Studying the Breakdown of Fluorine-Free Firefighting Foams and Their Effects on the Environment

Background and Impact 

As firefighting foams gradually phaseout per- and polyfluoroalkyl substances (PFAS), fluorine-free foams (F3) are being adopted as alternatives. However, we don’t fully understand how these fluorine-free foams affect the environment. F3 use high concentrations of hydrocarbon surfactants to create foam but these surfactants can be more toxic to mammals and aquatic life than the PFAS-containing foams they are replacing (Ateia et. al 2023). Therefore, it is important to study the toxicity, impact, and environmental fate (where they go and what they do along the way) of F3 to ensure they are safe PFAS alternatives.  Additionally, assessing the impact of F3 on freshwater aquatic systems provides valuable background information for the emergency response community and for other stakeholders who monitor these ecosystems as part of a regulatory framework. 

Biodegradation 

Understanding biodegradation is important because it determines how firefighting foams break down in the environment, affecting their long-term impact on ecosystems. Bench-scale aerobic and anaerobic biodegradation tests have been conducted to determine if F3 can break down naturally. These tests were performed using modified Organization for Economic Cooperation and Development (OECD) methods on two recently approved Milspec foams, designed for land-based military firefighting operations. Results showed high degradation rates of F3 in aerobic environments, but slower and incomplete degradation in anaerobic environments. Both degradation tests indicated the production of intermediate byproducts. This study highlighted the need for a greater understanding of the fate and transformation of F3 in the environment. Microbial community diversity was also shown to decrease upon exposure to F3 in the biodegradation tests. Loss of microbial diversity shows F3 are likely harmful to microbial communities and warrant further exploration. 

Aquatic Toxicity 

In a preliminary study, EPA conducted an assessment of the short-term chronic toxicity of two Milspec F3 foams (Foams A and B) using 4-day Daphnia magna short-term chronic tests, 7-day Ceriodaphnia dubia chronic reproduction tests, and 7-day Pimephales promelas short-term growth tests. Toxicity tests of Foam A resulted in C. dubia being 2-fold more sensitive than D. magna, with P. promelas being least sensitive, indicated by no detectable effect on growth at concentrations tested. Toxicity tests of Foam B resulted in C. dubia being 15-fold more sensitive than D. magna. P. promelas was least sensitive, as no effects on growth were detected at the concentrations tested. Diethylene glycol butyl ether (DGBE) and sodium lauryl sulfate (SLS), two surfactants used at high concentrations in both foams, were quantified in initial samples to assess surfactant presence in initial spiked samples. Foam A contained surfactant concentrations closer to expected at 119% for DGBE and 111% for SLS.  

In addition, EPA conducted a 24-hour acute test to evaluate toxicity and sublethal effects on behavior and gene expression in larval P. promelas to two additional Milspec F3 (Foams C and D) and one PFAS-containing foam. Toxicity was similar for F3 foams but was orders of magnitude higher than the PFAS containing foam. In contrast, the PFAS foam altered behavior in most of the tested concentrations, whereas behavioral effects were only observed at the highest concentrations for the PFAS-free formulations. All three affected cellular functions associated with cell stress and xenobiotic metabolism and neurogenesis, transcription/translation. Together, these results suggest that though PFAS-free formulations are significantly more acutely toxic, however, all three formulations impact a broad array of cellular functions during a relatively short period of exposure, suggesting their potential to negatively impact aquatic ecosystems.    

Terrestrial Toxicity 

In a series of acute, chronic, and behavioral (avoidance) tests, the F3 showed widely different acute toxicity to earthworms. One F3 formulation was more acutely toxic than a common PFAS-containing product. Earthworms strongly avoided soils treated with both F3 and PFAS-containing foams (Yeardley et al. 2024).  

Ongoing Research  

EPA’s Experimental Stream Facility (ESF) in Cincinnati, OH, is a one-of-a-kind facility for conducting ecotoxicological and ecosystem structure/function effects studies using stream mesocosms. Small stream ecosystems play a critical role in maintaining the quality of larger receiving waters including drinking water sources. It is important to understand how they respond to and react with stressors and pollutants moving from landscapes, through them, and to larger multi-use receiving waterbodies. The ESF contains 16 artificial streams (mesocosms) in a highly engineered set-up for testing the effects of current and emerging contaminants like F3 on aquatic life. The ESF also has the capability of conducting single species testing in situ as well as ex situ (in series).  In parallel with mesocosm tests, EPA conducts standard single species Whole Effluent Toxicity (WET) tests in EPA-Cincinnati's Aquatic Research Laboratory. With the parallel testing, results can be connected to regulatory programs like Ambient Water Quality Criteria for the protection of aquatic life. 

This project aims to demonstrate the potential ecological effects of F3 in temperate freshwater streams by dosing three different F3 formulations (Foams E, F, and G) into the stream mesocosms at ESF. The tests will allow for a whole ecosystem approach to: 

The stream mesocosm research is critical given that so little is known about the fate, transport, and toxicity of the chemicals associated with F3 in the aquatic environment. This study will provide necessary information to develop indicators of environmental health related to F3 and to more broadly increase our theoretical and applied understanding of the impact of F3 in freshwater environments. This project is of value to regional and cross-agency partners given it provides information to the emergency response community regarding the potential impact of response activities related to freshwater ecosystems and provides valuable background information for other stakeholders who monitor these ecosystems. 

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