Growth Responses of Microalgae to Multiple Metal Ion Stress

M. Pratima, S.B. Angadi and R.D. Mathad

ABSTRACT

The effect of four heavy metals (nickel, zinc, cadmium and lead) were studied, individually and in combination, on the diazotropic cyanobacterium Hapalosiphon stuhlmanni and the photosynthetic green alga Scenedesmus quadricauda. The interactive effect of heavy metals was investigated over the concentration range of 0.1-15.0 g L ¹ by adopting an exponential cell growth model. The cultures treated with higher metal concentrations were decolorized and developed enlarged and deformed cells. The interactive effect of metals on both the algae was mostly antagonistic in the concentration range 0.1-15.0:0.1-10.0 mg L ¹ of Pb:Ni and 0.1-3.0:0.2-15.0 mg L ¹ of Cd:Zn. However the interactive effect of lead and nickel on the dry weight and chlorophyll a content of Scenedesmus quadricauda was synergistic at higher metal concentrations. The degree of antagonism varied with the bimetallic concentrations and was, in fact, lowest for the higher metal concentrations. The degree of antagonism due to combination of lead-nickel and cadmium-zinc was higher in Scenedesmus quadricauda than in Hapalosiphon stuhlmannii. The antagonistic behavior was explained to be due to the adsorption of one of the metals hindering the sorption of the other and the synergistic effect, due to adsorption of one enhancing the permeability to the other metal. The varied interactive behaviors were possibly because of either the formation of complexes with the algal exudes or the coagulation and co-precipitation of the metals with each other.