Abiotic transformation of chlorinated organics at the active surface of iron-bearing minerals in soils and sediments

Abstract

Chlorinated organic compounds are emerging pollutants of widespread concern because of their toxicity, bioaccumulation, persistence, and lack of adequate regulatory measures. Their abiotic transformation, facilitated by iron-bearing minerals, is critical to their natural dissipation in soils and sediments. However, further exploration is needed to understand their underlying mechanisms and potential engineering applications under different redox conditions. This paper reviews the abiotic transformation behaviors and mechanisms of chlorinated organics at the active surface of iron-bearing minerals under anoxic and oxic conditions and summarizes the strategies for enhancing the abiotic transformation efficiency of chlorinated organics. The abiotic transformation rate under oxic conditions can be a few orders of magnitude higher than that under anoxic conditions. Under anoxic conditions, chlorinated organics undergo reductive dechlorination through reductive elimination, hydrogenolysis, dehydrohalogenation, and nucleophilic substitution. A close relationship between the abiotic transformation of chlorinated organics and the production of hydroxyl radicals by iron-bearing minerals under oxic conditions was discovered. Synthetic active iron-bearing minerals, carbonaceous materials, and biological synergy can facilitate abiotic dechlorination under anoxic conditions. Meanwhile, the regulation of redox conditions, the introduction of ligands, and the utilization of coexisting anions are proposed to enhance oxidative degradation. This study is expected to improve the comprehension of the abiotic degradation of chlorinated organics mediated by iron-bearing minerals and provide the theoretical foundation for developing new approaches aimed at addressing chlorinated organic pollution.