processes Article Assessment of Advanced Oxidation Processes Using Zebrafish in a Non-Forced Exposure System: A Proof of Concept Tamia Cabascango 1,2,† , Karol Ortiz 1,2,† , Christian Sandoval Pauker 3 , Isabel Espinoza Pavón 1 , Anuradha Ramoji 4,5 , Jürgen Popp 4,5 , Jady Pérez 1 , C. Miguel Pinto 6 , José Luis Rivera-Parra 7 , Florinella Muñoz-Bisesti 1 , María Belén Aldás 2 , Cristiano V. M. Araújo 8 and Paul Vargas Jentzsch 1, *   Citation: Cabascango, T.; Ortiz, K.; Sandoval Pauker, C.; Espinoza Pavón, I.; Ramoji, A.; Popp, J.; Pérez, J.; Pinto, C.M.; Rivera-Parra, J.L.; Muñoz-Bisesti, F.; et al. Assessment of Advanced Oxidation Processes Using Zebrafish in a Non-Forced Exposure System: A Proof of Concept. Processes 2021, 9, 734. https://doi.org/10.3390/ pr9050734 Academic Editor: Chunjiang An Received: 16 March 2021 Accepted: 19 April 2021 Published: 22 April 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Departamento de Ciencias Nucleares, Facultad de Ingeniería Química y Agroindustria, Escuela Politécnica Nacional, Ladrón de Guevara E11-253, 170525 Quito, Ecuador; tamia.cabascango12@gmail.com (T.C.); karol.ortiz.leon@gmail.com (K.O.); isabel.espinoza@epn.edu.ec (I.E.P.); jady.perez@epn.edu.ec (J.P.); florinella.munoz@epn.edu.ec (F.M.-B.) 2 Departamento de Ingeniería Civil y Ambiental, Facultad de Ingeniería Civil y Ambiental, Escuela Politécnica Nacional, Ladrón de Guevara E11-253, 170525 Quito, Ecuador; maria.aldas@epn.edu.ec 3 Laboratorio de Fisicoquímica, Departamento de Química, Universidad Técnica Federico Santa María, Avenida España 1680, 2390123 Valparaíso, Chile; christian.sandovalp@sansano.usm.cl 4 Institut für Physikalische Chemie and Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Helmholtzweg 4, 07743 Jena, Germany; anuradha.ramoji@uni-jena.de (A.R.); juergen.popp@uni-jena.de (J.P.) 5 Leibniz Institute of Photonic Technology, Albert-Einstein-Straße 9, 07745 Jena, Germany 6 Observatorio de Biodiversidad, Ambiente y Salud (OBBAS), 170525 Quito, Ecuador; pinto@obbas.org 7 Departamento de Petróleos, Facultad de Geología y Petróleos, Escuela Politécnica Nacional, Ladrón de Guevara E11-253, 170525 Quito, Ecuador; jose.riverap@epn.edu.ec 8 Department of Ecology and Coastal Management, Institute of Marine Sciences of Andalusia (CSIC), Puerto Real, 11519 Cádiz, Spain; cristiano.araujo@icman.csic.es * Correspondence: paul.vargas@epn.edu.ec; Tel.: +593-2-2976300 (ext. 4231) † These authors contributed equally to this work. Abstract: Water bodies and aquatic ecosystems are threatened by discharges of industrial waters. Ecotoxicological effects of components occurring in untreated and treated wastewaters are often not considered. The use of a linear, multi-compartmented, non-forced, static system constructed with PET bottles is proposed for the quality assessment of treated waters, to deal with such limitations. Two synthetic waters, one simulating wastewater from the textile industry and the other one simulating wastewater from the cassava starch industry, were prepared and treated by homogeneous Fenton process and heterogeneous photocatalysis, respectively. Untreated and treated synthetic waters and their dilutions were placed into compartments of the non-forced exposure system, in which zebrafish (Danio rerio), the indicator organism, could select the environment of its preference. Basic physical– chemical and chemical parameters of untreated and treated synthetic waters were measured. The preference and avoidance responses allowed verification of whether or not the quality of the water was improved due to the treatment. The results of these assays can be a complement to conventional parameters of water quality. Keywords: ecotoxicological assays; heterogeneous photocatalysis; Fenton; advanced oxidation processes; graphitic carbon nitride; Danio rerio 1. Introduction The human population is growing every year and the obvious consequence is the rise in the global demand for food and goods, which leads to increasing pressure on water sources [1]. Overexploitation of water bodies is the consequence of both the increasing demand for freshwater for different purposes and climate change (droughts are increasing in many regions). According to Mekonnen and Hoekstra [2], approximately 4.0 billion people are under conditions of severe water scarcity for at least 1 month per year; it is reasonable to assume that water scarcity could affect more people in subsequent years as Processes 2021, 9, 734. https://doi.org/10.3390/pr9050734 https://www.mdpi.com/journal/processes