# Ecotoxicological Evaluation of Methiocarb Electrochemical Oxidation
## 3 Results and Discussion
The possible formation of organochlorinated compounds  
Figure 3: (**a**) EC\({}_{50}\) results obtained for the treated solutions at 100 and 300 A m\({}^{-2}\) using Na\({}_{2}\)SO\({}_{4}\) or NaCl as the supporting electrolyte. (**b**) Comparison of the toxicity of the different methiocarb solutions in terms of toxic units before and after treatment at the different experimental conditions. in the last hour of the assay, although in low concentration because the TOC was less than 1 mg L\({}^{-1}\) at this point, could also be a possible explanation for the increased ecotoxicity. Both perchlorate and organochlorinated compound formation can also explain the lower ecotoxicity reduction presented by the chloride-containing solutions treated at 300 A m\({}^{-2}\). At the applied charge of 3.24 kC (3 h assay at 300 A m\({}^{-2}\)), EC\({}_{50}\) increased only to 32%. At higher applied current densities, chloride oxidation and hydroxyl radical formation were enhanced, augmenting the occurrence of the reactions described by Equations (1)-(4) and the possible formation of organochlorinated compounds. For the solutions prepared with sulfate at 100 A m\({}^{-2}\), EC\({}_{50}\) increased from 0.21% to 22% after a 5 h assay (1.8 kC) and to 32% after 6 h (2.16 kC). These results agreed with the lower MC degradation rate observed for the solutions containing sulfate and indicated that at 1.8 kC there were in the solution toxic MC degradation products that were being further oxidized to less or non-toxic compounds, decreasing the solution toxicity at 2.16 kC. Nevertheless, the increase in applied current density and charge did not result in a further decrease in toxicity. At the applied charge of 3.24 kC (3 h assay at 300 A m\({}^{-2}\)), EC\({}_{50}\) increased only to 25% in the sulfate-containing solution. This result can be explained by the energy efficiency loss when \(j\) was increased as observed for the TOC removal, mainly due to mass transport limitations. In terms of toxic units (Figure 3b), it can be seen that, using NaCl as the supporting electrolyte, it was possible to reduce the toxicity more than 200\(\times\) from 370.9 TUs to 1.6 TUs with 5 h treatment at 100 A m\({}^{-2}\), whereas for the same conditions but using Na\({}_{2}\)SO\({}_{4}\), the reduction was only of 107\(\times\) from 470.4 TUs to 4.4 TUs. At the higher applied current density of 300 A m\({}^{-2}\), the difference between the supporting electrolytes was less pronounced, with a similar reduction in toxicity of 120\(\times\) versus 115\(\times\) for NaCl and Na\({}_{2}\)SO\({}_{4}\) containing solutions, respectively. Overall, the results obtained clearly demonstrated the remarkable efficiency of EO treatment for MC complete degradation and its high potential for reducing the toxic ecological effects of this highly hazardous pesticide even when present in concentrations far above those currently reported for waters and wastewaters. According to [PERSON] et al. [35], the MC solutions went from being classified as highly toxic before treatment to toxic and very close to be considered non-toxic after EO treatment. Although the present study only addressed experiments at a laboratory scale, it offers a useful contribution to further develop the application of the electrochemical oxidation process at an industrial level. In fact, according to the results achieved, EO can be considered suitable for the remediation of contaminated industrial or agricultural wastewaters, enabling the elimination of MC and its adverse effects before they reach the aquatic environment.