Evaluation of amicarbazone toxicity removal through degradation processes based on hydroxyl and sulfate radicals

The herbicide amicarbazone (AMZ), which appeared as a possible alternative to atrazine, presents moderate environmental persistence and is unlikely to be removed by conventional water treatment techniques. Advanced oxidation processes (AOPs) driven by ^•OH and/or SO₄^•- radicals are then promising alternatives to AMZ-contaminated waters remediation, even though, in some cases, they can originate more toxic degradation products than the parent-compound. Therefore, assessing treated solutions toxicity prior to disposal is of extreme importance. In this study, the toxicity of AMZ solutions, before and after treatment with different ^•OH-driven and SO₄^•--driven AOPs, was evaluated for five different microorganisms: Vibrio fischeri, Chlorella vulgaris, Tetrahymena thermophila, Escherichia coli, and Bacillus subtilis. In general, the toxic response of AMZ was greatly affected by the addition of reactants, especially when persulfate (PS) and/or Fe(III)-carboxylate complexes were added. The modifications of this response after treatment were correlated with AMZ intermediates, which were identified by mass spectrometry. Thus, low molecular weight by-products, resulting from fast degradation kinetics, were associated with increased toxicity to bacteria and trophic effects to microalgae. These observations were compared with toxicological predictions given by a Structure-Activity Relationships software, which revealed to be fairly compatible with our empirical findings.