# Ecotoxicological Evaluation of Methiocarb Electrochemical Oxidation
## 1 Introduction  
Emerging contaminants including some pharmaceuticals, personal care products and pesticides are a cause of concern due to their ubiquity in the aquatic environment and their potential for causing deleterious ecological effects [1; 2; 3; 4]. This has led the European Union to establish a surveillance mechanism for the monitoring of substances that show a possible risk to the environment. In 2018, the Commission Implementing Decision (EU) 2018/840 was published, establishing a watch list of substances for Union-wide monitoring in the field of water policy, which includes hormones, antibiotics and pesticides [5]. One of the priority substances identified by the Commission Implementing Decision (EU) 2018/840 watch list is methiocarb (MC), C\({}_{11}\)H\({}_{15}\)NO\({}_{2}\)S, a carbamate pesticide employed in agriculture worldwide, which has been detected in natural waters and in wastewaters [5; 6; 7; 8; 9]. Due to MC and some of its metabolites' high toxicity, the World Health Organization classified MC as a highly hazardous pesticide, being also strictly regulated by the European Union [10; 11; 12]. Although the presence of methiocarb in waters and wastewaters at concentrations ranging from mg L\({}^{-1}\) to \(\upmu\)g L\({}^{-1}\) is usually associated with its use, the industrial production of pesticides and herbicides generates a large volume of wastewaters with a high concentration of these pollutants that, if not properly treated, will also contaminate the water bodies [13; 14]. According to the literature, conventional wastewater treatments are uncapable of removing pollutants such as MC [6; 11]. Thus, new treatment technologies have been studied to achieve the complete degradation of these contaminants to environmentally benign, non-toxic and biodegradable products and prevent their discharge in the aquatic environment [15; 16; 17; 18; 19]. Methiocarb oxidation through CIO\({}_{2}\), NaOCl and NH\({}_{2}\)Cl has been studied by [PERSON] et al. [20] and [PERSON] et al. [21; 22]. The authors found that, despite the effective elimination of MC, a significant increase in toxicity due to the formation of more toxic degradation products occurred. By applying a vacuum ultraviolet/ultraviolet (VUV/UV) process in the degradation of several pesticides including MC, [PERSON] et al. [23] observed a reduction in the toxicity of the solutions although the pesticides' mineralization rates were considerably lower than their degradation rates. [PERSON] et al. [11] studied the removal of MC by ozonation and observed that during the degradation experiments, direct ozone reaction was effective to remove MC but not its formed intermediates whereas hydroxyl radicals could oxidize all species. In fact, treatment technologies based on oxidation through hydroxyl radicals have been widely studied because hydroxyl radicals are one of the most powerful oxidizing species that are able to react unselectively and instantaneously with the surrounding organic pollutants [24]. Among these technologies, electrochemical processes have received great attention due to their versatility, ease in operation and, specially, their high efficiency in the degradation of recalcitrant compounds [17; 25]. Several authors have reported the removal of pesticides and herbicides using different electrochemical methods including electrochemical oxidation (EO), electro-Fenton (EF), photoelectron-Fenton (PEF) and electrochemical peroxidation [13; 14; 26; 27; 28]. In the degradation of solutions containing 100 mg L\({}^{-1}\) of the herbicide clopyralid, [PERSON] et al. [14] found that, among EO with electrogenerated hydrogen peroxide, EF and PEF processes, PEF led to the most attractive results with almost a complete transformation of clopyralid in inorganic ions. In a different study, [PERSON] et al. [26] applied an EO process utilizing dimensionally stable anodes (DSA) to degrade the insecticide imidacloprid at a concentration of approximately 25 mg L\({}^{-1}\) and achieved its complete oxidation (100% mineralization).