Evaluation of Metal Toxicity in Chlorella kessleri from the Perspective of the Periodic Table

The toxicities of 33 metals (36 species of metal ions) in Chlorella kessleri were investigated and compared to several parameters such as ion radii, stability constants with several ligands, solubility products, and heats of formation (enthalpy). Although a universal parameter that could explain the toxicities of all of the metal ions was not identified, the Irving–Williams series and the HSAB (hard and soft Lewis acidity and basicity) are related to the toxicity of metal ions. With regard to aluminum group elements, the amount of free ion determines the toxicity. Metal absorption was also investigated, including its time dependence (transient absorption). The absorption (adsorption) of anionic species (oxoacid) is lower than that of cationic species which in some cases shows a high collection rate of over 90%. Furthermore, absorptivity varies during the different growth regimes of the cell. Among green alga, Chlamydomonas reinhardtii is much more resistant to metal toxicity than Chlorella kessleri. Intracellular distribution of zinc was also determined by using a zinc-fluorescent probe under a confocal laser microscope, and the result shows the intracellular distribution of pH could be an important factor for the intracellular distribution of zinc.