A novel estrogenic compound transformed from fenthion under UV-A irradiation.

The photo-transformed products of fenthion well-known as one of the most photosensitive organophosphorus insecticides and their estrogenic activities were investigated using a yeast two-hybrid assay incorporating the human estrogen receptor alpha (hERalpha). We identified fenthion sulfoxide and 3-methyl-4-methylsulfinylphenol (MMS) as the major transformed products and 3-methyl-4-(methylthio)phenol (MMP) as the minor product under UV-A irradiation. Further, significant estrogenic activity was observed in the solution irradiated for 160 min; this activity was evaluated as 18 pM converted to 17beta-estradiol (E(2)) equivalent concentration. By using authentic standards, it was found that MMP possessed weak estrogenic activity; its activity was evaluated as 1.7x10(-6) times compared with that of E(2). However, it was also revealed that the activity due to MMP was only 13%. From high-performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR) spectroscopies, we newly identified a significant estrogenic compound transformed from fenthion, O,O-dimethyl S-[3-methyl-4-(methylthio)phenyl]phosphorothioate, S-aryl fenthion.

New insights into the photoreactivity of the organophosphorus pesticide fenthion: a sigma aryl cation as a key intermediate in the photodecomposition.

The primary photodegradation processes of fenthion (FN), one of the most photosensitive pesticides used in agriculture, have been investigated by combining laser flash photolysis and steady-state measurements. The triplet state of FN is produced quite efficiently (Phi(isc) approximately 0.3). However, this excited state does not seem to trigger the primary photodecomposition pathways of the pesticide. It is demonstrated that FN undergoes photoheterolysis via the excited singlet state and gives the corresponding singlet "sigma aryl cation". Chemical evidence for the generation of this transient species is given by trapping with typical "sigma nucleophiles" such as chloride and methanol. This photodegradation mechanism is, in part, quite different with respect to what is known to date and may account for the formation of the O,O-dimethyl S-[3-methyl-4-(methylthio)phenyl] phosphorothioate discovered as a novel photodegradation product of FN.

Photolysis of pesticides: influence of epicuticular waxes from Persica laevis DC on the photodegradation in the solid phase of aminocarb, methiocarb and fenthion.

Pesticides with N,N-dimethyl and thiomethyl moieties (aminocarb, methiocarb and fenthion) were irradiated under artificial light (lambda > 290 nm) in an amorphous wax phase from Persica laevis DC. The effect of the presence of the wax on the photolysis rate differed in the three pesticides, increasing it in aminocarb, having little effect in methiocarb and slowing it down in fenthion. The presence of the wax affected the qualitative photodegradation behaviour of all the pesticides. The data obtained were compared with those for pirimicarb, which had been studied earlier.