Study of bioaccumulation of Cr, Ni and Zn by the green alga Desmodesmus subspicatus and assessment of the toxic effect of selected elements and their mixtures on algae cells

Abstract

Toxicity assessment of K2Cr2O7, ZnCl2 and NiCl2.6H2O focusing on the green unicellular alga Desmodesmus subspicatus showed that Ni was the most toxic (EC50 = 0.121 mg L−1), followed by Cr (EC50 = 0.357 mg L−1) and Zn (EC50 = 0.968 mg L−1). The alga was exposed to solutions of the individual metals and their mixtures (Zn + Ni, Zn + Ni + Cr). After 48, 72 and 96 h of exposure, the accumulation of Zn, Ni and Cr in algal cells was assessed. Moreover, the change in toxicity of the metals, the concentration of selected biogenic elements (Ca, Na, Mg, S, K, P, Mn) in algal cells and the rate of metal removal from the solutions were also analysed. In the case of single-metal solutions, for Zn and Cr, the toxicity and accumulation in algal cells decreased over the 96 h of the experiment, whereas for Ni as well as for the binary and ternary mixtures the toxicity and accumulation increased. Significant correlations between the amount of metals accumulated in the cells and the inhibition of growth rates were observed. The content of selected biogenic elements in algal cells decreased over time in all treatments with added metals as well as in the control group, and after 96 h was higher in all treatments with addition of Ni compared to the control group and single-metal solutions of Zn and Cr. The highest removal of the metal from the solution occurred in the case of the single metal solution of Zn, where 83.4% of Zn was removed from the solution in 96 h.