Hyperaccumulation of cadmium and nickel by Azolla species

Azolla, a small N-fixing and free floating aquatic fern exhibits high growth rate coupled with increased capacity to accumulate nutrients and metal ions in its biomass from flood waters. This trait can be employed for phytoremediation of metal contaminated wastewaters. In the present study, hyper accumulation of toxic heavy metals, Ni (Nickel) and Cd (Cadmium) by three species of Azolla (A. microphylla, A. filiculoides and A. pinnata) resulted in inhibited growth of these species. The concentration of Ni in biomass at applied levels of Ni ranged between 0.7–2.8% of dry weight and for Cd between 0.02–0.2%. Bioconcentration factor (BCF) up to 277 for Cd and 131 for Ni was observed. Metal concentration in biomass increased as metal levels in environment went higher and growth was severely inhibited. The necrosed biomass of Azolla was able to accumulate high amounts of Ni and Cd. The studies suggest that Azolla biomass can thus be employed for bioconcentration of Ni and Cd from wastewaters.