Abstract 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 (\documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} $$^\bullet{\rm OH}$$ \end{document}) 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 favor...