Cadmium binding ability of the blue-green alga Hapalosiphon welwitschii Nägel under controlled conditions

Abstract

The ability of the blue-green alga Hapalosiphon welwitschii Nägel (a cyanobacterium) to bind cadmium from its medium was tested in cultures exposed to different metal concentrations (0.5, 1.5, 2.5, 3.5, 4.5, 5, 6, 8, 10 and 12 ppm). The amount of cadmium removed was shown to be time and concentration dependent. With increasing cadmium concentrations of 0.5 to 10 ppm, significant levels of the heavy metal were detected on the cell wall. However, at 12.0 ppm, a higher amount of the heavy metal was detected inside the cytoplasm. The cells also exhibited efflux of cadmium after 24 and 48 h of incubation. The presence of Cu2+ significantly increased the amount of bound cadmium. On the other hand, the ions Co2+, Mg2+, and Ni2+ significantly decreased the amount of cadmium bound to the cells most probably because of competition for binding sites resulting in inhibition of cadmium binding. The maximum binding of cadmium by the cells was at pH 9, but was not significantly T different from the binding observed in cultures grown at the optimum pH of 7.5. However, there was a significant decrease in cadmium binding when the pH of the medium was acidic (pH 3 and pH 5). The results obtained from this study may provide baseline information for further studies on the potential of the blue-green alga H. welwitschii to clean up cadmium contaminated areas.