Sequential bio- and phototransformation of the herbicide methabenzthiazuron in water.
We investigated the transformation of methabenzthiazuron in water by microorganisms and solar light. This compound was very slowly phototransformed when irradiated at lambda > 290 nm, but it could be successfully oxidized into 6-hydroxymethabenzthiazuron by Aspergillus niger, as shown by nuclear magnetic resonance experiments. The toxicity of this metabolite, as determined by the standardized Microtox test, was sixfold lower than that of the parent molecule. The 6-hydroxymethabenzthiazuron was not further metabolized by A. niger but was photooxidized with ring cleavage of the aromatic ring and photodimerized on irradiation at lambda > 290 nm. In the presence of humic substances, the photodegradation was slower. We demonstrate that the transformations of methabenzthiazuron, observed either with the fungus A. niger or by the action of solar light, do not proceed via the urea chain N-dealkylation, as usually reported, but only via hydroxylation or cleavage of the benzene ring. This work shows the complementarity of both approaches, photo- and biodegradation, to study the fate of herbicides in the environment.
Malouki
Moulay Abderrahmane
MA
Laboratoire de Photochimie Moléculaire et Macromoléculaire, UMR 6505 du CNRS, Université Blaise Pascal, 63177 Aubière Cedex, France.
Giry
Géraldine
G
Besse
Pascale
P
Combourieu
Bruno
B
Sancelme
Martine
M
Bonnemoy
Frédérique
F
Richard
Claire
C
Delort
Anne-Marie
AM
D001234:Aspergillus niger / Q000502:physiology*; D052160:Benzothiazoles; D001673:Biodegradation, Environmental; D008782:Methylurea Compounds / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity*; D010084:Oxidation-Reduction; D010777:Photochemistry; D013472:Sunlight; D018675:Toxicity Tests; D014733:Vibrio; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism / Q000633:toxicity*
D052160:Benzothiazoles; D008782:Methylurea Compounds; D014874:Water Pollutants, Chemical; C011912:methabenzthiazuron