title: Enhanced inactivation of Bacillus subtilis spores during solar photolysis of free available chlorine.
abstract: Aqueous free available chlorine (FAC) can be photolyzed by sunlight and/or artificial UV light to generate various reactive oxygen species, including HO(•) and O((3)P). The influence of this chemistry on inactivation of chlorine-resistant microorganisms was investigated using Bacillus subtilis endospores as model microbial agents and simulated and natural solar radiation as light sources. Irradiation of FAC solutions markedly enhanced inactivation of B. subtilis spores in 10 mM phosphate buffer; increasing inactivation rate constants by as much as 600%, shortening inactivation curve lag phase by up to 73% and lowering CTs required for 2 log10 inactivation by as much as 71% at pH 8.0 and 10 °C. Similar results were observed at pH 7.4 and 10 °C in two drinking water samples with respective DOC concentrations and alkalinities of 0.6 and 1.2 mg C/L and 81.8 and 17.1 mg/L as CaCO3. Solar radiation alone did not inactivate B. subtilis spores under the conditions investigated. A variety of experimental data indicate that the observed enhancements in spore inactivation can be attributed to the concomitant attack of spores by HO(•) and O3, the latter of which was found to accumulate to micromolar concentrations during simulated solar irradiation of 10 mM phosphate buffer (pH 8, 10 °C) containing [FAC]0 = 8 mg/L as Cl2.
authors.affiliation: Department of Civil and Environmental Engineering, University of Washington , 201 More Hall, Box 352700, Seattle, Washington 98195, United States.
authors.forename: Jenna E
authors.initials: JE
authors.lastname: Forsyth
authors.forename: Peiran
authors.initials: P
authors.lastname: Zhou
authors.forename: Quanxin
authors.initials: Q
authors.lastname: Mao
authors.forename: Shelby S
authors.initials: SS
authors.lastname: Asato
authors.forename: John S
authors.initials: JS
authors.lastname: Meschke
authors.forename: Michael C
authors.initials: MC
authors.lastname: Dodd
mesh_terms: D001412:Bacillus subtilis / Q000502:physiology / Q000528:radiation effects*; D002713:Chlorine / Q000528:radiation effects*; D006863:Hydrogen-Ion Concentration; D050296:Microbial Viability / Q000528:radiation effects*; D016877:Oxidants / Q000737:chemistry; D010782:Photolysis / Q000528:radiation effects*; D017382:Reactive Oxygen Species / Q000032:analysis; D013171:Spores, Bacterial / Q000502:physiology / Q000528:radiation effects*; D013472:Sunlight; D013696:Temperature; D014871:Water Microbiology
chemical_list: D016877:Oxidants; D017382:Reactive Oxygen Species; D002713:Chlorine