AFFF formulations have been used by the DoD since the 1970s to suppress fires, and there are hundreds of sites with associated PFAS contamination. The DoD used AFFF mixtures containing significant quantities of perfluorooctane sulfonate (PFOS) and related perfluoroalkyl sulfonates such as PFHxS until 2002, when production stopped, although the DoD continued to use PFOS-containing AFFF stocks for some time after. Although the DoD’s legacy use of AFFF included various fluorotelomer-based formulations, the vast majority of DoD’s environmental liability likely results from the use of PFOS-based AFFF. Additional research on PFASs is timely given the USEPA’s recent drinking water health advisories for two common PFASs, perfluorooctanoic acid (PFOA) and PFOS, as well as the numerous states that are beginning to promulgate drinking water standards. SERDP has been funding research on AFFF contamination for several years to improve PFAS analysis, to develop tools for assessing the fate of PFASs in the subsurface, and to evaluate the potential for in situ remediation.
Ecological risk characterization for PFASs was recently identified as a clear and immediate information gap by the Tri-Services Environmental Risk Assessment Working Group (TSERAWG) and the EPA, as well as by the participants in the SERDP & ESTCP workshop. PFASs are persistent in aquatic and terrestrial environments, and are known to accumulate in fish and wildlife. Management of PFAS-contaminated sites requires ecological risk evaluations for listed and non-listed wildlife species. However, the basic PFAS ecotoxicological data necessary to derive soil or sediment-based clean-up levels (CULs) for AFFF sites are lacking. While single-compound CULs can be derived using standard soil or sediment toxicity tests, CULs for protecting higher trophic level organisms (e.g., threatened and endangered species) – or human health based on fish consumption – require a more complete understanding of fate and transport, as well as uptake, bioaccumulation, biomagnification, and trophic transfer kinetics.
Ecological risk assessments at AFFF sites are complicated by the fact that the PFASs occur in complex mixtures, with over 200 different fluorinated organic chemicals having been identified in AFFF-impacted waters and soils so far. Biota are exposed to a mixture of PFASs, but what remains a critical research need is the bioaccumulation, food-web biomagnification, and the relative potency of both individual PFASs and the mix of constituents present at AFFF sites. Determining these relationships for a range of PFASs in addition to PFOS and PFOA will allow more reliable risk assessments at AFFF sites.
Toxicity and kinetics of PFASs are, at least in part, driven by their physical and chemical properties. For instance, in mammals, shorter-carbon chain PFASs (such as PFHxA and PFBA) are less overtly toxic than longer-carbon chains (PFOS and PFOA). Differences in chain length also drive bioaccumulation rates since in general, as the rate of elimination decreases with increasing chain length. However, the uptake and elimination kinetics, absorption/binding efficiency, in vivo precursor transformation rates, and competitive bioaccumulation effects from PFAS mixtures remains relatively uncertain.
For aquatic environments, only PFOS has been found to significantly biomagnify up the food chain. The degree to which other compounds (e.g., PFHxS) bioaccumulate and biomagnify remains unknown. That PFASs are bioaccumulative in water is well-established, as all published Bioaccumulation Factors (BAFs) are > 1. However, to date the only BAFs in the scientific literature are for individual PFASs to soil/sediment invertebrates and to fish. Additional work establishing bioaccumulation (uptake) to organisms at the base of the food chain is needed for soil invertebrates, sediment infauna, and phytoplankton/zooplankton.
Workshop participants identified a number of research needs associated with bioavailability, bioaccumulation and biomagnification of PFASs. It is essential that proposers view the Workshop Report to obtain additional detail concerning these discussions.
