Reductive Hexachloroethane Degradation by S<sub>2</sub>O<sub>8</sub><sup>•–</sup> with Thermal Activation of Persulfate under Anaerobic Conditions ZhuChangyin ZhuFengxiao LiuCun ChenNing ZhouDongmei FangGuodong GaoJuan 2018 Despite that persulfate radical (S<sub>2</sub>O<sub>8</sub><sup>•–</sup>) is an important radical species formed from the persulfate (PS) activation process, its reactivity toward contaminant degradation has rarely been explored. In this study, we found that S<sub>2</sub>O<sub>8</sub><sup>•–</sup> efficiently degrades the contaminant hexachloroethane (HCA) under anaerobic conditions, whereas HCA degradation is negligible in the presence of oxygen. We observed dechlorination products such as pentachloroethane, tetrachloroethylene, and Cl<sup>–</sup> during HCA degradation, which suggest that HCA degradation is mainly a reductive process under anaerobic conditions. Using free radical quenching and electron paramagnetic resonance (EPR) experiments, we confirmed that S<sub>2</sub>O<sub>8</sub><sup>•–</sup> forms from the reaction between sulfate radical (SO<sub>4</sub><sup>•–</sup>) and S<sub>2</sub>O<sub>8</sub><sup>2–</sup>, which are the dominant reactive species in HCA degradation. Density functional theory (DFT) calculations were used to elucidate the pathways of HCA degradation and S<sub>2</sub>O<sub>8</sub><sup>•–</sup> radical decomposition. Further investigation showed that S<sub>2</sub>O<sub>8</sub><sup>•–</sup> can efficiently degrade HCA and DDTs in soil via reduction during the thermal activation of PS under anaerobic conditions. The finding of this study provide a novel strategy for the reductive degradation of contaminant when PS-based in situ chemical oxidation used in the remediation of soil and groundwater, particularly those contaminated with highly halogenated compounds.