## 3 Degradation and Fate of PFCs in the Environment
### Bacterial Biodegradation
Despite the chemically challenging C-F bond cleavage, recently performed studies have demonstrated that PFCs, particularly PFOA and PFOS, can be defluorinated by strong chemical oxidants, as well as by microbial population [39; 40; 41]. Many researchers have reported limited microbial defluorination of PFCs. This is attributed to the displacement of C-F bonds, which yield a fluoride ion, F-, that is toxic to microbial population at minute concentrations [42]. The fluoride ion, which is produced as a result of PFCs' biodegradation (i.e., defluorination), enters bacterial cells, thus poisoning them [41; 42]. The poisoning of bacterial cells ceases or hinders metabolic activities, resulting in the nonbiodegradability of PFCs. Such a biological reaction mechanism explains why fluorine concentrations are not detected during biodegradation of PFCs. The revelation of the toxicity of the fluoride ion to bacterial cells explains why PFCs are characterized as xenobiotic compounds. Moreover, the biodegradation mechanism of PFCs suggests that their xenobiotic characteristics are not solely a result of the C-F bond, but it can be attributed to the toxicity of the fluoride ion which hinders microbial activities. Recently, [PERSON] and [PERSON] [40] demonstrated that PFOA and PFOS are susceptible to biodegradation by _Acidimicrobium_ sp. strain A6 (an autotroph) that oxidizes ammonium to nitrite while reducing ferric iron. Both PFOA and PFOS were added as carbon sources during the oxidation of ammonium to nitrite, while reducing ferric iron by _Acidimicrobium_ in an anaerobic environment. It was reported that both PFOS and PFOA were metabolized recording a removal efficiency of up to 60% for both PFOS and PFOA over an incubation period of 100 days. Despite the observed biodegradation of PFOS and PFOA, it was reported that intermediate products, such as perfluorobutanoic acid, perfluoroheptanoic acid, perfluoroheptanoic acid, and perfluorohexanoic acid, were detected in _Acidimicrobium_ culture. The aforementioned intermediate products were detected for PFOA and PFOS initial concentrations of 100 mg/L. It is also worth mentioning that the initial concentration of 100 mg/L for the model PFCs was detrimental to the microbial population. A significant decline on _Acidimicrobium_ population was observed from day 60 of incubation, as compared to an initial concentration of 0.1 mg/L. Moreover, the findings reported by [PERSON] and [PERSON] [40] suggests that PFOS is more detrimental to _Acidimicrobium_ population, as compared to PFOA. Hitherto, there is no available literature reporting on PFOA and/or PFOS optimum concentration aimed at minimizing their detrimental effects on microbial population. [PERSON] et al. [43] investigated the biodegradation of PFOA in microbial electrolysis cells using _Acidimicrobium_ sp. strain A6 as an inoculum under anaerobic conditions. It was reported that a decrease in PFOA concentration was observed after 18 days of operation, while producing electricity. For the work reported by [PERSON] and co-workers, the biodegradation of PFOA is not explicitly accounted for, on the basis that no PFOA measurements were conducted during operation but FFOA degradation intermediate products analogous to the one reported by [PERSON] and [PERSON] [40] were detected. The measurement of PFOA intermediate products is attributed to the complexities of PFOA measurements, which can be affected by sample handling and hemimicelle formation [43]. For the work reported by [PERSON] et al. [43], 100 mg PFOA/L was the desired initial concentration; however, due to hemimicelle formation, the initial concentration measured was 47 mg PFOA/L. Due to the recalcitrance and high stability of PFCs, particularly PFOA and PFOS, researchers have continued to test various microbial species aimed at testing their ability to biodegradable the aforementioned model contaminants. To the best of our knowledge, apart from _Acidimicrobium_ sp.