title: Characterization of humins from different natural sources and the effect on microbial reductive dechlorination of pentachlorophenol.
abstract: Humins have been reported to function as an electron mediator for microbial reducing reactions. However, the physicochemical properties and the functional moieties of humins from different natural sources have been poorly characterized. In this study, humins extracted from seven types of soil and from a river sediment were examined on the effect on microbial reductive dechlorination of pentachlorophenol (PCP) and characterized polyphasically. All humins facilitated microbial reductive dechlorination of PCP as electron mediators using formate as carbon source, with different dechlorination rates ranging from 0.99 to 7.63 (μmol Cl-) L(-1) d(-1). The highest rates were observed in humins with high carbon contents, extracted from Andisols containing allophone as major clay. Yields of the humins and the elemental compositions varied among sources. Fourier transform infrared analysis showed that all the humins exhibited similar spectra with different absorbance intensity; these data are indicative of their similar structures and identical classes of functional groups. The electron spin resonance spectra of humins prepared at different pH showed typical changes for the semiquinone-type radicals, suggestive of quinone moieties for the redox activity of the humins. Cyclic voltammetry analysis confirmed the presence of redox-active moieties in all the humins, with the estimated redox potentials in the range of -0.30 to -0.13 V (versus a standard hydrogen electrode), falling into the range of standard redox potential between the oxidation of formate as electron donor and the initial dechlorination of PCP as electron acceptor.
authors.affiliation: Institute of Marine Biology, Ocean College, Zhejiang University, Hangzhou 310058, China; EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan.
authors.forename: Chunfang
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan.
authors.forename: Dongdong
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan.
authors.forename: Zhixing
authors.initials: Z
authors.lastname: Xiao
authors.affiliation: EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan.
authors.forename: Zhiling
authors.initials: Z
authors.lastname: Li
authors.affiliation: EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Suzuki
authors.affiliation: EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan; Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan. Electronic address: a-katayama@esi.nagoya-u.ac.jp.
authors.forename: Arata
authors.initials: A
authors.lastname: Katayama
mesh_terms: D006812:Humic Substances / Q000032:analysis*; D010416:Pentachlorophenol / Q000378:metabolism*; D019800:Phenol / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000378:metabolism*
chemical_list: D006812:Humic Substances; D014874:Water Pollutants, Chemical; C001861:humin; D019800:Phenol; D010416:Pentachlorophenol
keywords: Chemical spectroscopic and electrochemical characterization; Electron mediator; Humin; Microbial reductive dechlorination; Pentachlorophenol