Photolysis of the herbicide sulcotrione: formation of a major photoproduct and its toxicity evaluation.
BACKGROUND
Sulcotrione is a selective herbicide marketed for use in maize since 1993, but its environmental fate is not yet fully elucidated. A major metabolite resulting from cleavage between the two ring moieties, leading to 2-chloro-4-mesylbenzoic acid (CMBA), has been identified; it presents a rather low toxicity. In photochemical studies this compound has also been claimed to be formed in high proportions. The present authors recently found that, under irradiation, sulcotrione mainly yields a cyclization product (CP). Thus, Sulcotrione photochemistry is still a matter of debate. The aim of the present work was to give an unequivocal answer to this issue. The potential toxicity of CP, CMBA and sulcotrione towards three organisms considered as representative of aquatic ecosystems was also evaluated.


RESULTS
The main transformation product of sulcotrione is the cyclization product (CP), and CMBA is formed in smaller amounts. For the toxicological approach, the tested organisms were a bacterium, Vibrio fischeri (Bejerinck) Lehmann & Neumann, an alga, Pseudokirchneriella subcapitata (Korshikov) Hindak, and a protozoan, Tetrahymena pyriformis (Ehrenberg) Lwoff. Sulcotrione is more harmful towards the alga, but CP is more toxic to the bacterium and the protozoan. It must be noted that the measured toxicities are nonetheless rather low.


CONCLUSIONS
On irradiation, sulcotrione mainly gives the photocyclization product, which presents a higher toxicity than sulcotrione and CMBA. This cyclization product should thus be considered in sulcotrione environmental risk assessment.
ter Halle
Alexandra
A
Laboratoire de Photochimie Moléculaire et Macromoléculaire, UMR CNRS-UBP 6505, Université Blaise-Pascal, Aubière Cedex, France.
Wiszniowski
Jaroslaw
J
Hitmi
Adnane
A
Ledoigt
Gérand
G
Bonnemoy
Frédérique
F
Bonnet
Jean-Louis
JL
Bohatier
Jacques
J
Richard
Claire
C
D000818:Animals; D001419:Bacteria / Q000187:drug effects; D003512:Cyclohexanones / Q000737:chemistry*; D056890:Eukaryota / Q000187:drug effects; D008698:Mesylates / Q000737:chemistry*; D015394:Molecular Structure; D010782:Photolysis; D013769:Tetrahymena pyriformis / Q000187:drug effects; D018675:Toxicity Tests
D003512:Cyclohexanones; D008698:Mesylates; C079906:sulcotrione