Per- and polyfluoroalkyl substances (PFAS) are among the most widespread and persistent environmental pollutants. There are more than 3,000 PFAS chemicals in use for industrial and consumer applications, including firefighting foams, non-stick cookware, food packaging and water- and stain-resistant fabrics.
In recent years, PFAS has come under wider scrutiny due to its persistence in the environment and potential risks to human health and the environment. An analysis of EPA monitoring data reported elevated levels of PFAS in groundwater and surface water used for public water supplies associated with industrial plants producing or using PFAS, military bases and airports used for firefighting exercises, and publicly owned treatment works (POTWs).
Contaminated sites often contain multiple kinds of PFAS chemicals. However, available ecotoxicity data are limited to just a few PFAS chemicals. Without accurate toxicity data for the remaining PFAS chemicals, researchers cannot perform a robust risk assessment or make effective recommendations for remediation and risk reduction. An alternative approach was needed to evaluate PFAS ecotoxicity with available data and to target areas where future research is needed.
Battelle developed a tiered “weight of evidence” (WOE) approach to extrapolate toxicity for PFAS contaminants without toxicity data. This approach leveraged available knowledge from the PFAS compounds that have been studied for application to chemicals lacking toxicity data.
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It has been known for some time that PFAS with longer chains of fluorinated carbons are more persistent in the environment and exhibit greater ecotoxic effects than PFAS with shorter chains. Leveraging data on known relationships between chain length and functional group and environmental impacts, Battelle evaluated available toxicity data for PFAS chemicals with different chain lengths and different types of functional groups (e.g., sulfonic vs. carboxylic). The literature review included an examination of the effects of exposure of different types and concentrations of PFAS on aquatic invertebrate organisms such as Daphnia, a small planktonic crustacean at the base of many aquatic food chains.
The tiered WOE extrapolation framework has demonstrated utility for ecological toxicity assessment of PFAS chemicals. It provides a systematic and transparent approach to identify surrogates for PFAS compounds that lack toxicity data. This approach could facilitate risk assessment for sites contaminated with PFAS compounds that have not been studied directly.
Researchers have also identified key information gaps. For example, there are more toxicity data available for PFAS with carboxyl functional groups than for sulfonates. Targeted toxicity research for a few representative sulfonate compounds would allow for more robust extrapolation to other sulfonates.
Additional work remains to be done to further refine the model, including targeted toxicity research and analysis to fill gaps in our understanding of basic chemical properties for some PFAS compounds. Toxicity testing using well-characterized environmental mixtures of PFAS compounds from defined sources would also provide additional data to refine and evaluate the surrogate approach. As more research is done and the model continues to evolve, the tiered WOE approach could be a valuable tool for risk assessment and remediation decisions for sites contaminated with lesser known PFAS compounds as well as sites with a mixture of PFAS.