Polyfluoroalkyl Substances

Per- and Polyfluoroalkyl Substances

Per- and polyfluoroalkyl substances (PFAS), called “forever chemicals,” have strong carbon−fluorine bonds that under typical environmental conditions are not broken down. Due to their unique properties and ubiquity, the monitoring and remediation of PFAS has required new approaches and adaptations to nearly every aspect of cleanup from sampling and analytical methods to treatment practices. While bioremediation is frequently an attractive cleanup option at contaminated sites because of its relatively low cost and low energy requirements, it is another area where additional research and innovation are needed to develop an effective solution for PFAS.

Biodegradation Challenges

There are several aspects of PFAS that make their biodegradation to non-toxic end products a challenge:

• Fluorinated compounds are rare in nature and are usually monofluorinated rather than perfluorinated, so most microorganisms have only been exposed to compounds with this degree fluorination in the past century.
• The carbon-fluorine bond is very strong, and only a limited number of defluorinating enzymes have been identified to date.
• The redox potential of reductive deflourination is on the border of what is energetically favorable for microorganisms.
• Over 16,000 PFAS compounds have been produced, and their varying properties and susceptibility to biodegradation add another layer of complexity.
• PFAS and fluoride are toxic to microorganisms and can have negative effects at both the cellular and community levels.
• Concentrations of 4 ppt are required to meet the EPA’s maximum contaminant levels for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). These low concentrations in the environment may not be sufficient to support microbial growth.

Promising Advances in PFAS Research

Recent studies have demonstrated that multiple microorganisms have the potential to biotransform polyfluorinated compounds, and at least one microorganism, Acidimicrobium A6, may be able to biodefluorinate PFOA and PFOS. Due to the low concentrations of PFAS typically found in the environment, co-metabolic pathways may play an important role in the field. Oxygenase and dehalogenase enzymes have been identified as potentially responsible for co-metabolic PFAS biotransformation.

PFAS biodegradation by fungi is also of interest since they have a broader range of oxidative enzymes compared to microorganisms. For example, Gloeophyllum trabeum, Trametes versicolor, and Phanerochaete chrysosporium have been reported to biotransform 6:2 fluorotelomer alcohol (6:2 FTOH). P. chrysosporium was the subject of recent research examining protein-level responses to PFAS where proteomics was used to identify potential resilience pathways that are activated under PFAS stress.

Despite the challenges associated with PFAS degradation, microorganisms, enzymes, and fungi of interest have been and continue to be identified. Further investigation is needed to gain a better understanding of the reaction mechanisms involved and to determine if the complete detoxification of parent compounds is possible. Closing these data gaps will help determine how biodegradation processes can be leveraged to develop effective PFAS bioremediation strategies.

At Microbial Insights we require the highest levels of validation before we add a new microbiological assay for bioremediation purposes. We are monitoring the literature on PFAS degradation closely and are excited about the current research and future possibilities.