For several decades, aqueous film-forming foam (AFFF) formulations were widely used for training and operations involving fire suppression. These AFFF formulations contained relative high quantities of perfluorooctane sulfonate (PFOS), as well a range of other of per- and polyfluoroalkyl substances (PFAS). The objective of this project is to develop and refine a framework for assessing bioaccumulation and exposure risks of PFAS in threatened and endangered (T&E) species on AFFF-impacted site.

This project is being conducted in two phases. The objective of Phase I of this project was to develop a framework for conducting scientifically sound risk assessments for PFAS in T&E species at AFFF-impacted sites. The Phase I study involved (i) a comprehensive literature review of physical-chemical properties, bioaccumulation metrics and environmental concentrations; (ii) development of a risk assessment framework for assessing PFAS bioaccumulation and exposure risks in T&E species at AFFF-impacted sites; and (iii) application of the proposed framework to several DoD sites for which existing PFAS monitoring data were available. Ultimately, results will help guide future research efforts and risk assessment initiatives related to exposure of T&E species to legacy PFAS at AFFF-impacted DoD sites. Results are available in the Phase I Final Report.

To support the framework developed in Phase I, there is a need for reliable information regarding the partitioning properties of PFAS in biological media and tissues of biota. As such, the primary objective of the Phase II effort is to conduct laboratory-based investigations to determine the partitioning properties or “solubilities” of PFAS in biological media and organism tissues. The laboratory-generated data will then be used to parameterize mechanistic models representing PFAS bioaccumulation in aquatic and terrestrial food webs, including those comprising water-respiring and air-breathing T&E species. These models will be tested by comparing model predictions with observed data generated from a bioconcentration experiment using rainbow trout (Oncorhynchus mykiss), as well as other bioaccumulation data.

During the Phase I study, the approach generally followed conventional methods employed for ecological risk assessment, including exposure characterization, effects characterization, and risk estimation. In particular, the approach utilized a combination of field-based measurements and bioaccumulation modeling to evaluate exposure in T&E species. Toxicity Reference Values (TRVs) were derived using the available toxicity data and various methods.

In the Phase II effort, the research involves three tasks:

• Task 1 involves conducting a series of laboratory-based experiments for determining the partitioning properties and “solubilities” of PFAS commonly detected at AFFF-impacted sites in different matrices.
• Task 2 involves conducting a laboratory-based bioconcentration experiment with juvenile rainbow trout to ultimately determine the partitioning properties of PFAS in in-vivo tissues of aquatic organisms.
• Task 3 involves entering the measured partitioning properties into previously developed food web bioaccumulation and risk assessment models and then testing these models.

Based on the results of these tasks, the team will further evaluate the overall performance of the activity-based modelling and risk assessment approach for practical risk assessment purposes.

Phase I Results

Phase I efforts suggest that risk assessments based on PFOS may adequately represent the overall PFAS risk at a given site, especially if perfluoroalkyl acids (PFAAs) are the main PFAS class of concern.

Additionally, a preliminary mechanistic PFAS food web bioaccumulation model predicted internal PFAS exposure levels in biota at DoD sites reasonably well, with model predicted values generally within a factor of three of the observed field data. The developed PFAS food web bioaccumulation model indicates this mechanistic modeling approach may be useful for future risk assessments of T&E species potentially exposed to PFAS at AFFF-impacted DoD sites. 

Specifically, omnivorous and carnivorous birds, mammals and reptiles are shown to exhibit a relatively high degree of PFAS bioaccumulation and hence exposure risk, compared to aquatic organisms at a given site. Model predictions indicate that at some sites with elevated PFAS concentrations in sediments, concentrations in benthic invertebrates can attain levels similar to those expected to induce acute effects in aquatic organisms. Biomagnification of PFAS in aquatic insectivorous bird species (feeding on benthos) cause very high exposure levels and associated risks.

Finally, PFAS concentrations in soils were found to be very important for exposure risks in numerous T&E species within terrestrial food webs, including terrestrial reptiles. PFAS exposure risks to upper trophic terrestrial wildlife were in many cases high. Sites exhibiting high PFAS concentrations in soils are expected to cause high levels of risks to terrestrial organisms.

It is important to note that risk estimates for T&E species in the present Phase I study are based on scenarios that assume exposure occurs via concentrations at the studied DoD sites. The extent of interaction of T&E species and their prey with AFFF-impacted soils and surface waters is a major knowledge gap in the present assessment of PFAS exposure risks of these species at DoD sites.

The Phase I efforts demonstrated the potential and merit of a chemical activity-based approach for assessing bioaccumulation and exposure risks of PFAS to T&E species of concern. Laboratory-based measurements of various PFAS properties are still lacking. Accurate estimates of various properties will undoubtedly strengthen the reliability of the risk assessment approach used in Phase I and aid PFAS bioaccumulation modeling efforts.

The Phase II study will generate new data to improve our understanding of PFAS partitioning into different biological media and organism tissues to ultimately support risk assessment and improve bioaccumulation and risk assessment models for PFAS in T&E species. The study will provide testing results that will strengthen confidence in the application of the model’s results for practical bioaccumulation and exposure-based risk assessment of PFAS at AFFF-impacted DoD sites, and will also characterize uncertainty of the bioaccumulation and risk assessment of PFAS. In short, the generated data will help to strengthen predictive models used in ecological risk assessment of PFAS, with a specific focus on T&E species for which empirical approaches are often not an option. (Anticipated Phase II Completion - 2026)

Sun, J.M., B.C. Kelly, F.A.P.C. Gobas, and E. Sunderland. 2022. A Food Web Bioaccumulation Model for the Accumulation of Per- and Polyfluoroalkyl Substances (PFAS) in Fish: How Important Is Renal Elimination. Environmental Science Process Impacts, 24:1152-1164. doi.org/10.1039/D2EM00047D.