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| Laccase-induced self-polymerization of estrogens: effect of humic acid on transformation kinetics |
| Received:September 22, 2022 |
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| KeyWord:humic acid;fungal laccase;estrogen;polyreaction;influencing mechanism |
| Author Name | Affiliation | E-mail | | GAO Xi | Suzhou Sentech Environmental Remediation Company Limited, Suzhou 215104, China | | | CHEN Meihua | Anhui Province Key Laboratory of Farmland Ecological Conservation and Pollution Prevention, College of Resources and Environment, Anhui Agricultural University, Hefei 230036, China | | | SUN Kai | Anhui Province Key Laboratory of Farmland Ecological Conservation and Pollution Prevention, College of Resources and Environment, Anhui Agricultural University, Hefei 230036, China | sunkai@ahau.edu.cn |
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| Abstract: |
| Laccase is capable of catalyzing the one-electron oxidation of estrogens to produce macromolecular polymers, using dissolved O2 in water as the final electron acceptor. Presently, little information is available regarding the effects of humic acid(HA) on laccaseinduced estrogen self-polymerization. In this study, we selected 17β-estradiol(E2), 17α-ethinylestradiol(EE2), and bisphenol A(BPA) as three representative environmental estrogens. The effects of HA on the laccase-induced estrogen transformation kinetics, product distribution, and mechanisms were all systematically investigated. The results of this indicated that the removal efficiencies of the three estrogens by laccase were greater than 95% within 3 h, and that the transformation kinetic constants(k) of E2, EE2, and BPA were 2.48, 2.03 h-1, and 1.45 h-1, respectively. HA effectively inhibited laccase-started E2(k=1.04 h-1) and EE2 conversion(k=0.64 h-1), whilst promoting the removal of BPA(k=3.13 h-1). This was likely because laccase-induced HA and BPA co-polymerization rapidly reduced the yields of long-chain BPA self-polymers, thus eliminating their inhibition of catalytic activity and the stability of laccase. Product identification confirmed that the transformation products of the three estrogens were mainly dimers, trimers, tetramers, and oligomers. The co-polymerization mechanisms of estrogen and HA involved two steps here:Firstly, estrogen and HA were oxidized by laccase, which formed many active free radical intermediates. Subsequently, these unstable radical intermediates were covalently bound by C-C, C-O-C, or C-N-C bonds to generate estrogenic self/co-polymeric products. These findings uncover the co-polymerization mechanisms of estrogen-HA induced by laccase and provide a theoretical basis for eliminating estrogen contamination and sequestrating organic carbon based on enzymatic polymerization. |
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