ANALYSIS AND BEHAVIOR OF ORGANOPHOSPHORUS PESTICIDES IN A RICE CROP FIELD

A comprehensive analytical protocol for the determination of organophosphorus pesticides in the biotic and abiotic compartments of a rice crop field (Ebro delta, Spain) is described. This include two alternative clean-up procedures (Florisil column chromatography and Bio Beads SX-3 gel permeation chromatography) and gas chromatographic analysis with nitrogen-phosphorus and mass spectrometric detection. Among the pesticides identified, Fenitrothion was the most abundant with residue levels in sediment samples varying from 1 - 3-mu-g/g in the first day of application to 0.5-mu-g/g two days after, whereas in the water canals the concentrations were of 3 - 10-mu-g/1, after aircraft application, with a rapid decrease several hours later. Half lives of Fenitrothion in water and sediment samples under natural conditions have been estimated to be lower than 1 day and between 1 - 1.5 days, respectively, with volatilization and microbial degradation accounting for this decay. The bivalves analysed in the coastal bays (Tapes semi-decussatus, Ostrea edulis and Mytilus galloprovincialis) exhibited residue levels between 20 - 90 ng/g of organophosphorus pesticides, Fenitrothion being the most abundant organophosphorus pesticide. These levels are likely in the safe range for bivalves but not for other organisms such as crustacea, which are sensitive to water concentrations of 0.1-mu-g/l.