Ionizing radiation induced degradation of monuron in dilute aqueous solution

The decomposition of monuron was investigated in dilute aqueous solutions using pulse radiolysis and gamma-radiolysis in order to identify the intermediates and final products. The main reaction takes place between monuron and the hydroxyl radicals yielding hydroxycyclohexadienyl type radicals with a second order rate constant of (7.4 +/- 0.2) x 10(9) mol(-1) dm(3) s(-1). In (OH)-O-center dot reactions, the aminyl and phenoxyl radicals may also form. Dechlorination was observed in both hydroxyl radical and hydrated electron reactions. The (OH)-O-center dot induced dechlorination reactions are suggested to occur through OH substitution or phenoxyl radical formation. The rate of oxidation is very high in the presence of dissolved oxygen. Some of the results are also supported by quantum chemical calculations. (C) 2015 Elsevier Ltd. All rights reserved.