The effect of Cd(II) complexes with nicotinamide (NA) on microalgae growth, production of chlorophylls, oxygen evolution and Cd adsorption

The effects of Cd [Cd(NO3)(2)] and its complexes with nicotinamide (NA) [Cd(ac)(2)(NA)(2), Cd(NCS)(2)(NA)(2), Cd(NCSe)(2)(NA)(2)] were examined by using the algae Scenedesmus quadricauda and Chlorella vulgaris as a function of Cd speciation in a well-defined aqueous medium. The parameters observed during the experiments were algal growth inhibition, chlorophyll a and b content, oxygen evolution and Cd adsorption by algal cells. With regard to growth and production of chlorophylls (Chla, Chlb), the most toxic compound was Cd(NO3)(2). On the basis of EC50 values for these parameters, the following rank order can be arranged for both algae: Cd(NO3)(2) > Cd(ac)(2)(NA)(2) > Cd(NCS)(2)(NA)(2) > Cd(NCSe)(2)(NA)(2). While Cd(NO3)(2) in EC50 concentration for algal growth also reduced oxygen evolution nearly by half, all Cd(II) complexes used in EC50 concentrations for the same parameter reduced oxygen evolution less. When a comparison was done for Cd(NO3)(2), all Cd(II) complexes stimulated oxygen evolution in both algal species. Base on the adsorbed Cd quantity, the tested compounds for both algae could be arranged in the following sequence: Cd(NO3)(2) > Cd(ac)(2)(NA)(2) > Cd(NCS)(2)(NA)(2) > Cd(NCSe)(2)(NA)(2). The results confirmed that the adsorbed Cd amount markedly exerted its influence on algal growth and intensity of their physiological processes. Higher sensitivity was confirmed for alga S. quadricauda, which adsorbed a higher amount of Cd, and reduction of all observed parameters in this alga was more intensive than in C. vulgaris. As less toxic for both algae was confirmed the complex Cd(NCSe)(2)(NA)(2).