Distribution and decomposition dynamics of atrazine in an Ultisol under wet tropical climate conditions

The biodegradability and distribution of pesticides in the environment determine their pollution potential. The risk of contamination with atrazine herbicide was studied in an Ultisol under field conditions and complemented with a microcosm system study. This system allowed the use of C-14-atrazine under controlled conditions and to determine of the volatilization (0.33%), mineralization (0.25%) and leaching (4 to 11%) parameters, which are difficult to evaluate in the field. Ninety percent of the radioactivity remained in the soil, with 75% in the first 5 cm. The field experiment was carried out during the dry season, allowing the simulation of summer rains. Results showed that 90 days after the application, atrazine was found at a depth of 50 cm and could well have reached the groundwater. Atrazine lost by runoff was found mainly in the liquid phase (1.6% of total applied), whereas 0.4% was adsorbed to the eroded particles. The atrazine concentration in the runoff was higher on the second day after application, decreasing to less than a tenth of that value after 15 days. These results suggest that application of this herbicide needs to be avoided when rain is forecast due to the pollution potential for ground and surface water in this hind of soil.