Hydrolytic dissipation of four sulfonylurea herbicides

The fate of prosulfuron, primisulfuron methyl, rimsulfuron, and thifensulfuron methyl in aqueous solutions was investigated, using capillary electrophoresis (CE) for herbicide detection. The hydrolysis of the four sulfonylureas followed first-order kinetics and was pH dependent and accelerated at higher temperature. Rimsulfuron and thifensulfuron methyl showed fast degradation in water, with half-lives from 12 to 0.06 days in the pH range from 2 to 8.5 at 25 degrees C. The degradation rate of prosulfuron and primisulfuron methyl resulted relatively slow, with half-lives from 49 to 399 days in the pH range from 5 to 7.5, at 25 degrees C. The hydrolysis of the four sulfonylureas as a function of temperature and pH was mathematically combined. The resulting complex equations represent simple and useful models to predict the hydrolytic dissipation of these sulfonylureas. The complex equations of prosulfuron and primisulfuron methyl suggest that once these herbicides reach the groundwater, they would tend to persist, due to their slow degradation at neutral and subalkaline pi-Is and low temperatures, On the contrary, rimsulfuron and thifensulfuron methyl would not create problems of aquifer pollution, due to their fast hydrolysis in a wide range of pH and temperature combinations.