The widespread use of aqueous film forming foams (AFFF) containing PFAS at airports all over the world has resulted in contamination of ground and surface water, and soil. In addition to the many ecosystem effects that are still being studied, how are microbial communities affected? Which PFAS are microbes able to degrade and how does this affect PFAS concentrations and compound distribution?

Scientists from the University of New South Wales, Western Sydney University and the Environmental Sciences Group (ESG) out of Canada’s Royal Military college set out to answer these questions in a study recently published in The Science of the Total Environment¹. SGS AXYS used an earlier version of our isotope dilution PFAS method to measure to measure a suite of PFAS including perfluorinated carboxylates C4-C12 including PFOA, perfluorinated sulfonates PFBS, PFHxS and PFOS, and multiple precursors including 4:2 FTS, 6:2 FTS, 8:2 FTS, 6:2 FTCA, 8:2 FTCA, 10:2 FTCA, 6:2 FTUCA, 8:2 FTUCA, 10:2 FTUCA, FOSAA, MeFOSAA, and EtFOSAA.

While perfluorinated carboxylates and sulfonates cannot be metabolized in the environment (hence the forever chemicals description), PFAS are subject to transformation and this study was able to assess these transformations in detail thanks to the extensive precursor data provided by SGS AXYS, and the use of the TOP assay (not SGS AXYS data) by the researchers.The study then used DNA extraction and PCR-amplification techniques to assess the relative abundance of bacteria by community.

PFAS occurrence data showed that the site had concentrations well in excess of regulatory limits with “aqueous PFAS concentrations of up to 620,000 ng/L and 3,500,000 ng/Lin the source area of the deep and shallow aquifers, respectively”. PFHxS was the most significant PFAS detected, which is indicative of the type of AFFF that was historically used at the site. While PFHxS is a shorter chain length than PFOS and less widely studied on toxicological effects, there is evidence of high half lives in humans², even higher than PFOS and PFOA. PFOS was the next-highest PFAS detected. TOP assay results indicated mostly precursors of carbon chain length 6 or lower presence. Like in previous studies, the precursors were higher in the source zone showing that they were either being transformed in the environment.

Based on the bacterial composition data, authors concluded that macro-effects such as oxidation/reduction potential and pH of the water influenced the microbial community to a much larger extent than PFAS, which is not surprising. But interestingly, in certain localized areas,

the statistical analysis suggests that PFHxA, PFHpA and PFBS were significant (p > .05) drivers of overall community composition indicating that on localized scales within this dataset individual contaminants may be more influential to determine overall drivers of composition

The correlation data identified several bacterial communities that correlated either positively or negatively with individual PFAS. One type of bacteria, Oxalobacteraceae were relatively more abundant in areas with higher PFAS concentrations. This family are generally more tolerant to environmental stress. The study showed some very interesting dose-response type effects as well.

As the authors conclude:

Positive correlations (between PFAS concentrations and microbe family abundance) may ultimately provide important insights related to development of biodegradation technologies for PFAS impacted sites, while negative correlations further improve our understanding of the potential negative effects of PFAS on ecosystem health.

Multi-disciplinary research that links high-quality PFAS occurrence data with microbial abundance data in the field is rare, and as this study showed, can produce some interesting insights!

References

1. O’Carroll, D.M., Jeffries, T.C., Lee, M.J., Le, S.T., Yeung, A., Wallace, S., Battye, N., Patch, D.J., Manefield, M.J., Weber, K.P., 2020. Developing a roadmap to determine per- and polyfluoroalkyl substances-microbial population interactions. Science of The Total Environment 712, 135994. https://doi.org/10.1016/j.scitotenv.2019.135994
2. Li, Y., Fletcher, T., Mucs, D., Scott, K., Lindh, C.H., Tallving, P., Jakobsson, K., 2018. Half-lives of PFOS, PFHxS and PFOA after end of exposure to contaminated drinking water. Occup Environ Med 75, 46–51. https://doi.org/10.1136/oemed-2017-104651