By-products formation during degradation of isoproturon in aqueous solution. I: Ozonation

The degradation of the herbicide isoproturon during its ozonation in aqueou s solution has been investigated with the aim of identifying intermediate a s well as final by-products formed. Ar ambient temperature, phosphate-buffe red (pH = 7) isoproturon aqueous solutions (10, 10(-1) and 10(-3) mg/l) wer e ozonated in a semi-batch reactor, under a continuous flow of ozonated air whose ozone concentration was 9 and 0.9 O-3/l(air),for the highest and the two lower herbicide concentrations respectively. Measured steady-state ozo ne concentrations during the two sets of experiments (i.e. the highest and the lower isoproturon concentration) were 1.9 and 0.7 mg O-3/l. Under all o f the above conditions. isoproturon was always completely removed in a peri od ranging between 5 and 15 min, essentially by reacting with molecular ozo ne. High-performance liquid chromatography-mass spectrometry (HPLC-MS) anal yses indicate that primary degradation by-products are formed either by int roducing OH groups in the aromatic ring and/or in the side-chain substituen ts. or by breaking down the isopropyl alkyl chain. The results also show th at these primary intermediates are successively degraded yielding low molec ular weight compounds such as aldehydes, simple organic acids and alpha -ox o-acids, which have been identified by gas chromatography-electron capture detection (GC-ECD), ion chromatography (IC) and GC-MSI respectively. On the basis of the analytical results, a pathway for the degradation of isoprotu ron by ozone has been proposed. (C) 2001 Elsevier Science Ltd. Ali rights r eserved.