Free-radical-induced oxidative and reductive degradation of N,N'-diethyl-m-toluamide (DEET): Kinetic studies and degradation pathway.

N,N'-Diethyl-m-toluamide (DEET) is widely used as an insect repellent and has therefore been detected as a contaminant in numerous waste and surface waters. In this study we have determined the absolute reaction rate constants of DEET with the hydroxyl radical and the hydrated electron in aqueous solution as (4.95+/-0.18)x10(9) and (1.34+/-0.04)x10(9) M(-1) s(-1), respectively, using pulse radiation. To provide additional information on the radicals formed upon oxidation, transient spectra were measured from 1 to 150 micros, with transient decay rates determined from the time-dependence of the maximum absorption at 330 nm. These data suggest simple decay of the initially formed radical to stable products. Radical-based destruction mechanisms for destruction of DEET are proposed based on the LC-MS determination of the stable compounds produced by 60Co gamma-irradiation of DEET solutions. These data will be useful in evaluating potential advanced oxidation/reduction processes for the control of DEET and understanding its fate and transport in surface water where analogous radical chemistry is operative.