Chronic toxicity of 50 metals to Ceriodaphnia dubia

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 IC₂₀ 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 ≤ IC₂₀ < 1000 μg/L; 16 metals (Li, Mg, K, Ti, Mn, Fe, Ga, Ge, Rb, Sr, Mo, Sn, Cs, Ba, Re and Ir) were 1000 ≤ IC₂₀ ≤ 100 000 μg/L; and two metals (Na and Ca) were >100 000 μg/L. Three metals (Pd, Hf and Ta) did not show IC₂₀ at the upper limit of respective aqueous solubility, and IC₂₀ 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 IC₅₀ s for C. dubia and those for Dahpnia magna published previously. The IC₅₀ s of 47 metals were not correlated with electronegativity, first ionization energy, atomic weight, atomic number, covalent radius, atomic radius or ionic radius.