## 3 Degradation and Fate of PFCs in the Environment
### Other Biological Remediation Processes of PFOA and PFOS  
Previously conducted studies have reported on a number of effective remedial technologies of PFCs from aquatic environments, such as photocatalysis and electrochemical oxidation [50, 51, 52, 53], plasma technology [54, 55], and adsorption by granular-activated carbon [15]. However, the aforementioned treatment technologies are energy-intensive, consequently resulting in high operational costs [56]. Hence, this section of the paper focuses on PFOA and PFOS remediation by phytoremediation, characterized as an environmentally green and cost-effective process. The removal of organic pollutants by plants is known as phytoremediation. The mechanism of the phytoremediation process consists of (1) phytofiltration, which is essentially the uptake of pollutants by the plant; (2) phytovolatilization, which is the conversion of pollutants to volatile form; and (3) phytodegradation, which involves the participation of root exudes and microbial population [56]. Early studies [57, 58] have demonstrated that plants can absorb PFCs, where long-chain PFCs are likely to be accumulated in roots, and short chains are more likely to be accumulated in buds, fruits, and crops [15]. [PERSON] et al. [57] investigated the uptake of PFCs by various plant species, and it was reported that high concentrations of short-chain PFCs were detected in leaves, with PFOA and PFOS being detected in roots. It is worth mentioning that [PERSON] et al. [57] did not report on PFOA and PFOS phytovolatilization and phytodegradation. The findings suggest that only phytofiltration was observed for PFOA and PFOS phytoremediation mechanisms. [PERSON] et al. [58] investigated the sorption of PFCs in the water-sediment-plant system along the Dongzhulong and Xiaoqing rivers by floating and rooted plant species. The average PFC concentration in water was reported to be 84,000 ng/L and 2300 ng/L in sediments, respectively, with PFOA accounting for up to 97% in both water and sediment. It was reported that PFOA demonstrated high sorption affinity with floating plant species absorbing a higher concentration of PFCs as compared to rooted plants. The high uptake capacity by floating plants is attributed to large proliferation rates. Higher PFOA concentrations were detected in the roots of plant species for both floating and rooted plant species, suggesting that phytofiltration took place. The PFCs distribution analysis within the model plant species for the work reported by [PERSON] et al. [58] demonstrated that short-chain PFCs were concentrated more in the shoots than in the roots, congruent to the work reported by [PERSON] et al. [57]. Short-chain PFC uptake is attributed to the water potential gradient resulting from plant transpiration, consequently promoting the upward uptake of PFCs through the xylem [58]. On the other hand, the accumulation of long-chain PFCs in plant roots can be attributed to the proteinphilic-linked sorption. Previously undertaken studies on the phytoremediation of PFOA and PFOS suggest that long-chain PFCs are bound strongly to the roots' surface due to a positive correlation with protein content as opposed to short-chain PFCs [58, 59]. The phytoremediation of PFOA and PFOS is strongly dependent on plant species. [PERSON] et al. [59] investigated the role of proteins and lipids in the accumulation of PFOA and PFOS by different plant species, i.e., alfalfa, lettuce, maize, mung bean, radish, ryegrass, and soyabeans. It was reported that the concentration of PFOA and PFOS in the roots of the aforementioned model plant species did not follow the same trend, with ryegrass, maize, and radish roots recording the lowest PFOA and PFOS concentrations. The observed behavior was attributed to the low protein content in the roots of ryegrass, maize, and radish, as reported by [PERSON] et al. [59]. Moreover, it was reported that the binding of PFOS to roots was stronger than that of PFOA; therefore, the transfer potential of PFOA from roots to shoots is more favorable compared to PFOS [59].