RAPID DEGRADATION OF FENITROTHION IN ESTUARINE WATERS

The degradation of fenitrothion under real environmental conditions was studied. Fenitrothion was applied in the irrigation ditches of the Ebre Delta (Tarragona, Catalonia) at an estimated concentration of 200 (situation 1) and 20 mug/L (situation 2) in order to eliminate the american crab (Procamburus clarkii). The evolution of the levels of fenitrothion and the formation of transformation products (TPs) were recorded during the 4 days after application. The TPs formed were 3-methyl-4-nitrophenol, fenitrooxon, and S-methyl isomer of fenitrothion. The concentration of fenitrothion decayed sharply in 2 h with 6% and 0.3% of the initial concentrations in situations 1 and 2, respectively, and reached a steady state within 10 h with a concentration of 4 and 0.01 mug/L, respectively, which was constant for the 4 days the experiment lasted. TPs were encountered at a very low concentration, around 0.01 mug/L. For the identification of fenitrothion and its TPs, solid-phase extraction with C18 Empore extraction disks followed by GC-MS with EI and NCI was used. Good sensitivity was obtained with both techniques, and qualitative information on the fragment ions of all the pesticides detected is given. Half-life of fenitrothion was of 13 h, with a disappearance rate of 0.053 and photolysis being the main pathway. In addition, the degradation of fenitrothion and the formation of TPs are closely related to the environmental conditions; in our experiment, a quick decay of the concentration of fenitrothion could be enhanced by the strong wind that usually affects the treated area.