspheres used in biomedical and life sciences research, and industrial abrasives. Secondary microplastics result from the deterioration and fragmentation of larger microplastic pieces into smaller fragments.  

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Microplastics are a significant threat to both wildlife and humans. The ingestion of microplastics by organisms can result in physiological and behavioral impairments. Additionally, microplastics can absorb and transport toxic compounds (i.e., PFAS), serving as a vector for these substances within food webs. Coastal ecosystems are particularly vulnerable to microplastics as they receive high input from urban runoff, wastewater discharge, and industrial effluents. Microplastic accumulation in coastal environments can threaten the biodiversity and function of these systems, which are crucial for migratory species and local communities.  

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Historic antebellum rice fields (HARF) in Coastal South Carolina (SC) with origins in the transatlantic slave trade in the 1600s are a crucial habitat for waterfowl. Nowadays, ~33,000 acres of tidal HARFs remain functional and provide habitat for a myriad of waterfowl species. According to Masto et al. (2023) and Hanks et al. (2021), these rice fields are highly utilized by wintering dabbling ducks. Approximately 30% of all dabbling ducks in the Atlantic Flyway winter in the South Atlantic region, particularly in coastal SC. Thus, tidal functional HARFs in SC are a crucial habitat for wintering dabbling ducks in the Atlantic Flyway. 

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Currently these critical wetlands are under threat from microplastics. Adjacent anthropogenic development has the potential to deposit microplastics in these unique systems, threatening the survival of waterfowl that depend on HARFs. Given these threats, I aim to investigate the presence and concentration of microplastics in the gizzard of Green-winged Teal (GWTE) as a bioindicator for microplastic contamination in SC’s HARFs. 

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The goal of this research is comprised of three objectives: 1) Assess the presence and concentration of microplastics in the gizzard of GWTE in SC’s HARFs. GWTE was the most harvested species (n=641) in the SC Department of Natural Resources Waterfowl Management Areas in the 2024-25 hunting season. Consequently, it is an optimal surrogate species, since hunters may be the terminal link in the microplastic trophic pathway. Microplastic presence and concentration will be assessed utilizing chemical digestion with potassium hydroxide (KOH) and hydrogen peroxide (H2O2) paired with the Agilent 8700 Laser Direct Infrared (LDIR) chemical imaging device (Figure 2). 2) Utilize a linear mixed effects model to determine whether microplastic concentration, microplastic type, and polymer type is affected by mass, sex, predominant species, location, watershed, urbanization, and population density. 3) Compare the performance of the Agilent 8700 LDIR to a light microscope for identifying microplastic types and measuring microplastic concentration. 

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At this point in time, I am chemically digesting the gizzard contents and will begin chemical imaging shortly. Nonetheless, given the findings of Gray et al. (2018) and the tidal nature of coastal HARFs, I predict microplastics will be present in the gizzard of GWTEs. Additionally, I predict synthetic particle polymer types to be congruent with the findings of Boucher et al. (Unpublished), where rubber and polyamide are highly abundant. Furthermore, I predict sex, predominant prey species, urbanization, and population density will significantly influence microplastic abundance. Finally, I predict the light microscope will identify trends in the abundance of microplastics, but it will underestimate overall abundance. 

This research effort would not have been possible without the support of the SC Department of Natural Resources, Southeast Mitigation, Mississippi State University, Nemours Wildlife Foundation, The Wildlife Society – Wetlands Working Group, and the Whitmire Laboratory. 

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Citations 

Boucher, M. N. Unpublished data. Regional Alligator Diet and Ecotoxicology of Contaminant of Emerging Concern in American Alligator (Alligator mississippiensis). Clemson University, SC 

Gray, A. D., Wertz, H., Leads, R. R., & Weinstein, J. E. 2018. Microplastic in two South Carolina Estuaries: Occurrence, distribution, and composition. Marine Pollution Bulletin, 128, 223-233. 

Hanks, R. D., Baldwin, R. F., Folk, T. H., Wiggers, E. P., Coen, R. H., Gouin, M. L., ... & Fields-Black, E. L. 2021. Mapping antebellum rice fields as a basis for understanding human and ecological consequences of the era of slavery. Land, 10(8), 831. 

Masto, N. M., Hsiung, A. C., Kaminski, R. M., Ross, B. E., Kneece, M. R., Wilkerson, G. L., ... & Anderson, J. T. 2023. Waterbird–habitat relationships in South Carolina: implications for protection, restoration, and management of coastal and inland wetlands. Restoration Ecology, 31(7), e13956. 

Velis, C., Lerpiniere, D., & Tsakona, M. 2017. Prevent Marine Plastic Litter - Now! An ISWA facilitated partnership to prevent marine litter, with a global call to action for investing in sustainable waste and resources management worldwide. Report prepared on behalf of the International Solid Waste Association (ISWA). An output of ISWA Marine Litter Task Force. ISWA September 2017. Vienna, pp.75.