Work

Multi-element (2H, 13C, 37Cl) isotope analysis to characterize reductive transformation of α-, β-, γ-, and δ-HCH isomers by cobalamin and Fe0 nanoparticles

Year: 2024

Type: article

Abstract: Hexachlorocyclohexane (HCH), a typical persistent organic pollutant, poses a serious threat to both human health and the environment. The degradability of HCH isomers (α, β, γ, and δ) varies significantly under anoxic aqueous conditions and the corresponding reductive transformation mechanisms remain elusive. This work employed multi-element ( 2 H, 13 C, 37 Cl) stable isotope analysis to characterize the reductive dehalogenation mechanisms of HCH isomers using cobalamin (vitamin B ₁₂ ) reduced with Ti 3+ and Fe 0 nanoparticles. The isotopic fractionation of HCH isomers varied from −2.8 ± 0.5 to −7.0 ± 0.7 ‰ for carbon (ε C ), from not significant to −62.4 ± 5.2 ‰ for hydrogen (ε H ), and from −1.4 ± 0.2 to −4.7 ± 0.5 ‰ for chlorine (ε Cl ), respectively. Dual C-Cl isotopic fractionation values (Λ C/Cl ) for α-, β-, γ- and δ-HCH during the transformation by B 12 were determined to be 2.0 ± 0.2, 1.5 ± 0.2, 1.1 ± 0.1, and 1.9 ± 0.3, respectively. The Λ C/Cl values of β- and δ-HCH in the reaction with Fe 0 nanoparticles were found to be similar (1.9 ± 0.3 and 1.9 ± 0.2). However, the apparent kinetic isotope effect AKIE C /AKIE Cl values suggested that the bond cleavage mechanism of δ-HCH may differ from that of other isomers. The comparison of the angles θ by multi-element isotope plot showed a distinct differentiation between the pathways of anaerobic transformation of HCH isomers and aerobic pathways reported in the literature. Therefore, multi-element isotope analysis could offer a new perspective for characterizing the fate of HCH isomers. • Dehalogenation of α, β, γ, and δ-HCH by cobalamin reduced by Ti 3+ was studied. • Concerted dichloroelimination is more likely to occur during HCH B 12 and Fe 0 reduction . • Isotopic fractionation (ε) of multi-elements ( 2 H, 13 C, 37 Cl) were assessed. • Secondary H isotopic fractionation was detected during the transformation of HCHs. • ME-CSIA can distinguish between aerobic and anaerobic dehalogenation pathways.

Source: Journal of Hazardous Materials

DOI: 10.1016/j.jhazmat.2024.135932