Biodegradation and toxicity of a maize herbicide mixture: mesotrione, nicosulfuron and S-metolachlor

• Published in: Journal of hazardous materials Vol. 354; pp. 42 - 53
• Main Authors: Carles, Louis, Joly, Muriel, Bonnemoy, Frédérique, Leremboure, Martin, Donnadieu, Florence, Batisson, Isabelle, Besse-Hoggan, Pascale
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.07.2018; Elsevier
• Subjects: active ingredients; agricultural land; agricultural soils; Analytical chemistry; Bacillus megaterium; Bacillus megaterium Mes11; biochemical pathways; biodegradation; Chemical Sciences; corn; crops; environmental fate; Environmental Sciences; Herbicide mixture; herbicide mixtures; mesotrione; metabolites; metolachlor; Microbial toxicity; nicosulfuron; prediction; Simultaneous biotransformation; synergism; toxicity; Bacillus megaterium Mes11; Herbicide mixture; Microbial toxicity; Simultaneous biotransformation; Mes11 Microbial toxicity; Bacillus megaterium
• ISSN: 0304-3894; 1873-3336; 1873-3336
• DOI: 10.1016/j.jhazmat.2018.04.045

[Display omitted] •B. megaterium transforms both mesotrione and nicosulfuron, alone or in mixture.•Biotransformation pathways are not affected in binary and ternary mixtures.•Nicosulfuron degradation and metabolite formation kinetics is mixture dependent.•Binary/ternary mixtures of active ingredients show synergistic effects (Microtox®).•Metabolite mixtures ± S-metolachlor show synergism, antagonism or additivity. The prediction of chemical mixture toxicity is a major concern regarding unintentional mixture of pesticides from agricultural lands treated with various such compounds. We focused our work on a mixture of three herbicides commonly applied on maize crops within a fortnight, namely mesotrione (β-triketone), nicosulfuron (sulfonylurea) and S-metolachlor (chloroacetanilide). The metabolic pathways of mesotrione and nicosulfuron were qualitatively and quantitatively determined with a bacterial strain (Bacillus megaterium Mes11). This strain was isolated from an agricultural soil and able to biotransform both these herbicides. Although these pathways were unaffected in the case of binary or ternary herbicide mixtures, kinetics of nicosulfuron disappearance and also of mesotrione and nicosulfuron metabolite formation was strongly modulated. The toxicity of the parent compounds and metabolites was evaluated for individual compounds and mixtures with the standardized Microtox® test. Synergistic interactions were evidenced for all the parent compound mixtures. Synergistic, antagonistic or additive toxicity was obtained depending on the metabolite mixture. Overall, these results emphasize the need to take into account the active ingredient and metabolites all together for the determination of environmental fate and toxicity of pesticide mixtures.