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 Eb re Delta (Tarragona, Spain) during July 1995 by helicopter spraying at a rate of 148 mL/ha Tionfos 50 LE (50% of pure fenitrothion). For mon itoring fenitrothion residues in water, two different analytical techn iques were used: enzyme-linked immunosorbent assay (ELISA) and automat ed on-line solid-phase extraction (Prospekt) followed by liquid chroma tography/diode array detection (LC/DAD). The unequivocal identificatio n of fenitrothion, fenitrooxon, 3-methyl-4-nitrophenol, and s-methyl i somer of fenitrothion was achieved by liquid chromatography/mass spect rometry (LC/MS) using an atmospheric pressure chemical ionization (APC I) interface in the negative ionization (Nl)mode. The residue levels o f fenitrothion in rice crop field waters varied from 119-178 mu g/L do wn to 3.8-1.5 mu g/L after 48 h of helicopter application. The half-li fetimes 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.