Analytical method optimization for study of difenoconazole degradation in substrate with addiction of treated activated domestic sewage sludge

Abstract

Pesticide degradation in soils can be evaluated as a possible solution to minimize the effects of toxic action using recalcitrant compounds on cultivated food and the environment in which it occurs. A common and sustainable alternative is the use of treated sewage activated domestic sludge (TSS) as an adjuvant in soils. The objective of this work was to evaluate the influence of TSS on the degradation profile of a pesticide in the soil. Based on the hypothesis that the use of TSS in soils may influence pesticide degradation, a lab-to-field approach was implemented to determine toxic analyte decay using diphenoconazole (DFC), a triazole class fungicide. Two techniques for sample extraction and clean-up were tested and for each technique two solvents were tested. Also chromatographic conditions were optimized by gas chromatography coupled to mass spectrometry (GCMS) for identification of the main ions and quantification of DFC. The experiment was done in four vessels containing: soil only; soil and TSS in the proportion 70/30%, respectively; soil fortified with DFC; and soil and TSS in the proportion 70/30%, respectively, fortified with DFC. For the degradation study, aliquots were removed from the vessels for 21 days after DFC dosing at a concentration of 20 mg.Kg^-1, respecting the established collection frequency. The method considered most efficient for the determination of DFC used dichloromethane under ultrasound extraction and clean up with the dispersive solid phase extraction technique, using alumina as adsorbent. From the analytical results and the construction of the degradation curves of the two vessels containing the analyte, it was observed that on the first day after dosing there was a sharp drop in the concentration of DFC in both vessels, with greater intensity in the soil only substrate. In the following days the substrate with soil and TSS presented higher decay of DFC in relation to the substrate with soil, confirming significant variation between substrates.