## 3 Degradation and Fate of PFCs in the Environment  
### Bacterial Biodegradation  
Conventional WWTPs use biological techniques to treat water and wastewater streams for reuse. During biological treatment of aqueous streams, biodegradable material consisting of organics in dissolved form, such as starches, alcohols, acids, aldehydes, and esters, are utilized for food by microorganisms, thus decontaminating aqueous streams. It is worth noting that microbial utilization of dissolved organics can be accompanied by oxidation, which is the deletion of hydrogen from elements of an organic molecule, or by reduction, which is the addition of hydrogen to elements of the organic molecule [35]. However, a number of previously performed studies suggests that the biodegradation pathways and fate of PFCs are unknown to a large extent. This is attributed to the general belief that the strength of the C-F bond is the limiting factor on PFC biodegradability. However, early evidence suggests that organohalogen compounds, including PFCs, are susceptible to microbial degradation, despite their high stability, as reported by [PERSON] et al. [36]. The biodegradation of organohalogen compounds and PFCs are relatively slow due to their kinetic stability because of the carbon-halogen bond, thus contributing significantly to their long-term environmental fate. Hitherto, dehalogenation is the thermodynamically recognized reaction mechanism for the degradation of organohalogen compounds. Early studies [36; 37] suggest that under aerobic conditions, organohalogen compounds are degraded by catabolic pathways similar to those for nonhalogenated analogues. There are a number of dehalogenation mechanisms that are reported in the literature for both aliphatic and aromatic substrates, i.e., haloacid dehalogenation, halohydrin dehalogenation, haloalkane dehalogenation, and reductive dehalogenation [36]. However, there is very little information reported on the degradation of PFCs, particularly PFOA and PFOS. This is attributed to the biodegradation mechanism \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Regulatory Body** & **PFC** & **Advisory Level, ng/L** & **Toxicological Endpoint** & **Reference** \\ \hline \multirow{2}{*}{U.S. EPA, 2016, Health Advisory Level} & PFOA & 70 & Developmental \\ \cline{2-5}  & PFOS & 70 & Reduced pup body weight \\ \hline \multirow{2}{*}{Alaska DEC 1, 2016, ground water} & PFOA & 400 & Developmental \\ \cline{2-5}  & PFOS & 400 & Reduced pup body weight \\ \hline \multirow{2}{*}{Maine DEP 2, 2016, Remedial action guideline} & PFOA & 130 & Liver \\ \cline{2-5}  & PFOS & 560 & Thyroid effects \\ \hline \multirow{2}{*}{New Jersey DEP, 2017, Maximum contaminant level} & PFOA & 14 & Liver \\ \cline{2-5}  & PFOS & 13 & Immune response \\ \hline \multirow{2}{*}{German Drinking Water Commission} & PFOA & 1500 & N/A \\ \cline{2-5}  & PFOS & 600 & N/A \\ \hline \multirow{2}{*}{Drinking water inspectorate, UK} & PFOA & \textgreater{}300 & N/A \\ \cline{2-5}  & PFOS & \textgreater{}300 & N/A \\ \hline \hline \end{tabular} \({}^{1}\) DEC, Department of Environmental Conservation; 2 DEP, Department of Environmental Protection.  
\end{table} 
Table 2: PFOA and PFOS drinking water guideline levels. of 8:2 fluorotelomer alcohol by OH radicals, which yields PFOA and other perfluorinated carboxylic acids as products [36]. Fluorotelomer alcohols have been reported to biodegradable under aerobic and anaerobic environments [36]. In an early study conducted by [PERSON] and [PERSON] [38], it was demonstrated that both PFOA and PFOS are xenobiotic under aerobic environments. Despite the observed removal of PFOA and PFOS under anaerobic environments, no fluoride ion concentration was detected, which results in the biodegradability mechanism of PFOA and PFOS in aquatic environments remaining difficult to understand for many researchers. In the subsequent section, the biodegradation of PFOA and PFOS are explained, indicating that their xenobiotic characteristics are something of the past.