Tolerance ofChlorella vulgaris for metallic and non-metallic ions

The well-known, extreme sensitivity of algae towards Cu⁺⁺ ions prompted a systematic investigation of the tolerance ofChlorella vulgaris for both metallic (49) and non-metallic (7) ions. With thirty metals forming weak bases, pH effects were to some extent super-imposed on the toxic effects of the metal ions themselves. With the elements U, Zr, V and Sb, oxy-compounds had to be used. The elements Mo, W and Bi were tested as components of anions.From the metals that form strong bases, the salts of Na, K, Rb, Ca, Sr and Mg were tolerated in high concentrations; the maximum values of these ranged from 0.11 – 0.98 g at/liter. Notwithstanding some unavoidable simplifications of the experimental technique, it could be concluded from the results that in four intermetal groups, arranged according to I.U.P.A.C., toxicity has a definite tendency to increase with increasing atomic number. This held for the series: Na, K, Rb, Cs; Mg, Ca, Sr, Ba; Zn, Cd, Hg; Al, In, Tl. In like manner, the rare earths were found to be more toxic than the alkaline earth metals.Co, Ni and Cu completely inhibit growth at very low concentrations ranging from 4.2×10^–6–2×10^–5 g at/liter; in view of the relatively low atomic numbers of these metals, the toxicity must be regarded as specific (algotoxicity).Among the non-metals, Sb and As proved highly toxic. Fluoride ions were considerably more toxic than chloride and bromide ions.