## 4 Conclusions  
This study verifies the utility of CP as a PFOS degradation system and demonstrates the rapidity with which CP removes unwanted PFOS. After 1 h of exposure, PFOS's removal efficiency was 62.5%, which is similar to the removal efficiency seen after 10 h of CP exposure. This similarity is hypothesized to be due to the presence of PFOS degradation intermediates. The kinetic constant obtained by regression was 3.09 h\({}^{-1}\), while CP's superiority over alternative AOPs was further demonstrated by their degradation rate constants. CP-induced PFOS degradation was confirmed by measuring the sulfate and fluoride concentrations in the solution. Acute toxicity testing with _Daphnia magna_ illustrated the relationship between toxicity and PFOS degradation, showing that the degradation intermediates may have a higher toxicity than PFOS itself. This supports the theory that PFOS intermediates act as scavengers, causing incomplete PFOS degradation. Notably, although aeration-assisted cold plasma is known to generate reactive species such as NOx, H\({}_{2}\)O\({}_{2}\), and O\({}_{3}\), our results revealed that the levels of NO3\({}^{-}\) and NO2\({}^{-}\) remained unchanged during CP exposure, indicating that the observed toxicity variations are primarily attributed to the degradation intermediates rather than these reactive species.  
Additionally, when considering the electrical cost of PFOS degradation, CP was confirmed to be a cost-effective option. The rapid decomposition of PFOS by CP was attributed to its rapid formation of hydroxyl radicals. Ultimately, these results suggest that CP technology is a viable physico-chemical option for mineralizing non-biodegradable and ecotoxic PFOS.  
This study illustrates the superiority of CP as a remediation method compared to alternative AOPs, based on their degradation rate constants. Acute toxicity testing reveals how PFOS's toxicity is altered by CP, and the relationship between this and CP's PFOS removal efficiency is discussed. The results suggest that CP technology may be a viable physico-chemical option for mineralizing non-biodegradable, problematic, and ecotoxic PFOS.  
S.O.: Data curation, Formal analysis, Writing--original draft; J.-Y.N.: Conceptualization, Data curation, Formal analysis, Methodology, Writing--original draft; Y.H.: Investigation, Resources, Validation, Visualization; T.-H.L.: Data curation, Resources, Software, Validation, Visualization; H.-W.K.: Conceptualization, Funding acquisition, Investigation, Project administration, Supervision, Writing--review and editing; J.-C.L.: Conceptualization, Investigation, Supervision, Writing--original draft, Writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This paper was supported by research funds from Jeonbuk National University in 2023. This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (no. 2022R1F1A1073198) and a research grant from the project BK21 FOUR. The authors are grateful for the financial support from the 2023 Research Development Program at the Jeonbuk Green Environment Center (grant no. 23-04-50-52-09) and the R&D grant given by the Jeonbukdo business agency. This study was also supported by the Korean Ministry of Environment (MOE) as a Waste-to-Energy Recycling Human Resource Development Project (grant no. YL-WE-23-001).  
Not applicable.