Investigations of the behavior of the herbicide bentazon in soil

Bentazon has been used worldwide for broad leaf weeds control in paddy fields and leguminous crops; normally it is applied as post-emergence treatment. A gaschromatographic method was developed to determine the residues of this herbicide in soil. After a series of extraction (water, ethyl-acetate), the soil extracts were concentrated and treated with diazomethane in methanol, which forms the termally stable methyl-bentazon. Residues were screened by GC with flame ionization detector. Detection limit was 0.5 ppm and, at 10 ppm in soil, the recovery was 95.5%. Besides the long-term fate of bentazon in soil has been investigated. The experiment was conducted in pot, under laboratory conditions (25 degrees C, 50% maximum moisture capacity, darkness), the herbicide treatments were at the field rate (10 ppm) and 10 fold, the total incubation time was 30 weeks. The data obtained at our conditions indicate an approximate half life of 4 weeks. After 30-week incubation, at the highest rate, the 34% of the herbicide applied was recovered.