UNEQUIVOCAL IDENTIFICATION OF COMPOUNDS FORMED IN THE PHOTODEGRADATION OF FENITROTHION IN WATER-METHANOL AND PROPOSAL OF SELECTED TRANSFORMATION PATHWAYS

The photodegradation of fenitrothion was examined in a mixture of dist illed water/methanol (5:1), The UV irradiation was carried out with a high-pressure Hg lamp during 7 h. For the identification of further br eakdown products, fenitrooxon and carboxyfenitrothion were also irradi ated under experimental conditions identical to those for fenitrothion . The identification of the breakdown products formed was carried out by gas chromatography-mass spectrometry (GC-MS) with electron impact ( EI) and comparison with authentic standards synthesized in the laborat ory. A total of 21 photoproducts of oxidation, isomerization, denitrat ion, and solvolysis that may be of concern in environmental studies we re unequivocally identified. Among them were formyldenitrofenitrothion , carbomethoxydenitro-fenitrooxon, and hydroxymethyldenitrofenitrooxon . A proposed mechanism of the process is presented. Selected pathways for the photodegradation of fenitrothion were examined: (i) degradatio n through hydrolysis, with eventual remethylation; (ii) P=S to P=O oxi dation; (iii) denitration; and (iv) oxidation of the methyl substituen t through hydroxymethyl and formyl to give the corresponding carboxy d erivatives.