Advanced treatment of water contaminated with atrazine, difenoconazole and fipronil mixture, its by-products and bio-toxicity levels

The pesticides atrazine (ATZ), difenoconazole (DFN) and fipronil (FPN) are widely used in different crops. These compounds have been detected in water matrices and present toxic potential to aquatic fauna as well as human health, especially when presented as a mixture of pesticides due to their synergistic effects. Therefore, a mixture of these three pesticides, named ADF, was prepared to investigate the efficiency of degradation of each compound and the mineralization of ADF by the application of a photo-electro Fenton (PEF) process with boron-doped diamond (BDD) anode (PEF-BDD). The concentration of ADF was determined by High-Performance Liquid Chromatography (HPLC) analysis. Preliminary tests were performed, enabling the application of a desirability function and a Response Surface Methodology (RSM) to obtain the optimal operating conditions of the electrolytic cell, namely applied electric current (AEC) of 0.7 A, H2O2 concentration of 1000 mg L−1, and flow rate of 0.6 L min−1, within 15 min of PEF-BDD process, reaching a degradation in the mixture of 95.7% ATZ, 97.3% DFN and 96.5% FPN and mineralization of 47.3% of the ADF solution. Bio-toxicity levels displayed by the bioindicators Artemia salina (acute toxicity) and Allium cepa (cytotoxicity) were assessed and, in addition, a study of intermediate reaction by-products identified by Gas Chromatography-Mass Spectrometry (GC-MS) was carried out. Finally, this study aims to provide a comprehensive understanding of the application potential of the PEF-BDD process for efficient treatment of surface and groundwater contaminated with pesticides in a mixture.