# Ecotoxicological Evaluation of Methiocarb Electrochemical Oxidation
## 1 Introduction
According to these authors, the imidacloprid degradation occurred via direct anodic oxidation and Cl\({}_{2}\)-mediated oxidation and the breakdown of the insecticide's molecular structure and formation of short chain compounds occurred before its complete mineralization. In a study performed by [PERSON] et al. [28], the performance of different anode materials, Pb/PbO\({}_{2}\), Ti/SnO\({}_{2}\) and a boron-doped diamond anode (BDD), was evaluated during the electrochemical oxidation of the pesticide methamidophos at a concentration of 50 mg L\({}^{-1}\). A few authors have found that, using Pb/PbO\({}_{2}\) and Ti/SnO\({}_{2}\), formaldehyde appeared as a product of the reaction, giving evidence of an indirect mineralization mechanism. However, when BDD was used, formaldehyde production was not detected and the formation of phosphate was observed instead, indicating the complete mineralization of methamidophos. In fact, EO using a BDD anode has been regarded as the electrochemical process of choice with outstanding degradation results that are due to the higher oxidation ability of BDD compared with other anode materials [29; 30; 31; 32; 33]. Although the application of the EO process in the treatment of waters and wastewaters appears as an attractive alternative for the degradation of biorefractory or priority pollutants such as pesticides and herbicides, the influence of the EO treatment in the toxicity of the treated solutions is not well known because the removal of the contaminants might not always correspond to a quantitative reduction of the toxic effects. The physicochemical and biological parameters usually determined to evaluate the quality of wastewaters are not sufficient to assess the toxicity to organisms where ecotoxicological tests with aquatic organisms are required to better characterize the toxicity removal and prevent undesirable ecological effects in the aquatic environment caused by wastewater discharge [34]. Hence, the present work aims to fill this gap by evaluating the ecotoxicity of methiocarb solutions treated by EO using the freshwater crustacean _Daphnia magma_ as the model species, as endorsed by international organizations including the American Society for Testing and Materials (ASTM, USA), the Organization for Economic Cooperation and Development (OECD, France) and the International Organization for Standardization (ISO, Switzerland). In the particular case of the highly toxic pesticide methiocarb, there are no studies addressing its degradation by electrochemical oxidation with a subsequential ecotoxicological evaluation. Thus, electrochemical oxidation experiments utilizing a BDD anode were performed with MC aqueous solutions at a concentration of 20 mg L\({}^{-1}\). In order to assess the influence in the toxicity results of two major experimental conditions that greatly affect the EO performance, MC degradation was carried out at two different applied current densities (_j_), 100 and 300 A m\({}^{-2}\), utilizing two different supporting electrolytes, NaCl and Na\({}_{2}\)SO\({}_{4}\). Although the MC concentrations reported for waters and wastewaters are in the range of ng L\({}^{-1}\) to \(\upmu\)g L\({}^{-1}\), the concentration of 20 mg L\({}^{-1}\) was selected for this study with the aim of evaluating the ability of the EO process to reduce the high toxicity of this priority substance in an extreme-case scenario and attending to the concentrations found in the literature for electrochemical studies involving pesticides and herbicides. In addition, in the cases where membrane filtration processes are utilized to purify the effluents, the concentrations in the permeate may reach values much higher than those usually found at the entrance of the effluent treatment plants.