The sterilization methods are particularly important to study the influence of microorganisms on the pesticide dissipation in soils. This study, conducted in the laboratories of the Instituto Biológico of São Paulo in august 1996, tested the influence of two methods of soil sterilization - moist heat (autoclaving) and γ radiation - on the release of nonextractable or bound residues. It was studied, as example, bound residues of the herbicide atrazine in two types of soil (gley humic and dark red latosol). In the soil samples submitted to the moist heat sterilization, the recovery of the previously bound residues as reextractable residues was 5.6 and 5.9 times higher than in the control soils, not submitted to any sterilization process. Therefore, the method itself released the residues, indicating that the autoclaving is not the most appropriate method for studies on the influence of microorganisms on the release of bound residues. Otherwise, the γ radiation did not modify the residues recovery when compared to the controls.
microorganisms; dissipation; 14C-bound residues