Transformation and Removal of Tetrabromobisphenol A from Water in the Presence of Natural Organic Matter via Laccase-Catalyzed Reactions: Reaction Rates, Products, and Pathways

Abstract

The widespread occurrence of the brominated flame retardant tetrabromobisphenol A (TBBPA) makes it a possible source of concern. Our experiments suggest that TBBPA can be effectively transformed by the naturally occurring laccase enzyme from Trametes versicolor. These reactions follow second-order kinetics, whereby apparent removal rate is a function of both substrate and enzyme concentrations. For reactions at different initial concentrations and with or without natural organic matter (NOM), reaction products are identified using liquid or gas chromatography with mass spectrometry. Detailed reaction pathways are proposed. It is postulated that two TBBPA radicals resulting from a laccase-mediated reaction are coupled together via interaction of an oxygen atom on one radical and a propyl-substituted aromatic carbon atom on the other. A 2,6-dibromo-4-isopropylphenol carbocation is then eliminated from the radical dimer. All but one of the detected products arise from either substitution or proton elimination of the 2,6-dibromo-4-isopropylphenol carbocation. Three additional products are identified for reactions in the presence of NOM, which suggests that reaction occurs between NOM and TBBPA radical. Data from acute immobilization tests with Daphnia confirm that TBBPA toxicity is effectively eliminated by laccase-catalyzed TBBPA removal. These findings are useful for understanding laccase-mediated TBBPA reactions and could eventually lead to development of novel methods to control TBBPA contamination.

Ferrate(VI) oxidation of tetrabromobisphenol A in comparison with bisphenol A

“…Initially, Fe(VI) oxidizes the phenol moiety of TBBPA by one electron transfer generating a phenoxyl radical and Fe(V) as the first step (Rush et al, 1995;Huang et al, 2001;Li et al, 2008;Yang et al, 2011b). The phenoxy radical is stabilized by electron resonance within the phenol ring and forms radical R1, which supported by the calculation of charge distribution and spin densities via molecular modeling (Lin et al, 2009;Feng et al, 2013;Pang et al, 2014). Radical R1 undergoes bscission (cleavage between one of the benzene rings and the isopropyl group) and releases a new radical 2,6-dibromo-4-isopropylphenol carbocation (R2).…”

“…The two products A and B had a molecular ion peak at m/z of 308.9 and 322.9 and product ions 290.9, 80.9 and 78.8 (Fig. S6), which were considered as 4-(2-hydroxyisopropyl)-2,6-dibromophenol and 4-(2-methoxylisopropyl)-2,6-dibromophenol, respectively (Feng et al, 2013;Pang et al, 2014). But it should be noted that products A and B were also presented at trace levels in the initial reaction solution (0 s).…”

“…Radical R1 undergoes bscission (cleavage between one of the benzene rings and the isopropyl group) and releases a new radical 2,6-dibromo-4-isopropylphenol carbocation (R2). R2 may react with water to form the product A, or substitution with the methanol cosolvent (stock solution was prepared in methanol) to yield the product B (Feng et al, 2013). The pathway of product A has been extensively reported in the oxidative degradation of TBBPA by permanganate, manganese dioxide, UV/Fenton, and UV irradiation (Eriksson et al, 2004;Lin et al, 2009;Zhong et al, 2012;Pang et al, 2014).…”

Recent advances in the analysis of TBBPA/TBBPS, TBBPA/TBBPS derivatives and their transformation products

“…For the cleanup of nonwater samples, the most widely used methods were gel permeation chromatography (GPC), activated silica gel column, and Florisil [6,31]. Commercially available SPE tubes also have good applicability for the cleanup of residues extracted from soil, sediment, [14][15][16][17][18][19][20][21][22][23][24] and biota samples [32]. However, severalcommercial cartridges showed poor recoveries because target analytes were strongly absorbed by the sorbents of the cartridges and could not be adequately eluted [10].…”

“…Cumulative evidence suggests that abiotic degradation, including photolysis, oxidation, reduction, and radical reactions, are involved in TBBPA degradation [14][15][16]. As compared with abiotic reactions, biotic reactions are considered to be the main transformation pathways of TBBPA and can result in the presence of unknown brominated substances in environmental compartments [8,17,18]. With the development of analytical methods based on MS, various transformation products of TBBPA have been observed [8,9,[15][16][17][18][19][20][21].…”