Presentation Title:
Assessing PFAS in Sediments: The Importance of Sediment-Water Dynamics in Chemical Fate and Transport, Risk Assessments, and Developing Regulations

Background/Objectives:

Per- and polyfluoroalkyl substances (PFAS) continue to draw increasing regulatory attention. Initially, the focus was on drinking water because it was recognized as the largest and most readily addressable human health exposure pathway. As PFAS research expands, more attention is being given to other pathways, including alternative human health exposure routes and ecological risk. This growing attention is sparking more regulations associated with other media. For example, the widespread presence of several PFAS in soils and sediments has been consistently confirmed at a number of United States Department of Defense (DoD) installations where aqueous film-forming foams (AFFFs) were used. The Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and Resource Conservation and Recovery Act (RCRA) listings of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) will continue to increase awareness of sampling for PFAS at contaminated sites, including those that may have impacted sediments. The focus on PFAS is leading to growing regulations that compel regulators to consider PFAS fate, transport, and possible toxicity when managing and remediating contaminated sediment sites. This includes understanding their risk to human health and the ecology and optimal remedial alternatives that will be effective at treating PFAS and minimizing risk.

The varied chemistries of PFAS also pose challenges to their remediation, especially for sediment matrices. Sediment remediation is typically expensive, technically challenging, and time-consuming. The current field-scale treatment of PFAS-impacted sediments is limited to stabilization/immobilization methods (e.g., carbon sorbents and others); however, long-term treatment efficiency still needs further investigation. A limited number of technologies are available for in situ treatment of PFAS from sediment. Several ex situ destruction technologies are being developed to remediate PFAS-impacted sediments. However, the ex situ nature poses additional challenges because it requires dredging and treatment.

The Environmental Protection Agency (EPA) has not yet developed guidance or screening levels to aid site managers in understanding whether PFAS sampling is needed at contaminated sediment sites. However, that has not prevented some states or even some EPA Regions from requesting sampling or implementing their own sampling, even when it is unclear how the results might be used. Managing PFAS-containing sediments (including understanding their risk), if the chemicals are detected at the site, continue to be approached on a site-by-site basis. As regulators try to provide guidance and establish metrics for sediment remediation and risk reduction, PFAS sediment dynamics in the aquatic environment is a relatively understudied field, with much more focus being attributed to soils, groundwater, and surface water transport. Aquatic sediments are an important interface in the story of comprehensive PFAS transport, as they can serve as both sinks and sources of PFAS to surface waters and aquatic organisms. When evaluating remediation efforts, it is important to discern if the sediment is a source or sink, and approaches for this determination should be further explored. Due to the variety in chemistry, chain length, and polarity, PFAS molecules can behave differently in the sediment-water environment. This dynamic is further influenced by several intrinsic factors such as total organic carbon (TOC), salinity, mineral content, pH, grain size, etc. Biota-sediment accumulation factor (BSAF) in benthic organisms and different hydrogeologic influences can play a combined role in the final fate and transport mechanism of PFAS.

The varied chemistries of PFAS also pose challenges to their remediation, especially for sediment matrices. Sediment remediation is typically expensive, technically challenging, and time-consuming. The current field-scale treatment of PFAS-impacted sediments is limited to stabilization/immobilization methods (e.g., carbon sorbents and others); however, long-term treatment efficiency still needs further investigation. A limited number of technologies are available for in situ treatment of PFAS from sediment. Several ex situ destruction technologies are being developed to remediate PFAS-impacted sediments. However, the ex situ nature poses additional challenges because it requires dredging and treatment.

Approach/Activities:

These uncertainties lead to needing more information on how others are approaching sediment management, risk assessments, and remediation when PFAS is detected at a contaminated sediment site. This session is meant to provide that information by assembling experts in the field that understand PFAS and issues unique to contaminated sediment sites, including PFAS fate and transport as it relates to sediment characterization, best practices for risk assessments, and appropriate remedial alternatives, given the wide range of chemical characteristics of these chemicals.

This panel will assemble a range of stakeholders to discuss the current state of knowledge regarding the sediment-water dynamics affecting the fate and transport of PFAS, remediation of PFAS, and the effect of PFAS on human health and ecology. Expanding beyond legacy PFAS, this panel will also highlight knowledge gaps and ongoing studies that focus on PFAS precursor fate and transport. This will include discussion from past research projects that include fate and transport of AFFF- and textile-derived sources of PFAS to the environment. It will also provide a comprehensive discussion of different remediation technologies for PFAS-impacted soils and sediments, their applicability, and limitations. With the increased demand for understanding the fate and transport of PFAS in the environment and their eventual remediation, this panel will highlight the importance of identifying PFAS sources and chemistry and how environmental practitioners might attain the environmental regulatory objectives.

Results/Lessons Learned:

This panel will result in an improved understanding of PFAS fate in light of sediment-water dynamics and how they apply to decision making and study design in the field of environmental assessment, risk assessments, and sediment remediation. Results from published studies will be discussed to highlight emerging knowledge gaps in the role of sediment-water dynamics, but also to identify future directions for research and method development. An overview of tools available for PFAS sediment studies will be provided, including discussion of passive samplers, sediment dispersion models, and ex situ treatment technologies. Each panel member will also discuss specific results from their ongoing or past work regarding PFAS in sediments and surface waters from academic, government, and consulting perspectives.

Heidi Bullock

Affiliation

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Assessing PFAS in Sediments: The Importance of Sediment-Water Dynamics in Chemical Fate and Transport, Risk Assessments, and Developing Regulations