Accelerated Degradation of 14C-Atrazine in Brazilian Soils from Different Regions

The repeated use of a given pesticide may induce a selection of the soil microbial population, resulting in a rapid degradation of the respective xenobiotic. Patterns of atrazine degradation (mineralization, formation of metabolites and nonextractable residues (NER)) were evaluated in two Brazilian soils with a history of atrazine application. Results were compared with those obtained from soils that had no agricultural use or herbicide application history. C-14-Atrazine mineralization in unsaturated treated soils was high. By the 85th day of incubation, 82% of the applied C-14-atrazine was mineralized in the Rhodic Hapludox and 74% in the Xanthic Haplustox. Mineralization remained low in nontreated soils (<= 5.1%). Incubation under slurry conditions enhanced atrazine mineralization in the treated Xantic Haplustox and surprisingly also in the nontreated Rhodic Hapludox (98 and 83% on the 85th day, respectively), whereas in the other samples the evolved (CO2)-C-14 did not differ (p < 0.05) from the unsaturated conditions. The water-extractable amount of atrazine directly after C-14-atrazine application was higher in both Xanthic Haplustox samples (around 80% of applied atrazine) in comparison to the Rhodic Hapludox samples (around 60%). Extractable activity and the formation of metabolites and NER varied among the studied soils according to the atrazine application history rather than the soil characteristics.