Reducing toxicity and antimicrobial activity of a pesticide mixture via photo-Fenton in different aqueous matrices using iron complexes

Abstract

This is the first study to investigate ethylenediamine-N,N′-disuccinic acid (EDDS)/photo-Fenton process to polish real wastewater containing pesticides for possible water reuse. To this end, simultaneous degradation of pesticides ametrine, atrazine, imidacloprid and tebuthiuron was evaluated in distilled water (DW) and in sewage treatment plant (STP) effluent at initial pH 6.0. Several operational parameters (Fe3+-EDDS concentration, Fe3+-EDDS molar ratio, EDDS addition patterns and radiation source) were evaluated. 80–98% removal of target pesticides were obtained in DW using 30 μmol L−1 of Fe3+-EDDS with a molar ratio of 1:2 (300 μmol L−1 of H2O2). In addition, the proposed Fe3+-EDDS photo-Fenton at pH 6 was more efficient than classic photo-Fenton at pH 2.7 (30–84% removal). Experiments conducted in the presence of radical trapping agents (2-propanol or chloroform) revealed that HO• was the most active radical during treatment. Matrix composition strongly affected the degradation of target pesticides as a six-fold higher concentration of reagents (180 μmol L−1 of Fe3+-EDDS and 1800 μmol L−1 of H2O2) was needed to reach the same efficiency in STP compared to DW. Even so, first order rate constants corresponding to the degradation of pesticides in DW (k = 0.098–0.85 min−1) were nearly two-fold higher than in STP (k = 0.079–0.49 min−1) under the same radiation source (black-light or solar radiation). Finally, acute toxicity towards Vibrio fischeri and Drosophila melanogaster flies, and antibacterial activity assessed for Escherichia coli were eliminated after the application of the proposed treatment, thus indicating environmental safety for either discharge or reuse of treated wastewater for crop irrigation in agriculture.