Atrazine, an herbicide of the s-triazine group, was used in laboratory experiments to determine its mineralization and sorption on samples of a Dusky-Red Latosol under conventional and no-tillage systems. Atrazine ring-labeled 14C was added to the soil samples, with the 14CO2 being produced and atrazine-14C soil extracts analyzed by liquid scintillation. The results showed very low mineralization rates of atrazine, which were correlated with the total carbon and nitrogen contents, as well as with soil humic fractions. Atrazine mineralization decreased with depth, whereas the soil under no-tillage system showed higher atrazine mineralization compared with the conventional system, due to higher amounts of organic matter in the former. On the other hand, the lag phase of the conventional system was shorter, indicating a greater adaptation of the microbial community to degrade atrazine in soils where application of this herbicide is a common pre-emergence practice. The addition of organic substrates resulted in increasing atrazine mineralization. It was also verified that atrazine had a short-term sorption component of two hours, followed by a slower component established up to 12 hours. The soil organic matter was the main factor controlling atrazine sorption (50% of added atrazine), whereas iron/aluminum oxides and 1:1 clay minerals had no significant contribution to the sorption process (about 5% of the added atrazine). Soils with low organic matter content are not able to absorb enough atrazine to avoid subsurface contamination, resulting in serious risks of watertable pollution.
biodegradation; adsorption; Oxisols; herbicide