Spatial distribution and mass transport of Perfluoroalkyl Substances (PFAS) in surface water: A statewide evaluation of PFAS occurrence and fate in Alabama
Graphical abstract
Introduction
Per- and polyfluoroalkyl substances (PFAS) are the focus of thousands of studies due to their adverse health effects in humans and wildlife. PFAS encompass a large group of anthropogenic organic substances widely used in industrial applications and consumer products, including in the coating of cookware and food packaging, stain- and water-repellent products and fabrics, as well as in the formulation of aqueous film forming foam (AFFF) fire extinguishers, ski wax, and much more (Johns and Stead, 2000; KEMI, 2015; Pan et al., 2018). In the late 1990s, 3M reported to the United States Environmental Protection Agency (US EPA) evidence that certain PFAS could bioaccumulate in humans (3M, 1998) and agreed to end the production of perfluorooctanesulfonic acid (PFOS) and its related salts by 2002 (3M, 2000). Since then, several studies have reported that certain PFAS might have negative health impacts in humans, including carcinogenic (Steenland and Winquist, 2021) and endocrine disrupting (Gong et al., 2019) effects, increased blood cholesterol levels (Seo et al., 2018), and obesity (Braun, 2017). In wildlife, PFAS can bioaccumulate and biomagnify through food chains (Xu et al., 2014), inhibit growth (McCarthy et al., 2017), and act as endocrine disruptors (Pedersen et al., 2016). Thus, the presence of PFAS in aquatic environments is of great concern.
Due to their stability and heterogeneity, the remediation of PFAS-contaminated waste is challenging (Ross et al., 2018), and PFAS are often discharged into the environment without proper treatment. Sources include municipal wastewater treatment plants (WWTPs), industrial facilities, landfills, airports, military bases, and firefighting training facilities, among others (Hu et al., 2016). As a result, PFAS have been identified on every continent, from remote Antarctica (Casal et al., 2017) to populous areas of Asia (Pan et al., 2017; Zushi et al., 2011) and Europe (Gobelius et al., 2018; Munoz et al., 2015). In the US, Alabama is a particular hotspot for PFAS. Previous studies, conducted in 2002 and 2017, identified an area of increased PFAS concentration in the Tennessee River downstream of several chemical facilities, including a 3M plant (Hansen et al., 2002; Newton et al., 2017). The 2017 study also identified nine previously unknown PFAS and two other novel substances that were structurally similar to existing PFAS (Newton et al., 2017). Even more troublesome, the Decatur WWTP distributed over 34,000 metric tons of biosolids contaminated with PFAS to local farmers between 1995 and 2008 (Lindstrom et al., 2011). Lindstrom et al. (2011) found PFAS levels up to 31,906 ng L−1 in surface water near fields that received the contaminated biosolids. In response, the Alabama Department of Environmental Management (ADEM) announced a consent order with 3M, stating that the company must remediate contaminated sites in the Decatur area, as well as “monitor, test, and research impacts of exposure” (ADEM, 2020). Similarly, high levels of PFAS were also identified in the Coosa River (Lasier et al., 2011) – the main drinking water source for several cities in Alabama. The City of Gadsden, AL is currently litigating against more than 30 textile companies located in Georgia, arguing that these companies are responsible for the high levels of PFAS in the Coosa River. Recently, ADEM conducted a survey in 290 public water systems (PWS) for 18 PFAS (ADEM, 2021). According to their report, PFAS were found in 57 PWS, with ∑PFAS reaching up to 384 ng L−1, indicating the presence of PFAS in their corresponding source waters, as these substances are not likely to be removed through conventional treatment processes (Crone et al., 2019).
While previous studies have greatly enhanced the understanding on PFAS sources and their overall distribution, much remains unknown regarding their transport and fate in the environment. This is partially related to the fact that most studies express PFAS contamination in terms of concentration, which is not sufficient to track contamination in large river systems. This is because aqueous concentrations are affected by a variety of environmental factors, such as precipitation and stormwater runoff. Thus, considering aqueous concentration alone can lead to erroneous conclusions regarding the amount and transport of contaminant mass through interconnected river systems. Moreover, identification of sources can be difficult, as variable environmental conditions may mask potential PFAS inputs. Mass flux analysis is a simple complimentary approach that combines volumetric discharge and aqueous concentration. Most studies have used the concept of mass flux to estimate yearly mass discharge of tributaries into lakes or bays, using an annual average flow rate. For instance, Ma et al. (2018) calculated the fluxes of tributaries discharging into Taihu Lake and used them to determine sources, while Zhao et al. (2020) calculated the mass discharge of tributaries into the Bohai Sea. Results from those studies enhanced the understanding of the fate of PFAS in the environment, but not so much about their transport behavior. On the other hand, Nakayama et al. (2010) performed a mass flux analysis to track the mass transport of PFAS in the Upper Mississippi River Basin, by calculating the mass flux for sampling points using a 72-h average volumetric flow rate.
