Chlorination of the β-triketone herbicides tembotrione and sulcotrione: Kinetic and mechanistic study, transformation products identification and toxicity

• Published in: Water research (Oxford) 2015-06, Vol.76, p.132-142
• Main Authors: Tawk, Alice, Deborde, Marie, Labanowski, Jérôme, Gallard, Hervé
• Format: Article
• Language: English
• Subjects: Aliivibrio fischeri - drug effects; Chemical Sciences; Chlorination; Chlorine; Chlorine - chemistry; Chloroform; Cyclohexanones - chemistry; Cyclohexanones - toxicity; Disinfectants - chemistry; Halogenation; Herbicides - chemistry; Herbicides - toxicity; Hydrogen-Ion Concentration; Hypochlorous Acid - chemistry; Kinetic; Kinetics; Mesylates - chemistry; Mesylates - toxicity; Organic chemistry; Rate constants; Reaction kinetics; Sulcotrione; Sulfones - chemistry; Sulfones - toxicity; Tembotrione; Toxicity; Transformations; Vibrio; Vibrio fischeri; Water Pollutants, Chemical - chemistry; Water Pollutants, Chemical - toxicity; Water Purification - methods; β-triketones
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2015.02.060

The fate of tembotrione (TBT) and sulcotrione (SCT) during chlorination was investigated in this work. Chlorination kinetics of TBT and SCT were studied by using a continuous-flow reactor in the pH range 2–12 with an excess of total chlorine. Second-order reaction was observed and rate constants of 9.69 (±0.15) × 103 M−1s−1 for TBT and 9.48 (±0.62) × 103 M−1s−1 for SCT were obtained at pH 7. Intrinsic rate constants for the elementary reactions of chlorine species with neutral and deprotonated forms of TBT and SCT were also calculated, leading to the conclusion that the reaction between hypochlorous acid and the deprotonated form of the pesticide is predominant at neutral pH. Several degradation products during chlorination of TBT and SCT were identified by LC-MS/MS and a reaction pathway was proposed. Chlorine initially reacted on the α-carbon of the three carbonyl functional groups. This reaction initiated the well-known haloform reaction and produced chloroform as end-product. Molar yields of 0.99 mol CHCl3/mol and 0.91 mol CHCl3/mol were obtained for TBT and SCT, respectively at pH 7. Moreover, a toxicity evaluation using Vibrio fischeri was carried out to study the toxicity pattern during TBT and SCT chlorination. An increase in toxicity was observed but it could not be clearly assigned to the identified byproducts. [Display omitted] •Reaction between chlorine and β-triketones occurs within a few seconds.•Initial products would be more toxic than parent compound against Vibrio Fischeri.•Chloroform and glutaric acid are produced as end-products.