title: Laccase-mediated transformation of triclosan in aqueous solution with metal cations and humic acid.
abstract: Triclosan (TCS) is a broad-spectrum antimicrobial agent that is found extensively in natural aquatic environments. Enzyme-catalyzed oxidative coupling reactions (ECOCRs) can be used to remove TCS in aqueous solution, but there is limited information available to indicate how metal cations (MCs) and natural organic matter (NOM) influence the environmental fate of TCS during laccase-mediated ECOCRs. In this study, we demonstrated that the naturally occurring laccase from Pleurotus ostreatus was effective in removing TCS during ECOCRs, and the oligomerization of TCS was identified as the dominant reaction pathway by high-resolution mass spectrometry (HRMS). The growth inhibition studies of green algae (Chlamydomonas reinhardtii and Scenedesmus obliquus) proved that laccase-mediated ECOCRs could effectively reduce the toxicity of TCS. The presence of dissolved MCs (Mn2+, Al3+, Ca2+, Cu2+, and Fe2+ions) influenced the removal and transformation of TCS via different mechanisms. Additionally, the transformation of TCS in systems with NOM derived from humic acid (HA) was hindered, and the apparent pseudo first-order kinetics rate constants (k) for TCS decreased as the HA concentration increased, which likely corresponded to the combined effect of both noncovalent (sorption) and covalent binding between TCS and humic molecules. Our results provide a novel insight into the fate and transformation of TCS by laccase-mediated ECOCRs in natural aquatic environments in the presence of MCs and NOM.
authors.affiliation: Institute of Organic Contaminant Control and Soil Remediation, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223, USA; School of Resources and Environment, Anhui Agricultural University, Hefei 230036, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Sun
authors.affiliation: Institute of Organic Contaminant Control and Soil Remediation, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Fuxing
authors.initials: F
authors.lastname: Kang
authors.affiliation: Institute of Organic Contaminant Control and Soil Remediation, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Michael Gatheru
authors.initials: MG
authors.lastname: Waigi
authors.affiliation: Institute of Organic Contaminant Control and Soil Remediation, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China. Electronic address: gaoyanzheng@njau.edu.cn.
authors.forename: Yanzheng
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223, USA. Electronic address: qhuang@uga.edu.
authors.forename: Qingguo
authors.initials: Q
authors.lastname: Huang
mesh_terms: D001673:Biodegradation, Environmental / Q000187:drug effects*; D002384:Catalysis / Q000187:drug effects; D002412:Cations / Q000494:pharmacology; D000460:Chlorophyta / Q000254:growth & development; D006812:Humic Substances; D042845:Laccase / Q000378:metabolism*; D008670:Metals / Q000494:pharmacology*; D010084:Oxidation-Reduction / Q000187:drug effects; D014260:Triclosan / Q000378:metabolism* / Q000633:toxicity
chemical_list: D002412:Cations; D006812:Humic Substances; D008670:Metals; D014260:Triclosan; D042845:Laccase
keywords: Coupling; High-resolution mass spectrometry; Humic acid; Laccase; Metal cations; Triclosan