Correlation and Prediction of Metal Toxicity to Aquatic Biota

Abstract

Published data on the toxicity of metal ions to aquatic biota, in particular Daphnia magna, were analyzed for their correlation with ion specific physico-chemical parameters. Significant correlations were obtained for three groups of ions with similar electron configurations in the outer orbitals. Group I ions include Na (I), Be (II), Ba (II), Al (III), and Cr (VI) with inert gas-like electron configurations; group II ions include Cr (III), Mn (II), Fe (III), Co (II), Ni (II), Cu (II), Zn (II), As (V), Cd (II), Pt (IV), Au (III), and Hg (II) with partially or completely filled d electron orbitals; group III ions include Sn (II), As (III), Se (IV), and Pb (II), with filled d and s, but unfilled p electron orbitals. The toxicity of an ion within a group can be calculated from the general equation[Formula: see text]where pT is the negative logarithm of a metal ion concentration with a certain toxicity in mol∙L−1; AN is the metal's atomic number; ΔIP is the difference between the ion's ionization potential with the oxidation number (OX) and the ionization potential of the next lower oxidation number (OX − 1) in electron volts (eV); and ΔE0 is the absolute value of the electrochemical potential between the ion and the first stable reduced state. The values for the constants a0, a1, and a2 depend on the group of ions, the biota, and the particular toxic effect determined. The equation is applied to predict the toxicities of other ions under similar test conditions.Key words: toxicity, metals, ions, correlations, Daphnia magna, aquatic tests