Estimation of Phytofiltration Potential for Cu and Zn and Relative Growth Response of Azolla japonica and Azolla Pinnata

Microcosm experiments were conducted under controlled environmental conditions in order to estimate growth response and phytoremediation ability of A. japonica and A. pinnata. Plants were exposed to solutions of different Cu-concentrations [Cu] (0, 1, 2, 5 and 7 mg L-1) and Zn-concentrations [Zn] (0, 0.5, 1, 2 and 4 mg L-1) under different incubation periods (0, 3, 6, and 12 days) along with control treatments. Lower metal concentrations [< 2 mg L-1 (Cu) and < 1 mg L-1 (Zn)] enhanced plant growth; however, growth was significantly inhibited at higher concentrations during Longer Incubation Periods (LIPs). Azolla species showed substantial metal removal capacity (on an average, Removal efficiency> 80% for Cu and > 60% for Zn during LIPs). The higher the metal concentrations with LIPs, the higher the metal removal amounts. Plant`s exposure to high (Cu) and (Zn) during LIPs showed changes in color and detachment of the roots that might result in plant death due to phytotoxicity effect. Highly significant relationships (r= 0.91** & 0.82** for Cu and r= 0.93** & 0.92** for Zn in case of A. pinnata and A. japonica, respectively) between metal removal amounts and metal concentrations in biomass indicated that phytoaccumulation was the possible mechanism for phytoremediation because the metals removed from solutions were actually accumulated into the plant`s biomass. The high value of bioconcentration factor indicated that Azolla species were hyperaccumulators, and can be deployed effectively for phytofiltartion of Cu and Zn.