title: On the natural fate of maleic hydrazide. Kinetic aspects of the photochemical and microbiological degradation of the herbicide.
abstract: Kinetic and mechanistic aspects of the photochemical and microbiological degradation of the herbicide Maleic Hydrazide (MH) have been studied. Riboflavin (Rf, vitamin B2) was employed as a main photosensitizer whereas Humic Acid (HA) was included as a second sensitizer in order to more closely simulate natural environmental conditions. MH quenches excited singlet and triplet states of Rf, with rate constants close to the diffusion limit. The herbicide and dissolved molecular oxygen competitively quench triplet excited Rf. As a consequence the reactive oxygen species (ROS), superoxide radical anion (O2(-·)), hydrogen peroxide (H2O2) and singlet molecular oxygen (O2((1)Δg)) are produced by electron- and energy-transfer processes, respectively, as demonstrated by auxiliary experiments employing selective auxiliary quenchers and the exclusive O2((1)Δg) generator Rose Bengal (RB). As a global result, the photodegradation of Rf is retarded, whereas MH is degraded by the generated ROS. The bacteria Pseudomonas aeruginosa (Ps) and Bacillus subtilis (Bs), recognized as contaminants surface-water and soil and microbial antagonists of phytopathogenic, were used in the microbiological experiments. Results of the individual incubation of both bacteria in in the presence of MH indicate a stimulation on the Ps growth, implying the biodegradation of the herbicide, whereas MH only exerted a bacteriostatic effect on Bs.
authors.affiliation: Facultad de Ingeniería, Universidad Nacional de la Patagonia SJB, 9000 Comodoro Rivadavia, Argentina; Unidad Académica Río Gallegos, Universidad Nacional de la Patagonia Austral, 9400 Río Gallegos, Argentina.
authors.forename: Adriana
authors.initials: A
authors.lastname: Pajares
authors.affiliation: Unidad Académica Río Gallegos, Universidad Nacional de la Patagonia Austral, 9400 Río Gallegos, Argentina.
authors.forename: Mabel
authors.initials: M
authors.lastname: Bregliani
authors.affiliation: Departamento de Química, Universidad Nacional de Río Cuarto, 5800 Río Cuarto, Argentina.
authors.forename: Walter
authors.initials: W
authors.lastname: Massad
authors.affiliation: Departamento de Química, Universidad Nacional de Río Cuarto, 5800 Río Cuarto, Argentina.
authors.forename: José
authors.initials: J
authors.lastname: Natera
authors.affiliation: Departamento de Química, Universidad Nacional de Río Cuarto, 5800 Río Cuarto, Argentina.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Challier
authors.affiliation: Facultad Regional Villa María, Universidad Tecnológica Nacional, 5900 Villa María, Argentina.
authors.forename: Laura
authors.initials: L
authors.lastname: Boiero
authors.affiliation: Facultad Regional Villa María, Universidad Tecnológica Nacional, 5900 Villa María, Argentina; Instituto de Ciencias Básicas y Aplicadas, Universidad Nacional de Villa María, 5900 Villa María, Argentina.
authors.forename: Mariana
authors.initials: M
authors.lastname: Montenegro
authors.affiliation: Departamento de Química, Universidad Nacional de Río Cuarto, 5800 Río Cuarto, Argentina. Electronic address: ngarcia@exa.unrc.edu.ar.
authors.forename: Norman A
authors.initials: NA
authors.lastname: García
mesh_terms: D001412:Bacillus subtilis / Q000378:metabolism*; D001673:Biodegradation, Environmental; D004583:Electrons; D004785:Environmental Pollutants / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D006540:Herbicides / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D006812:Humic Substances; D007700:Kinetics; D008300:Maleic Hydrazide / Q000737:chemistry*; D010782:Photolysis; D017319:Photosensitizing Agents / Q000737:chemistry; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000737:chemistry; D012256:Riboflavin / Q000737:chemistry
chemical_list: D004785:Environmental Pollutants; D006540:Herbicides; D006812:Humic Substances; D017319:Photosensitizing Agents; D017382:Reactive Oxygen Species; D012256:Riboflavin; D008300:Maleic Hydrazide
keywords: Biodegradation; Humic acid; Maleic hydrazide; Photodegradation; Riboflavin