Individual and combined effects of cadmium and copper on the growth response of Chlorella vulgaris

The individual and combined effects of cadmium and copper on the growth response of the green alga, Chlorella vulgaris, were examined. The effects of pH alone, and in combination with copper were also evaluated. An increase in cadmium and copper concentrations caused a significant reduction in the growth of C. vulgaris cells, and the corresponding EC₅₀ values were 1.02 and 4.01 mg L^-1, respectively. For a pH range of 2-7, the inhibitory effect due to increased copper concentrations (coupled with the resulting drop in pH) was significantly higher than the impact due to increased acidity (by addition of HCl) alone. At lower metal concentrations (5 mg L^-1 Cu + < 2 mg L^-1 Cd or 2.5 mg L^-1 Cd + < 4 mg L^-1 Cu), a combination of copper and cadmium appeared to have a stronger inhibitory effect on cell growth than that of a single metal. In contrast, at higher metal concentrations (5 mg L^-1 Cu + > 2 mg L^-1 Cd or 2.5 mg L^-1 Cd + > 4 mg L^-1 Cu), the effect of a single metal exhibited a significantly stronger effect compared to a combination of the two metals.