Oxidative Coupling of 2,6-Dichlorophenol in Three Typical Zonal Soils
The oxidative transformation of 2,6-dichlorophenol (2,6-DCP) was investigated in three typical zonal soils: black soil, red soil, and brown soil. Results demonstrated that 2,6-DCP underwent oxidative coupling in all soils, yielding hydroxylated polychlorinated diphenyl ethers (OH-PCDEs) and hydroxylated polychlorinated biphenyls (OH-PCBs) as primary products. The highest oxidative efficiency occurred in black soil, with approximately 85.1% of 2,6-DCP transformed within three days. In contrast, red and brown soils exhibited lower efficiencies, indicating a strong dependence on soil properties. Thermodynamic analysis revealed that the oxidative coupling reaction is endothermic, with elevated temperatures favoring reaction progress. Furthermore, soil microorganisms and dissolved oxygen were identified as critical controlling factors, acting synergistically to drive the reaction. This study provides the first evidence of natural oxidative coupling of 2,6-DCP in soil, forming OH-PCDEs and OH-PCBs. These findings offer significant scientific insight into the environmental fate of halogenated phenolic pollutants in terrestrial systems.