Enhanced Degradation of Deltamethrin in Water through Ferrous Ion Activated Sulfite: Efficiency and Mechanistic Insights

Abstract

Deltamethrin’s global use as a potent insecticide against pests is well-established. However, the compound’s diverse levels of toxicity are increasingly under scrutiny, drawing significant attention to treatments of deltamethrin. Transition metal activation of sulfite is a promising technology for micropollutant degradation. In this study, iron-activated sulfite was used for the degradation of deltamethrin. The degradation effects and influencing factors and the underlying mechanism of deltamethrin degradation in the system were investigated. The degradation of deltamethrin was effectively achieved by the Fe (III)/sulfite system. The optimal reaction conditions at laboratory scale were determined to be an initial pH of 4, a Fe (III) concentration of 100 μM, and a HSO3− concentration of 1 mM, where the degradation rate was approximately 69.5%. Dissolved oxygen was identified as an essential factor in the reaction process, with the degradation rate of deltamethrin decreasing by up to 22% under anaerobic conditions. The presence of light facilitated the degradation of deltamethrin within the reaction system, while bicarbonate and natural organic compounds were found to inhibit its degradation. Quenching experiments verified the presence of hydroxyl radicals (HO•) and sulfate radicals (SO4•−) in the reaction system, with HO• being the predominant species. This was further confirmed by EPR experiments. Additionally, density functional theory calculations indicated the propensity for bond breaking between C16 and O21 in deltamethrin molecules, and the degradation pathway was validated through GC-MS analysis of the products formed. Moreover, the Fe (III)/sulfite system demonstrated good degradation performance for deltamethrin in secondary effluent, achieving degradation rates of 46.3%. In particular, the Fe (III)/sulfite system showed minimal bromate formation, attributed to the capacity of sulfite to reduce active bromine intermediates into bromine ions.