# Ecotoxicological Evaluation of Methiocarb Electrochemical Oxidation
## 4 Conclusions  
Electrochemical oxidation with a BDD anode can effectively degrade methiocarb and its transformation by-products, reducing drastically the acute toxicity towards _Daphnia magma_. The MC electrodegradation mechanism depends on the species present in the solution and on the applied current density:  
* In the presence of chloride, MC is rapidly transformed as result of its additional indirect oxidation by active chlorine species. These active chlorine species are responsible for the nitrogen elimination, above 50%.
* In the presence of sulfate, the electrooxidation mechanism involves mainly hydroxyl radicals formed at the BDD surface leading to a slow MC elimination because the oxidation rate depends on the MC diffusion to the anode's surface. No nitrogen removal was observed using this supporting electrolyte.
* An increase in current density enhances secondary reaction rates, thus decreasing the energy efficiency. An exception is nitrogen removal in chloride-containing solutions, which is promoted by the increased amount of active chlorine species.  
* Chloride-containing solutions lead to higher toxicity reductions than sulfate-containing solutions most likely due to the faster MC degradation and of its transformation products when NaCl is used.
* In chloride-containing solutions, the increase in applied electric charge due to the increase in assay duration or applied current density leads to a lower decrease in ecotoxicity probably due to the formation of perchlorate and organochlorinated compounds.  
At optimized experimental conditions, the EO process offers a suitable solution for the treatment and elimination of undesirable ecological effects of MC contaminated industrial or agricultural wastewaters, ensuring that this priority substance is not transferred to the aquatic environment.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/21/7435/s1](http://www.mdpi.com/2076-3417/10/21/7435/s1)]([http://www.mdpi.com/2076-3417/10/21/7435/s1](http://www.mdpi.com/2076-3417/10/21/7435/s1)), Figure S1: Number of immobilized daphnids after 24 and 48h of exposure to the different treatments. Immobilization refers to the inability of animals that are not able to swim within 15 seconds, after gentle agitation of the test vessel [1].  
Conceptualization, A.L.; methodology, A.F. and A.C.S.; validation, A.F. and A.C.S.; investigation, C.P., S.C. and C.F.; resources, M.R.P. and L.C.; writing--original draft preparation, A.F. and A.C.S.; writing--review and editing, M.R.P., M.J.P., L.C. and A.L.; visualization, M.J.P.; supervision, A.L.; project administration, A.F. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Fundacao para a Ciencia e a Tecnologia, FCT, through UID Fiber Materials and Environmental Technologies (FibEnTech), project UIDB/00195/2020. Further financial support was provided by funds from the Health Sciences Research Center (CICS-UBI) through National Funds by FCT (UID/Multi/00709/2019).  
A.C.S. acknowledges University of Aveiro for funding in the scope of the framework contract foreseen in the numbers 4, 5 and 6 of the article 23, of the Decree-Law 57/2016, of August 29, changed by Law 57/2017, of July 19 and project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript or in the decision to publish the results.