Photodegradation and stability of chlorothalonil in water studied by solid-phase disk extraction, followed by gas chromatographic techniques

Photodegradation of chlorothalonil was studied in deionized and ground water with sunlight and Suntest apparatus, with and without FeCl3/H2O2 and TiO2/H2O2. After irradiation of the water samples spiked at 28-100 mu g/l of chlorothalonil, the water solutions were preconcentrated using solid-phase disk extraction with C-18 and analyzed by gas chromatography-electron capture and gas chromatography-mass spectrometric detection. The degradation products identified by GC-MS were: trichlor-1,3-dicyanobenzene, dichloro-1,3-dicyanobenzene and chloro-1,3-dicyanobenzene. The degradation kinetics followed a first order reaction and the R.S.D. of rate constants, for n=3, varied from 2 to 14%. Halflives varied between 0.7 and 101 h. The stability of chlorothalonil on C-18 Empore disks was also investigated at 20 degrees C, 4 degrees C and -20 degrees C for periods of up to 3 months. Chorothalonil was not degraded on C-18 Empore disks. (C) 1998 Elsevier Science B.V. All rights reserved.