Optimal degradation of organophosphorus pesticide at low levels in water using fenton and photo-fenton processes and identification of by-products by GC-MS/MS.

Abstract

This study aiming to determine the optimal conditions to degrade an organophosphate pesticide diazinon (DZN) at low levels concentrations (μg.mL-1) and to identify the by-products generated. The degradation processes utilized were the Fenton and photo-Fenton. The iron concentration [Fe2+], the hydrogen peroxide concentrations [H2O2], and the solution pH are the investigated parameters. The Doehlert three-parameter experimental design was applied to model and optimize both degradation processes. The mathematical models suggested were assessed and validated by application of analysis of variances ANOVA. In the case of Fenton process, the greatest yield of degradation (79%) was obtained at [Fe2+] = 35 mg.L-1 (0.63 mmol.L-1), [H2O2] = 423 mg.L-1 (12.44 mmol.L-1), and pH = 5.0. In photo-Fenton process, the maximum yield of degradation (96%) was obtained under the conditions of [Fe2+] = 29 mg.L-1 (0.52 mmol.L-1), [H2O2] = 258 mg.L-1 (7.59 mmol.L-1) and pH = 4.6. QuEChERS (quick, easy, cheap, effective, rugged, and safe), as extraction technique, and GC-MS/MS (gas chromatography coupled with triple quadrupole mass spectrometry) were used to identify the by-products degradation of DZN. The identified compounds are diazoxon, triethyl phosphate, triethyl thiophosphate, 2-isopropyl-5-ethyl-6-methylpyrimidine-4-ol, 2-isopropyl-6-methylpyrimidine-4-ol (IMP) and hydroxydiazinon. Three possible pathways for diazinon degradation have been suggested and the hydroxylation, oxidation and hydrolysis are likely probable degradation mechanisms.