RESEARCH ARTICLE Chronic toxicity of 50 metals to Ceriodaphnia dubia Akira Okamoto 1 | Shigeki Masunaga 2 | Norihisa Tatarazako 1,3 1 Graduate School of Frontier Science, The University of Tokyo, Kashiwa, Chiba, Japan 2 Graduate School of Environment and Information Sciences, Yokohama National University, Hodogaya, Yokohama, Kanagawa, Japan 3 Center for Health and Environmental Risk Research, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan Correspondence Norihisa Tatarazako, Graduate School of Agriculture, Ehime University, Ehime 790-8566, Japan. Email: tatarazako.norihisa.wn@ehime-u.ac.jp Abstract Metals are essential elements for human life but may cause disorders when exposure is excessive. Previously, we reported on the acute toxicity of 50 metals; however, the chronic toxicity data of some metals are not available. Therefore, we conducted chronic toxicity tests to determine the effects of 50 metals on the water flea, Ceriodaphnia dubia. The IC 20 of 20 metals (Be, Sc, Cr, Co, Ni, Cu, Zn, Y, Ru, Ag, Cd, In, Te, W, Os, Pt, Au, Hg, Tl and Pb) were <100 μg/L; nine metals (Al, V, As, Se, Zr, Nb, Rh, Sb and Bi) were 100 ≤ IC 20 < 1000 μg/L; 16 metals (Li, Mg, K, Ti, Mn, Fe, Ga, Ge, Rb, Sr, Mo, Sn, Cs, Ba, Re and Ir) were 1000 ≤ IC 20 ≤ 100 000 μg/L; and two metals (Na and Ca) were >100 000 μg/L. Three metals (Pd, Hf and Ta) did not show IC 20 at the upper limit of respective aqueous solubility, and IC 20 s were not obtained. The maximum test concentrations (almost aqueous solubility) of Pd, Hf and Ta were 83, 2400 and 5.3 μg/L, respectively. These data show the high correlation between our IC 50 s for C. dubia and those for Dahpnia magna published previously. The IC 50 s of 47 metals were not correlated with electronegativity, first ionization energy, atomic weight, atomic number, covalent radius, atomic radius or ionic radius. KEYWORDS acute toxicity, Daphnia, electronegativity, LOEC, NOEC, physiological toxic effect, reproduction 1 | INTRODUCTION Metals are essential elements for human life and physiological functions. Some metals are essential elements required by humans, and most are used in electrical household appliances, electrical equipment, cars and catalysts (Herincs, Puschenreiter, Wenzel, & Limbeck, 2013; Singh & Rajaraman, 2014; Wu et al., 2013). Solar power has been attracting attention as an alternative energy to fossil fuels. Cu and the minor metals In, Ga and Se are used as semiconductors to increase the electric power generation rate of solar panels (Eisenberg, Yu, Lam, Ogunseitan, & Schoenung, 2013). The lifetime of a solar panel is 20-30 years. Consequently, in the near future, metals present in solar panels may be released as elec- trical waste (E-waste) into the environment, although the rough part of valuable materials (Cu and other precious metals) can be recovered from E-waste by dismantling, crushing and combustion (Hu et al., 2013; Huo et al., 2007; Leung, Luksemburg, Wong, & Wong, 2007; Man et al., 2011). High concentrations of Cr, Co, Zn, Cd, Cu, Ni and Pb have been detected in dust in some developing countries (Banerjee, 2003; Leung, Chan, Lam, & Chan, 2013; Leung, Duzgoren-Aydin, Cheung, & Wong, 2008; Lopez et al., 2011; Luo, Yu, Zhu, & Li, 2012; Madany, Akhter, & Jowder, 1994; Ren et al., 2013; Shi, Chen, & Wang, 2013; Wong et al., 2007a), and recovery procedures for these are currently being conducted. In addition, the increased use of Sb as a flame retardant has caused an increase in Sb soil concentration (Wong et al., 2007b). As the demand for metals increases, environmental pollution must be considered. Toxicity testing has already been conducted for most metals detected in the environment; however, the toxic- ity of some metals can change because of the chemical character- istics of solutions, including pH, hardness and dissolved organic carbon (De Schamphelaere & Janssen, 2004). Thus, toxicity testing Received: 14 June 2020 Revised: 24 July 2020 Accepted: 27 July 2020 DOI: 10.1002/jat.4049 J Appl Toxicol. 2020;1–12. wileyonlinelibrary.com/journal/jat © 2020 John Wiley & Sons, Ltd. 1