Photochemical Fate of Amicarbazone in Aqueous Media: Laboratory Measurement and Simulations

Amicarbazone (AMZ) is an extensively used, broad-spectrum triazolinone herbicide. The literature is scarce regarding experimental data on AMZ photodegradation, whose fate in natural waters has not yet been investigated in detail. By combining laboratory experiments using isolated natural organic matter, literature data, and mathematical simulations, we investigated the sunlight-driven direct and indirect degradation of AMZ. We show that the reaction with hydroxyl radicals () is the main pathway leading to AMZ degradation, with measured second-order reaction rate constant (kAMZ, OH) equal to 2.05×1010 L/mol·s. Simulations suggest that amicarbazone degradation is favored in shallow water bodies containing low dissolved organic carbon (DOC) and bicarbonate/carbonate concentrations, with herbicide half-life varying from about less than 1 day to more than 2 months. These values of t1/2 are upper limits since the reaction with 3CDOM* was not considered. Finally, the cross-effects of water depth/[DOC] are slightly influenced by nitrate/nitrite and bicarbonate/carbonate concentrations, depending on the pH range.