This Is AuburnElectronic Theses and Dissertations

Interactions of "Forever Chemicals" – Per and Polyfluoroalkyl Substances with Dissolved Organic Matter Extracted from Commonly Employed Soil Organic Amendments




Lawhon, John

Type of Degree

Master's Thesis


Crop Soils and Environmental Sciences


Per- and polyfluoroalkyl substances (PFAS) are a large group of chemicals that are highly persistent and ubiquitous in the environment. These compounds, known for their adverse effects on humans and the ecosystem, reach farmlands with irrigation water and land application of biosolids. The fate and bioavailability of PFAS in the soil environment are fundamentally influenced by their interactions with dissolved organic matter (DOM), the concentration of which in soil solutions is elevated due to land application of organic amendments. The development of efficient risk assessment and treatment strategies requires an understanding of the underlying mechanisms of PFAS interactions with DOM and its effect on contamination spread in the soil and water medium. This study examined the interactions of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) with DOM extracted from class B biosolids, animal manure, and plant derived composts, and a humic acid standard. The molecular structure of the DOM was analyzed using UV-vis absorbance, fluorescence excitation-emission matrices (EEM) coupled with Parallel Factor (PARAFAC) analysis, Fourier Transform Infrared (FTIR) spectroscopy, and size exclusion chromatography. The PFOS – DOM binding interactions were assessed using equilibrium dialysis and fluorescence quenching. Furthermore, to evaluate the impact of DOM on PFAS transport in soils, the adsorption and desorption of PFOS were measured using the B horizon of Gwinnett and Vaiden soil. Results demonstrate distinct molecular properties of DOM extracted from the different types of organic amendments. The biosolids have a large proteinaceous content, lower aromaticity, and moderate molecular weight. In contrast, plant-derived compost and humic acid are composed of a larger aromatic molecular structure and lessened proteinaceous content. DOM obtained from biosolid and manures exhibited the strongest interactions with PFOS (KDOC = 91, 724 L kg-1), while DOM of humic acid displayed the weakest (KDOC = 7,157 L kg-1). Binding of PFOS to DOM was correlated with the proteinaceous content (r = 0.71), carboxyl group content (r = 0.55), aromaticity (r = 0.70), and negatively correlated with degree of humification (r = -0.81). Fluorescence quenching results indicated direct interactions of PFOA and PFOS with humic and proteinaceous fluorophores, where up to a 50% decrease in fluorescence intensity of humic and proteinaceous fluorophores was noted. Moreover, following reaction with PFOS and PFOA, fluorescence intensity increased by up to 50% for fluorophores associated with humic and proteinaceous DOM extracted from biosolids, poultry litter, and humic acid. These results suggest that DOM undergo structural and compositional changes when interacting with PFAS. In the presence of DOM from biosolids, aged poultry litter, and public works compost, the adsorption of PFOS on Gwinnett soil increased by up to 120%, whereas DOM extracted from humic acid and peat moss decreased adsorption by 52%. Similar results were observed for the Vaiden soil. However, the highest increase in adsorption (122%) was observed in the presence of aged poultry litter DOM. Adsorption-desorption isotherms indicated pronounced hysteresis behavior, dependent on the presence and type of DOM in the adsorption reaction step, implying the importance of PFOS-DOM-soil ternary complexes. This study demonstrated a strong potential for using DOM molecular descriptors as predictors for the behavior of anionic PFAS in the soil and water environment. Importantly, the use of DOM descriptors and distribution coefficients have potential for further use in modeling efforts to predict the transport of PFAS in the environment. Further research should focus on establishing DOM molecular descriptors and binding coefficients between short and longer chain PFAS as well as zwitterionic and cationic moieties rather than just anionic.