4. Discussion Mesotrione is easily and quickly degraded and eluted from thesoil, being transported by rainwater into to the surface water. Nev-ertheless, concentrations of around 1.8 g L−1of mesotrione wasfound in streams next to crop fields [5]. This concentration wastested in our work and did not induced any changes in oxireductiveenzymes in any species. Kreutz et al. [23] evaluated the LC50of theneotropical fish R. quelen to many pesticides, including mesotrione.They found that mesotrione had a lethal concentration higher thanother pesticides. While, the LC50of mesotrione was 532 mg L−1, theLC50 of glyphosate, atrazine and tebuconazole were 7.3, 7.2, and5.3 mg.L−1, respectively.Although mesotrione is easily degradable, its metabolites canpresent toxic effects. The metabolites MNBA (4-methylsulfonyl-2-nitrobenzoic acid) and AMBA (2-amino-4- methylsulfonylbenzoicacid) are found together with the parental compound in bothsoil and water [1]. Bonnet et al. [6] compared the toxicity of atrazine with the mesotrione, they formulated commercialproduct (Callisto®), and its two major metabolites (MNBA andAMBA) in two nontarget microorganisms that are frequently usedin ecotoxicological tests, the eukaryote Tetrahymena pyriformis andthe prokaryote Vibrio fischeri. The results showed that the Callisto®is more toxic to both species in comparison to atrazine, and about