Interactions of copper and lead with Nostoc muscorum

Experiments were conducted to evaluate the effects of cell concentration, time of exposure, cellular activity and solution chemistry, on Pb (10^-6 M) and Cu (10^-5 M) uptake by the alga Nostoc muscorum. Surface equilibrium, with respect to aqueous metal levels, was established within an equilibration period of 8 h and maximum metal removal was observed in the pH range of 7.5 to 8.0. The observed removal of Cu and Pb from solution was similar to adsorption observed for inorganic surfaces at pH values less than 8.0. Removal of metallic ions decreased at pH values greater than 8.0 which was thought to be due aqueous complexation with organic extracellulair material. The extent to which the cells were able to remove trace metals from solution in the presence of citrate, sulfate, and Ca ion (10^-3 M) was also evaluated. Additions of citrate and Ca ion mitigated metal uptake by algal suspensions. The presence of sulfate resulted in a reduction of Cu removal below pH values of 5.6 but enhanced the removal of Pb over the entire pH range. The chemical equilibrium model MINEQL was utilized to compare theoretical and observed phenomena so that possible mechanisms for metal-cell interactions could be assessed.