Bioaccumulation, Fate, and Treatment of Per- and Polyfluoroalkyl Substances (PFAS)
Authors:   , Lewis Asa James , Sales Christopher 
Published: February 2023

Per- and polyfluoroalkyl substances (PFAS) are a large and diverse class of man-made chemicals that are persistent and difficult to degrade in the environment. PFAS are characterized by the presence of carbon-fluorine bonds, the strongest bond in organic chemistry, which leads to great thermal and chemical stability. Often these properties provide industrial and consumer products with chemical and temperature resistance, surfactant behavior, and stain or water resistance. Currently, the problem of PFAS in the environment starts with their synthetic generation, use in products, and subsequent release to the environment where they can bioaccumulate and persist. PFAS have globally impacted aquatic ecosystems through major pathways such as direct release into the environment (e.g., fire-fighting trainings with aqueous film forming foams (AFFF)), inadequately treated industrial effluents, land-applied biosolids, and atmospheric deposition. Once released to the environment, specifically in water, many PFAS compounds tend to accumulate in ecosystems through bioaccumulation. In water, some PFAS are mobile, pose risks to all levels of an ecosystem, and are particularly difficult to remove or degrade. To address the release and accumulation in the environment, major strides must be made in terms of regulations, development of analytical techniques, mechanistic pathways understanding related to fate and transport, and advancement of treatment technologies to address the pollution whether it is large scale or site-specific remediation efforts. The goal of this dissertation is to provide further insight into bioaccumulation of PFAS in aquatic matrices, fate and transport in land-applied biosolids, and to develop a plasma treatment technology to destroy PFAS. Regarding bioaccumulation in aquatic matrices, geochemical factors have been demonstrated to impact PFAS partitioning in aquatic ecosystems and to impact bioaccumulation, but little is known related to the mechanistic understanding of the effects of elevated divalent cation concentrations of magnesium (Mg²⁺) and calcium (Ca²⁺) on macroinvertebrates. Therefore, as part of this dissertation, the impacts of Mg²⁺ and Ca²⁺ on PFAS bioaccumulation in three different macroinvertebrates species, Lumbriculus variegatus (L. variegatus), Elliptio complanata (E. complanata), and Physella acuta (P. acuta) were investigated, where it was demonstrated that the increased divalent cations concentrations impact the bioavailability of PFAS and the mechanisms responsible were discussed. L. variegatus had significantly higher PFAS bioaccumulation than P. acuta and E. complanata, likely due to higher levels of activity and interactions/ingestion of the contaminated sediment. "High Mg²⁺" (7.5 mM Mg²⁺) and "High Ca²⁺" (7.5 mM Ca²⁺) conditions generally had observable higher bioaccumulation factors (BAFs) than the "Reference Condition" (0.2 mM Ca²⁺ and 0.2 mM Mg²⁺) for PFAS with perfluorinated chain lengths greater than six carbons. Long-chain PFAS dominated the PFAS profiles of the macroinvertebrates for all classes of compounds studied, PFCA, PFSA, and FTS. These results indicate that the specific organism studied is most impactful regarding bioaccumulation, but divalent cation concentration has observable impacts between species depending on the environmental conditions. With respect to the release of PFAS from land-applied biosolids, the influence of microbial weathering on the partitioning of PFAS over a period of three months was investigated to see the impacts on fate and transport in biosolids. We found that the PFAS biosolids-water partitioning coefficients (Kd) were demonstrated to decrease, on average, 0.4 log over the course of the study. Additionally, the solid characteristics were characterized (lipids, proteins, and organic matter) and were observed to have sharp decreases over the first ten days, aligning with the most rapid changes in Kd. As a result, a multiple linear regression model was built to predict PFAS partitioning behavior in biosolids based on the biosolids characteristics and PFAS characteristics. Among the evaluated independent variables, statistical analyses demonstrated that the most significant solids characteristics that impacted PFAS partitioning were organic matter, proteins, lipids, and molecular weight of organics. A multiple linear regression model was built to predict PFAS partitioning behavior in biosolids based on solid characteristics of the biosolids and PFAS characteristics with a R2 value of 0.7391 when plotting predicted and measured log Kd. The findings from this work reveal that microbial weathering can play a significant role in the eventual fate and transport of PFAS and their precursors from biosolids. Since PFAS have been demonstrated herein to accumulate in aquatic matrices and rapidly partition from biosolids during biotic weathering processes, there is a need to effectively remove PFAS from water to decrease the environmental accumulation and transport. We report as part of this dissertation the development of a non-thermal plasma treatment system to degrade PFAS in liquid solutions. It was observed that this technology was able to rapidly degrade PFAS compounds but the degree of degradation and defluorination was highly depending on perfluorinated alkyl chain lengths, with those compounds with greater than 8 perfluorinated carbons achieving greater than 90% removal in one hour of treatment. The combination of the energy efficiency of this treatment being on the order of magnitude of other emerging destructive technologies and its effectiveness shows promise for the application of non-thermal plasmas for PFAS removal in water. The lowest EEo for PFOS was 23.2 kWh/m3/order and 213.4 kWh/m3/order for PFOA, similar with existing technologies (which range from 10 to 10,000 kWh/m3/order). These results indicate that non-thermal air plasma discharges are promising technologies for treatment of PFAS that should be further researched and developed.