title: Aerobic biodegradation of amphoteric amine-oxide-based surfactants: Effect of molecular structure, initial surfactant concentration and pH.
abstract: The present study was designed to provide information regarding the effect of the molecular structure of amphoteric amine-oxide-based surfactants and the initial surfactant concentration on their ultimate biodegradation. Moreover, given this parameter's pH-dependence, the effect of pH was also investigated. Three amine-oxide-based surfactants with structural differences in their hydrophobic alkyl chain were tested: Lauramine oxide (AO-R12), Myristamine oxide (AO-R14) and Cocamidopropylamine oxide (AO-Cocoamido). We studied the ultimate biodegradation using the Modified OECD Screening Test at initial surfactant concentrations ranged from 5 to 75 mg L-1and at pH levels from 5 to 7.4. The results demonstrate that at pH 7.4, amine-oxide-based surfactants are readily biodegradable. In this study, we concluded that ω-oxidation can be assumed to be the main biodegradation pathway of amine-oxides and that differences in the biodegradability between them can be explained by the presence of an amide group in the alkyl chain of AO-Cocoamido; the CN fission of the amide group slows down their mineralization process. In addition, the increase in the concentration of the surfactant from 5 to 75 mg L-1resulted in an increase in the final biodegradation of AO-R12and AO-R14. However, in the case of AO-Cocoamido, a clear relationship between the concentration and biodegradation cannot be stated. Conversely, the biodegradability of AO-R12and AO-R14was considerably lower in an acid condition than at a pH of 7.4, whereas AO-Cocoamido reached similar percentages in acid conditions and at a neutral pH. However, microorganisms required more time to acclimate.
authors.affiliation: Department of Chemical Engineering, Faculty of Science, University of Granada, Campus Fuentenueva s/n, 18071, Granada, Spain. Electronic address: rios@ugr.es.
authors.forename: Francisco
authors.initials: F
authors.lastname: Ríos
authors.affiliation: Department of Chemical Engineering, Faculty of Science, University of Granada, Campus Fuentenueva s/n, 18071, Granada, Spain.
authors.forename: Manuela
authors.initials: M
authors.lastname: Lechuga
authors.affiliation: Department of Chemical Engineering, Faculty of Science, University of Granada, Campus Fuentenueva s/n, 18071, Granada, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Fernández-Serrano
authors.affiliation: Department of Chemical Engineering, Faculty of Science, University of Granada, Campus Fuentenueva s/n, 18071, Granada, Spain.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Fernández-Arteaga
mesh_terms: D000332:Aerobiosis; D000588:Amines / Q000737:chemistry*; D001673:Biodegradation, Environmental; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D010087:Oxides / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D000588:Amines; D010087:Oxides; D013501:Surface-Active Agents
keywords: Aerobic biodegradation; Amine-oxide-based surfactants; Amphoteric surfactants; Biodegradability; Modified screening test; pH