Removal of heavy metals by two free floating aquatic macrophytes

A concentration-dependent decrease in biomass, protein, RNA, DNA, and nutrient (NO3(-) and PO4(3-)) uptake of Lemna minor and Azolla pinnata by Cr, Ni, and Zn was detected. Cr was found to exert maximum toxicity followed by Ni and Zn. Metal uptake was dependent on time and concentration of metal in the external medium. Both the macrophytes, however, showed preference for Zn followed by Ni and Cr. The uptake kinetics also revealed a low Vmax and high Km for Cr. L. minor was more efficient in accumulating Zn and Cr than A. pinnata in Ni. Compared to immobilized algae and bacterial capsules the test macrophytes showed a greater efficiency for metal removal.