Plants 2021, 10, 2118. https://doi.org/10.3390/plants10102118 www.mdpi.com/journal/plants Article Interaction Effect of EDTA, Salinity, and Oxide Nanoparticles on Alga Chlamydomonas reinhardtii and Chlamydomonas euryale Emilie Canuel 1 , Cleiton Vaz 2 , William Gerson Matias 3 and David Dewez 1, * 1 Laboratory of Environmental & Analytical Biochemistry of Contaminants, Department of Chemistry, University of Quebec at Montreal, CP 8888, Succ. Centre‐Ville, Montréal, QC H3C 3P8, Canada; emilie.canuel1@gmail.com 2 Centro Universitário—Católica de Santa Catarina, Rua Visconde de Taunay, 427, Joinville CEP‐89203‐005, SC, Brazil; contato.cleitonvaz@gmail.com 3 Laboratório de Toxicologia Ambiental—LABTOX, Departamento de Engenharia Sanitária e Ambiental, Campus Universitário, Universidade Federal de Santa Catarina, Florianópolis CEP 88040‐970, SC, Brazil; william.g.matias@ufsc.br * Correspondence: dewez.david@uqam.ca; Tel.: +1‐514‐987‐3000 (ext. 3278) Abstract: The interaction effects of organic ligand ethylene diamine tetra‐acetic acid (EDTA) and oxide nanoparticles (magnetite Fe3O4‐NPs and copper CuO‐NPs) were investigated during a 72 h period on two green algal species—Chlamydomonas reinhardtii under freshwater conditions and Chla‐ mydomonas euryale under saltwater conditions. Fe3O4‐NPs had larger agglomerates and very low solubility. CuO‐NPs, having smaller agglomerates and higher solubility, were more toxic than Fe3O4‐NPs in freshwater conditions for similar mass‐based concentrations, especially at 72 h under 100 mg L −1 . Furthermore, the effect of EDTA increased nanoparticle solubility, and the salinity caused a decrease in their solubility. Our results on C. euryale showed that the increase in salinity to 32 g L −1 caused the formation of larger nanoparticle agglomerates, leading to a decrease in the tox‐ icity impact on algal cells. In addition, EDTA treatments induced a toxicity effect on both freshwater and saltwater Chlamydomonas species, by altering the nutrient uptake of algal cells. However, C. euryale was more resistant to EDTA toxicity than C. reinhardtii. Moreover, nanoparticle treatments caused a reduction in EDTA toxicity, especially for CuO‐NPs. Therefore, the toxicity impact caused by these environmental factors should be considered in risk assessment for metallic nanoparticles. Keywords: EDTA; Salinity; Fe3O4; CuO; nanoparticles; C. reinhardtii; C. euryale 1. Introduction Nanomaterials are widely used in industries for many technological applications. Nanoparticles of magnetite (Fe3O4‐NPs) are applied in magnetic resonance imaging and medical treatments, such as cancer [1] and in wastewater treatment [2–4]. Nanoparticles of copper oxide (CuO‐NPs) are in fabrics and electronic products, providing antimicrobial and thermal conductivity properties [5,6]. In the long‐term, massive production of these nanomaterials may represent a risk of contamination for aquatic environments, from their manufacturing into consumer products to their utilization and degradation [7]. It was previously suggested that the toxicity mechanisms of metallic NPs were de‐ pendent on their physicochemical properties [8–11]. Several studies investigated the tox‐ icity effects of Fe3O4‐NPs and CuO‐NPs on a wide variety of microorganisms, such as bacteria Escherichia coli, Bacillus subtilis, Vibrio fischeri and Streptococcus aureus [12,13], cya‐ nobacteria Microcystis aeruginosa [14], microalgae Chlorella vulgaris, Pseudokirchneriella sub‐ capitata, Chlamydomonas reinhardtii, Chlorella pyrenoidosa and Coelastrella terrestris [13,15– 17,18–20], and picoplankton Picochlorum sp. [21]. These studies focused on the cellular Citation: Canuel, C.; Vaz, C.; Matias, W.G.; Dewez, D. Interaction Effect of EDTA, Salinity and Oxide Nanoparticles on Alga Chlamydomonas reinhardtii and Chlamydomonas euryale. Plants 2021, 10, 2118. https://doi.org/10.3390/ plants10102118 Academic Editor: Dariusz Latowski Received: 9 September 2021 Accepted: 2 October 2021 Published: 6 October 2021 Publisher’s Note: MDPI stays neu‐ tral with regard to jurisdictional claims in published maps and institu‐ tional affiliations. Copyright: © 2021 by the authors. Li‐ censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con‐ ditions of the Creative Commons At‐ tribution (CC BY) license (http://crea‐ tivecommons.org/licenses/by/4.0/).