DETERMINATION OF THIOBENCARB RESIDUES IN WATER AND SOIL USING SOLID-PHASE EXTRACTION DISKS

The movement and degradation of the herbicide thiobencarb was monitored in a rice field near Lake Albufera (Valencia, Spain). This area constitutes an ecological unit of great environmental interest. Soil samples were collected from the surface and the subsurface of the rice field treated with this herbicide. Soil characterization tests for pH, organic matter, moisture and texture were also carried out. At the same time, samples of water were taken from the inundated plot 10 cm below the surface. Both types of sample were extracted by solid-phase extraction using 47-mm discs of octyl-bonded silica sorbent and eluted with ethyl acetate, with average recoveries for this compound of 63 and 93% from soil and water, respectively. The analyses were carried out by gas chromatography with nitrogen-phosphorus detection. Sample components were separated with a 30 m x 0.25 mm I.D. fused-silica capillary column coated with 50% phenylmethylsilicone (DB-17).