Disappearance of aerially applied fenitrothion in rice crop waters

The disappearance of fenitrothion under real environmental conditions was studied. Fenitrothion was applied in the rice crop field of the Ebre Delta (Tarragona, Spain) during July 1995 by helicopter spraying at a rate of 148 mL/ha Tionfos 50 LE (50% of pure fenitrothion). For monitoring fenitrothion residues in water, two different analytical techniques were used: enzyme-linked immunosorbent assay (ELISA) and automated on-line solid-phase extraction (Prospekt) followed by liquid chromatography/diode array detection (LC/DAD). The unequivocal identification of fenitrothion, fenitrooxon, 3-methyl-4-nitrophenol, and s-methyl isomer of fenitrothion was achieved by liquid chromatography/mass spectrometry (LC/MS) using an atmospheric pressure chemical ionization (APCI) interface in the negative ionization (Nl)mode. The residue levels of fenitrothion in rice crop field waters varied from 119-178 mu g/L down to 3.8-1.5 mu g/L after 48 h of helicopter application. The half-lifetimes t(1/2) were calculated by both analytical techniques being 19.3 for ELISA and 11 h for LC/DAD after treatment, with a disappearance rate of 0.036 and 0.063, respectively.