PHOTODEGRADATION OF THE ORGANOPHOSPHORUS PESTICIDES CHLORPYRIFOS, FENAMIPHOS AND VAMIDOTHION IN WATER

The photodegradation of the pesticides chlorpyrifos, fenamiphos and vamidothion in water containing 2-4% methanol was examined. Acetone (5%) was added as photosensitizer in the photolysis of vamidothion. A suntest apparatus equipped with a xenon arc lamp which exhibits a radiation very close to natural sunlight was employed. Analyses were performed by direct injection of the water samples containing the photoproducts into a liquid chromatograph with diode array and thermospray mass spectrometric detection. The major photodegradation products were identified by matching their diode-array spectra with the corresponding spectra of the authentic standards, their retention times and the spectra obtained using positive and/or negative thermospray mass spectrometry. 3,5,6-trichloro-2-pyridinol, fenamiphos sulfoxide and vamidothion sulfoxide were the major photodegradation products from chlorpyrifos, fenamiphos and vamidothion, respectively.