Toxicity of nickel, zinc, and cadmium to nitrate uptake in free and immobilized cells of Scenedesmus quadricauda.

We examined the influences of three trace metals on the accumulation of a major nutrient (NO3-) in Scenedesmus quadricauda. A comparative study on metal-nutrient interaction in free and immobilized states of algal cells was conducted. The effect due to interaction between different variables (cell state type, metal type, and metal dose) was studied to assess the variation in the nitrate uptake by free and immobilized cells. The results analyzed by ANOVA (three-way) (components: cell state type, metal type, and metal dose) confirmed that the inhibition of nitrate uptake by test metals was highly significant (P<0.001). Free and immobilized states of S. quadricauda responded differently (P<0.05, ANOVA) to the types of metal added. Uptake kinetics was studied by monitoring short-term uptake rates at different nutrient levels. Free and immobilized cells of the organism displayed noncompetitive modes of inhibition for Ni and Zn while a competitive mode of inhibition by Cd was observed in both free and immobilized states of the organism.