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 sol vent extraction, thin-layer chromatography and radiometric techniques. Results here presented show it was directly proportional to the tempe rature increases. As the temperature increased, less extractable and m ore bound residues were detected. At the end of the incubation period, soil extracts contained mainly atrazine but also its hydroxyderivativ e at 10 degrees C and 20 degrees C, and more hydroxyatrazine than atra zine at 30 degrees C and 40 degrees C. The calculated Arrhenius activa tion energy was very high (96 kJ . mol(-1)) proving the predominance o f 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 wit h the characteristics of the soil here studied and at temperatures hig her than 20 degrees C, atrazine would not be a free contaminant becaus e chemical degradation would result only in the non-phytotoxic hydroxy atrazine, either as available or as bound residues.