The ultimate fate of PFAS in the environment remains unclear. Studies have shown that some PFAS can be removed from water by partitioning to sediments and suspended particulates, volatilization, and sequestration by biota and wildlife (Casal et al., 2017; Liu et al., 2019; Munoz et al., 2019), depending on their chemical properties. Regardless of the environmental compartment, most terminal (stable) PFAS will persist virtually unchanged (Guelfo and Adamson, 2018), hence their nickname “forever chemicals”. Thus, this study aims to determine the spatial distribution of seventeen PFAS in surface water in Alabama and identify trends in their transport behavior through a mass flux analysis. Results of the mass flux analysis were also used to identify locations within the state serving as potential PFAS source areas. This is the first study to use mass flux analysis to systematically track PFAS contamination in multiple river systems at a state level in the US and demonstrates that mass flux analysis is a broadly applicable, reasonably simple approach for capturing large-scale trends in the transport of PFAS through interconnected surface water systems.
Section snippets
Chemicals and reagents
Target analytes include six perfluorocarboxylic acids (PFBA, PFPeA, PFHxA, PFHpA, PFOA, and PFNA), six perfluorosulfonic acids (PFBS, PFPeS, PFHxS, PFHpS, PFOS, and PFNS), and five perfluoroethers (HFPO-DA, NaDONA, PF4OPeA, PF5OHxA, and 3,6-OPFHpA). For the above analytes, eleven are considered short-chain PFAS (PFBA, PFPeA, PFHxA, PFHpA, PFBS, PFPeS, and all the perfluoroethers). Analytical grade PFAS standards were purchased from Wellington Laboratories (Ontario, Canada). The molecular
PFAS profile in Alabama
Of the seventeen target analytes, only six were detected, including three short-chain and one long-chain perfluorocarboxylic acids (PFCAs): PFPeA, PFHxA, PFHpA, and PFOA, and one short-chain and one-long chain perfluorosulfonic acids (PFSAs), PFBS and PFOS. The perfluoroethers were not found in any of the samples. Despite the relatively low number of detected analytes, at least one PFAS was found in 88% (n = 65) of all surface water samples. The short-chain PFPeA was the most detected
Conclusions
The results of this study raise important considerations for the possible implications of PFAS to humans and wildlife in Alabama. PFAS were found to be ubiquitous in the majority of rivers and tributaries sampled, being detected in 88% of surface water samples, even in less industrialized areas, with ∑6PFAS levels reaching up to 237 ng L−1. PFAS can pose a risk to wildlife, especially in rivers where PFAS were found at higher concentrations. This could also indirectly affect humans that consume
Funding source
This work was supported by the Auburn University Presidential Awards for Interdisciplinary Research (PAIR) program to the Emerging Contaminants Research Team (ECRT) and the Auburn University Presidential Graduate Research Fellowship.
Funding sources had no involvement in the conduct of this research.
CRediT authorship contribution statement
Roger L. Viticoski: Conceptualization, Investigation, Methodology, Writing – original draft. Danyang Wang: Methodology, Formal analysis, Writing – review & editing. Meredith A. Feltman: Methodology, Formal analysis, Writing – review & editing. Vanisree Mulabagal: Formal analysis, Investigation, Supervision, Writing – review & editing. Stephanie R. Rogers: Methodology, Writing – review & editing. David M. Blersch: Methodology, Writing – review & editing. Joel S. Hayworth: Funding acquisition,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors would like to thank the graduate students Clayton Stone, Caren Custodio Mendonca, Laura Gomez Arias, Julia Bitencourt, and Andresa Bezerra for their support during sample collection.
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2023, ChemosphereCitation Excerpt :Consequently, the above potential hazards of PFOA/PFOS substitutes urge the exploitations of effective strategies to remove them from the environment. Indeed, non-destructive technologies, such as adsorption and membrane filtration, could achieve the removal (Du et al., 2015; Wang et al., 2018; Dixit et al., 2020), while they are unable to completely mineralize the PFOA/PFOS substitutes. Ultimately, it is necessary to apply the destructive methods for chemically degrading PFOA/PFOS substitutes, which, nonetheless, is highly challenging, fundamentally due to the extremely high C–F bond strength (531.5 kJ mol−1).