Effect of environmental conditions on biouptake of Cu and Pb from natural freshwaters by Chlamydomonas reinhardtii: a case study, Litani River, Lebanon

摘要

Of the unicellular green algae species, Chlamydomonas reinhardtii has only recently gained greater attention for the treatment of heavy metal contamination in aqueous solutions. In the present study, C. reinhardtii was used to remove Cu and Pb metal ions from the Litani River in Lebanon. Three samples were collected from three different sites located along the tributaries of Litani. Short-term (40min) metal biouptake experiments were performed using 0.2g L-1 of freeze-dried and living algal cells. In the studied samples, dead cells showed higher removal efficiency for both metal ions than living cells. The percentage removal of dead algae for Cu (28.66%) is about 1.8 times higher than that of living cells (16%). For Pb, biosorption (23.4%) is about 2.75 times higher than bioaccumulation (8.5%). Water chemistry significantly affects metal speciation, bioavailability, and biouptake by living and dead cells. As predicted by Visual MINTEQ program, only very small fractions of Cu and Pb were present as free ions with the majority being bound to humic substances (HS) or carbonate ligands. PbCO3 and CuCO3 dominated in water samples containing very low amount of organic compounds. As stated by the free ion activity model (FIAM) and the biotic ligand model (BLM), Cu uptake seems to increase with an increase in the free Cu2+ concentration in water and it is dependent on ligands complexation and co-cations competition effects. However, equilibrium models cannot explain the bioaccumulation results obtained for Pb. Although further investigations are needed, the obtained results are very promising as a starting point for a potential application of these micro-organisms as an efficient and economic biomaterial for the removal of heavy metals from metal-contaminated freshwaters.