Degradation of chlortoluron in water disinfection processes: a kinetic study

The kinetics of the reaction between chlortoluron, a phenylurea herbicide [ N'-(2-hydroxy-4-methyl-5-chlorophenyl)-N,N-dimethylurea], and hypochlorite, the active species in water disinfection processes involving chlorine, wer e investigated by HPLC-UV and HPLC-electrospray ionisation mass spectrometr y (HPLC-ESI-MS). In particular, the concentrations of the main chlortoluron by-products were monitored as a function of time by HPLC-ESI-MS and a kine tic model was developed to fit the relevant curves. The results showed that chlortoluron degradation starts with two parallel pathways, namely, chlori nation and hydroxylation of the aromatic ring, which are then followed by c onsecutive chlorination reactions, and after almost 2 weeks by ring opening and partial mineralisation, as confirmed by head-space solid-phase microex traction gas chromatography-MS (SPME-GC-MS) and total organic carbon (TOC) measurements. Kinetic constants for the first reactions of the overall proc ess, under pseudo-first-order conditions (hypochlorite excess), were estima ted by a fitting procedure.