Insights on the removal of the azole pesticides included in the EU Watch List by Catalytic Wet Peroxide Oxidation

The aim of this work is to evaluate the feasibility of the Catalytic Wet Peroxide Oxidation (CWPO) process using the inexpensive and environmentally friendly Fe3O4-R400 catalyst for the removal from water of a representative group of azole pesticides recently listed in the European Union (EU) Watch Lists (penconazole (PEN), prochloraz (PCZ), tebuconazole (TEB), tetraconazole (TET), metconazole (MET)). The complete removal of these pollutants (1000 μg L−1) was achieved in <1 h reaction time under ambient conditions using a catalyst concentration of 0.5 g L−1 and the stoichiometric dose of H2O2 (3 – 5 mg L−1) at a slightly acidic pH (pH0 = 5.0). To further demonstrate the effectiveness of the process, the ecotoxicity abatement was also considered. The initial toxicity of the pesticides and the CWPO effluents were evaluated with the brine shrimp Artemia salina and the bacterium Vibrio fischeri. Remarkably, the effluents were non-toxic for V. fischeri and a decrease of more than 80% in mortality was achieved for A. salina. Furthermore, the versatility of the system was proved in real water matrices (surface water and WWTP effluent), although a slight decrease on the oxidation rate was found due to the occurrence of organic matter and inorganic salts. The reactivity of the azole pesticides was finally compared with the achieved for other groups of pollutants included in the EU Watch Lists (pharmaceuticals, hormones, and neonicotinoid pesticides). Clearly, azole compounds showed the least reactivity to oxidation, suggesting that they can be used as general indicators of the overall efficiency of the proposed catalytic system for the removal of EU Watch Lists micropollutants.