0000000000432963
AUTHOR
Claire Richard
showing 6 related works from this author
Fluorescence of soil humic acids and their fractions obtained by tandem size exclusion chromatography-polyacrylamide gel electrophoresis
2002
Humic acids (HAs) extracted from soils of different origin (chernozem, ferralsol and ranker) and their fractions (A, B and C+D) obtained by tandem size exclusion chromatography–polyacrylamide gel electrophoresis were investigated by steady-state fluorescence spectroscopy in the emission mode. Independently of HA source, high molecular size fractions A and B are shown to be weakly fluorescent. The main fluorophores, especially those emitting at long wavelength (around 500–510 nm), are contained in the polar and low molecular size fractions C+D. As indicated by the observed pH effect, aromatic structures bearing carboxylate and OH substituents may be involved in these longer wavelength emissi…
Photoinductive efficiency of soil extracted humic and fulvic acids
2002
Humic and fulvic acids extracted from soils of different genesis were investigated for their ability to photoinduce the transformation of fenuron (2 x 10(-4) mol(-1)) at 365 nm. The ratio of the initial rate of fenuron consumption over the rate of light absorption by humic substances was found to be higher for fulvic acids (range 2.0 x 10(-3) to 9.0 x 10(-5)) than for humic acids (range 1.7 x 10(-4) to - 3.6 x 10(-5)). Within the FAs population, this ratio decreased as the specific absorption coefficient at 365 nm increased. It seems therefore that most of 365-nm absorbing components have no photoinductive activity and even reduce that of photoinductive chromophores.
Transformation of monuron photosensitized by soil extracted humic substances: energy or hydrogen transfer mechanism?
1997
The humic and fulvic acids extracted from a Ranker type soil sensitize the transformation of monuron. When monuron is irradiated at 365 nm in the presence of the fulvic acid, its degradation is faster in deoxygenated medium than in air-saturated solution. Chloride ions are released, and the para-hydroxylated derivative is formed as upon direct photolysis. It is deduced that the consumption of monuron observed in the absence of oxygen is due to an energy transfer from reactive triplet states of the fulvic acid to monuron. Energy transfer reactions also take place when hydroquinone or acetophenone are used as sensitizers, showing that the energy level of the triplet state of monuron is lower …
Comparison of the photoinductive properties of commercial, synthetic and soil-extracted humic substances
1997
Abstract The photochemical behavior of a fulvic acid (FA) and several humic acids (HAs) were studied. These synthetic, commercial or soils-extracted humic substances were compared according to their abilities to sensitize the formation of singlet oxygen and to photoinduce the transformation of aromatic compounds such as 2,4,6-trimethylphenol (TMP) and 1,1-dimethyl-3-phenylurea (fenuron). Singlet oxygen was detected by ESR experiments, and quantum yields of singlet oxygen formation were measured by using 1,2-difuranyl-2-hydroxyethanone (furion) as a probe molecule. The photoinductive capacities were evaluated from the kinetics of TMP and fenuron disappearance. The humic substances that showe…
French collective expertise on herbicide-tolerant varieties
2013
The primary objective in creating herbicide-tolerant varieties is to offer the farmers with an efficient tool to ensure weed control and solve weed problems, but their use could eventually have expected or unexpected consequences according to conditions of implementation. A few of those varieties, obtained either through classical breeding or through induced mutagenesis are now on the European market (especially oilseed rape and sunflower) while a majority, which was obtained through genetic engineering, is not allowed for cultivation in this area. The report describes how CNRS and INRA experts dealt with the scientific literature, extracts key elements, points out necessary watchfulness on…
Les variétés végétales tolérantes aux herbicides, un outil de désherbage durable ?
2014
Depuis 2009, des variétés de tournesol et de colza, dites « tolérantes aux herbicides » (TH), font leur apparition en France. Destinées à faciliter le désherbage, ces variétés résistent à un herbicide donné ce qui permet a priori d’appliquer l’herbicide sans risque pour la culture. La culture de telles variétés a suscité une contestation sociale se traduisant par l’arrachage de tournesols TH dénoncés comme « OGM cachés ». Dans ce contexte, les ministères chargés de l’Agriculture et de l’Environnement ont demandé à l’Inra et au CNRS de réaliser un bilan des connaissances disponibles sur l’ensemble des impacts de la culture de ces variétés.