Spatial Distribution and Mass Transport of Per- and Polyfluoroalkyl Substances (PFAS) in Surface Water Systems

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a group of nearly 5,000 anthropogenic organic substances produced since the late 1940s. These substances have been used in various consumer products and industrial applications due to their unique chemical properties. The presence of PFAS in the natural environment is particularly concerning because of their recalcitrance and potential adverse health effects on humans and wildlife. Hundreds of studies have contributed to the growing understanding of PFAS, but there are still many unknowns regarding their behavior and fate once in the environment. Thus, this work aims to advance the understanding of the distribution, transport, and fate of PFAS in the environment, with a focus on surface water systems. This dissertation presents three novel research projects aiming to answer similar questions at different geographical scales. First, research data from 228 peer-reviewed journal articles were analyzed to assess the current state of knowledge regarding the global spatial distribution and specific profile of PFAS in the environment and provide guidance regarding environmentally relevant concentrations (ERCs). General information, including location, total and individual PFAS concentrations, author, year, and media, were extracted from these 228 studies. PFAS were detected in 43 countries across all continents between 1999-2021, with ΣPFAS reaching 2,270 μg/L in surface water, 7,090 μg/L in groundwater, and 2,450 ng/gdw in sediment. Worldwide information on PFAS concentrations was used to develop ERCs, recommended not to exceed 2,721 and 48,606 ng/L in studies evaluating PFAS in surface water and groundwater, respectively, and 137.9 ng/gdw in sediments to guarantee environmental relevance. ERCs are particularly important in designing controlled studies, in which parameters must mimic environmental conditions to ensure results are meaningful and representative. Furthermore, PFAS have been detected in several areas in the United States, especially in Alabama. Several cities in the state are struggling with PFAS contamination of their drinking water sources, but the overall distribution and sources of PFAS in the state are still mostly unknown. Moreover, tracking the transport of PFAS in the environment has been proven to be challenging, partially due to most studies expressing PFAS contamination solely in terms of aqueous concentration. Seventy-four surface water samples were collected in strategic locations across all major river systems in Alabama. Samples were filtered, processed in the laboratory through solid phase extraction (SPE), and analyzed using an ultra-high performance liquid chromatography, triple quadrupole mass spectrometer (UHPLC-MS/MS). At least one PFAS was detected in 88% of all samples, with ΣPFAS ranging from non-detect to 237 ng/L. PFAS distribution was not uniform across the state: while relatively high mean ΣPFAS were detected in the Coosa (191 ng/L) and Alabama (100 ng/L) rivers, these substances were not detected in the Conecuh, Escatawpa, and Yellow rivers. Trends in the transport characteristics of PFAS were investigated through a mass flux analysis by multiplying the aqueous concentration by the volumetric flow rate. Consistent increases in the mass fluxes of PFAS were generally observed as rivers flowed through the state, revealing the existence of numerous sources across the state. The highest mass flux (63.3 mg/s) was detected on the most downstream sampling point in the Alabama River, which eventually discharges into Mobile Bay. Results of this study confirm the ubiquity of PFAS in Alabama and demonstrate that mass flux is a simple and powerful complementary approach that can be used to broadly understand trends in the transport and fate of PFAS in large river systems. Several areas of interest emerged from this project, including a section of the Tallapoosa River Basin downstream from Thurlow Dam and the Chattooga River, part of the Coosa River Basin. This area was used as case study to further elucidate the sources and transport characteristics of PFAS through a mass flux analysis, in which eleven surface water samples were collected in August 2021. Four perfluoroalkyl carboxylic acids (PFCAs) were detected in all eleven samples from the Tallapoosa River Basin, with ΣPFAS ranging from 17.4 to 89.0 ng/L. Among the potential sources investigated, the Stone’s Throw Landfill seems to be a substantial source of PFAS in the Tallapoosa River Basin.