Biodegradation Potential of Perfluorooctanoate and Perfluorooctane Sulfonate

Perfluorooctanoate (PFOA) and Perfluorooctane sulfonate (PFOS) are two environmentally persistent perfluorinated compounds widely used for many industrial and consumer products due to their high thermal, oxidative resistance and surface repellence to water and oil. Their reproductive and developmental toxicity in lab animals and their persistence in environment have raised a serious concern for humans and animals. Trace amounts of these compounds have been found in water bodies, human blood, and wildlife samples. PFOA and PFOS are currently listed in Environmental Protection Agency's drinking water Contaminant Candidate List and in the list of Persistent Organic Pollutants in the Stockholm Convention.

The strong covalent bond between carbon and fluorine present in PFOA and PFOS makes them stable and resistant to conventional treatment processes. Several advanced chemical processes can degrade PFOA and PFOS under high temperatures and pressures or other extreme conditions. However, the potential of biodegradation as a treatment technology for these compounds hasn't been developed successfully. This thesis focuses on evaluating the biodegradation potential of PFOA and PFOS.

Fluoroacetate dehalogenase is an enzyme capable of defluorinating fluorinated aliphatic compounds. In this study, the potential of fluoroacetate dehalogenaseexpressing microorganisms to biodegrade PFOA and PFOS is examined. Two known fluoroacetate dehalogenase-expressing strains and fluoroacetate-degrading mixed cultures were used. The effect of ammonia in the enzyme activity was extended to study its effect on the biodegradation of PFOA and PFOS. Fluoride ions released during the mineralization of the PFOA and PFOS was used as a proof of biodegradation. The experiments with fluoroacetate dehalogenase-expressing strains and mixed culture consortia enriched from soil showed an increase in fluoride concentration in the solution thus indicating the possibility of successful biodegradation of PFOA and PFOS. Based on the fluoride ion content, it was also concluded that ammonia inhibits the enzyme activity in one of the two pure strains.