Date of Award
8-2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Environmental Toxicology
Committee Chair/Advisor
Kylie Rock
Committee Member
Barbara Campbell
Committee Member
Peter van den Hurk
Committee Member
Scott D. Hamilton-Brehm
Abstract
Per- and polyfluoroalkyl substances (PFAS) are a diverse class of synthetic chemicals that have become globally distributed due to their extensive use in industrial and consumer products and their extraordinary resistance to environmental degradation. Their persistence and documented toxicity have made them a growing concern in coastal environments, particularly in estuaries where urban runoff, wastewater, and industrial discharges concentrate these compounds. Estuaries are unique in that tidal mixing and interactions with fine-grained sediments and organic matter promote PFAS retention, while the microbial communities living directly within estuarine sediments are positioned where PFAS preferentially accumulate, creating conditions for prolonged exposure and potential biological interaction. Despite this, relationships between PFAS contamination, sediment characteristics, and microbial community structure remain poorly understood, especially across systems with different levels of urbanization. This study examined these relationships in two South Carolina estuaries with different levels of urbanization, Charleston Harbor and St. Helena Sound, across multiple sampling periods throughout the year. PFAS concentrations were measured in water and sediment, sediment grain size and organic matter were characterized, and microbial community composition was assessed using 16S rRNA gene sequencing. Preliminary cultures were also initiated to explore whether Charleston Harbor sediment microbial communities were capable of breaking down PFOS. Water column PFAS concentrations were consistently higher in Charleston Harbor across multiple compound classes and sampling periods, which reflect direct inputs from a heavily v urbanized watershed. Sediment PFAS concentrations were more variable, with a pronounced spike at one Charleston Harbor site in October 2024 that disappeared by January 2025, suggesting that sediment in this system is not acting as a stable long-term sink. Sediment composition differed significantly between estuaries, with Charleston Harbor showing higher silt, clay, and organic matter content and St. Helena Sound higher sand content, and clay content was positively correlated with organic matter in both systems. Microbial communities were dominated by Gammaproteobacteria across all sites and timepoints. Beta diversity differed significantly between estuaries in October and May but not in January or March, while alpha diversity showed no significant differences in any sampling period, suggesting that environmental differences between estuaries, including PFAS contamination, may have influences community composition without substantially reducing species richness. PFAS and microbe associations shifted substantially between October and January, coinciding with a decrease in PFAS concentrations, and sediment properties were only significantly associated with microbial composition in October. Preliminary culturing showed significant higher bacterial cell counts in PFOS-treated cultures after 30 days, and early NMR results provided evidence of possible transformation products, though these findings require further experiments to confirm. These results highlight the dynamic nature of PFAS distribution and microbial responses in estuarine systems and suggest that sediment microbial communities from chronically contaminated estuaries may harbor taxa capable of PFOS transformation, which warrants further investigation.
Recommended Citation
Padgett, Zachary J., "Evaluating PFAS and Marine Microbial Interactions in Estuarine Sediments With Varying Urbanization and Assessments of Microbial Responses to PFOS" (2026). All Theses. 4833.
https://open.clemson.edu/all_theses/4833