Feasibility of Biodegradation of Polyfluoroalkyl and Perfluoroalkyl Substances
- Author(s): Tseng, Nancy Shiao-lynn
- Advisor(s): Mahendra, Shaily
- et al.
Polyfluoroalkyl and perfluoroalkyl substances (PFASs) are highly stable organic compounds, which contain multiple carbon-fluorine bonds. They are used in various commercial products, including aqueous fire-fighting foams (AFFF) and products with non-stick coatings. However, these compounds are reproductive and developmental toxicants, endocrine disrupters, and potential human carcinogens. They are found globally as emerging contaminants in groundwater and surface water resources. The two most persistent and widely detected PFASs are perfluorooctanoate (PFOA) and perfluorooctane sulfonic acid (PFOS). Other fluorinated compounds, such as fluorotelomer alcohols (FTOHs), can transform to PFOA and PFOS in the environment via biological and physico-chemical processes. Current methods to remove PFASs from waste streams and contaminated environments (e.g. activated carbon adsorption, sonolysis, photodegradation, and reverse osmosis) are expensive, impractical for in situ removal, use high pressures and temperatures, or result in toxic waste. In contrast, biodegradation may lead to a cost-effective, in-situ remediation strategy for PFASs. Bioremediation has been successfully used for other recalcitrant contaminants, including chlorinated volatile organic compounds.
This thesis investigated the biodegradation potential of PFASs. The two groups of laboratory strains tested in this study were ligninolytic fungi (Phanerochaete chrysosporium and Aspergillus niger) and oxygenase-expressing bacteria (Pseudonocardia dioxanivorans CB1190, Methylosinus trichosporium OB3b, Burkholderia cepacia G4, and Pseudomonas putida F1). All strains are known to degrade xenobiotic compounds. In addition, 5 fungal strains and 2 strains of aerobic bacteria isolated from an aqueous fire-fighting foam (AFFF)-contaminated site were also evaluated for their PFAS biodegradation potential. Results indicate that P. chrysosporium was able to transform about 50% 6:2 FTOH and 70% 8:2 FTOH in 28 days. Major metabolites of 6:2 FTOH included 5:3 polyfluorinated acid (40%), 5:2 sFTOH (10%), PFHxA (4%), and others (about 1% each). Fewer metabolites were produced after 8:2 FTOH degradation, such as 7:2 sFTOH (6%), PFOA (5%), 7:2 Ft ketone (3%), and others (< 1% each). In contrast to P. chrysosporium, A. niger did not transform 6:2 FTOH during 35 days. Among the environmental fungal isolates, Envi 5 and Envi 7 transformed about 20% PFOS within 28 or 14 days, respectively, and only Envi 7 could partially transform about 20% PFOA within 14 days. There was a small increase in fluoride ions, but no metabolites were measured. None of the tested bacteria were able to transform PFOA within 7 days. This study demonstrated that fungi would be likely candidates for bioremediation of PFASs. Consequently, ongoing research is investigating the metabolites, enzymatic reaction kinetics, and conditions favorable for in-situ bioremediation.