Effect of temperature on dissipation of [C-14]-atrazine in a Brazilian soil

The soil dissipation of the herbicide C-14-atrazine was studied by solvent extraction, thin-layer chromatography and radiometric techniques. Results here presented show it was directly proportional to the temperature increases. As the temperature increased, less extractable and more bound residues were detected. At the end of the incubation period, soil extracts contained mainly atrazine but also its hydroxyderivative at 10 degrees C and 20 degrees C, and more hydroxyatrazine than atrazine at 30 degrees C and 40 degrees C. The calculated Arrhenius activation energy was very high (96 kJ . mol(-1)) proving the predominance of chemical reactions favouring the hydrolysis. Exploratory analysis of the soil bound residues detected more than 90% as hydroxyatrazine, in all different temperature samples. Results suggest that in a soil with the characteristics of the soil here studied and at temperatures higher than 20 degrees C, atrazine would not be a free contaminant because chemical degradation would result only in the non-phytotoxic hydroxyatrazine, either as available or as bound residues.