By-products formation during degradation of isoproturon in aqueous solution. II: Chlorination

After a previous study in which the considered oxidant was ozone (Part I), a laboratory investigation has been carried out to study the degradation of the herbicide isoproturon during its reaction with another oxidant. i.e, c hlorine, in aqueous solution (Part II; this paper). The specific aim was to identify the by-products formed. The effects of pH and the presence of bro mide ions were studied. Reactions have been carried out at room temperature , in phosphate buffered aqueous solutions, at four pHs (6, 7, 8 and 9), By- products identification was first performed using relatively high initial r eagent concentrations which were analytically convenient ([isoproturon] = 4 0 mg/l, [HClO + ClO-] = 160 mg Cl/l, [Br-] = 80 mg/l). In follow-up studies , the by-products identified during this preliminary step were searched for when using concentration values closer to those actually encountered at re al water treatment plants ([isoproturon] = 0.4 and 0.004 mg/l, [HClO + ClO- ] = 1.6 mg Cl/l, [Br-] = 0.8 and 0.008 mg/l). Under all of the studied cond itions, the results showed that isoproturon is completely degraded and that it decays much faster in the presence of bromide. The pH has a negligible influence when bromide ions are absent. On the contrary, if bromide ions ar e present, the isoproturon decay is slower at higher pH values. High perfor mance liquid chromatography-mass spectrometry (HPLC-MS) analyses have led t o the identification of several by-products as a result of simultaneous oxi dation and substitution reactions, both occurring on the aromatic ring of t he herbicide. However, the more abundant by-products are those resulting fr om the oxidation of the isoproturon aromatic ring. As far as halogenated by -products are concerned, the higher the bromide ion concentration the highe r the ratio of brominated to chlorinated by-products. On the basis of the a nalytical results, a pathway for isoproturon degradation under the studied conditions is proposed, (C) 2001 Elsevier Science Ltd. All rights reserved.