Ozonation of chlorophenylurea pesticides in water: reaction monitoring and degradation pathways.
The degradation of mono- and dichlorophenylureas under ozone/hydrogen peroxide conditions was investigated in order to establish the effect of the structural parameters. The N-dimethyl phenylureas (mono- and dichloro) appear to differ strongly from the corresponding N-methyl N-methoxy analogues in terms of disappearance of the parent pesticide and evolution of the by-products identified by MS and MS-MS. The degradation rate of the latter is slower by a factor of 2.5 giving rise to additional pathways (hydroxylation of the phenyl ring and carbinolamine intermediate). Experiments with 14C-labelled compounds allow a complete determination of the mass balances obtained after solid-phase-extraction (SPE). This study demonstrates the interest of SPE for reaction monitoring and compares the performances of different types of phases for this purpose used alone or in combination. Mineralisation is also evaluated regarding 14CO2 production and found to contribute up to 20% in the degradation process.