Phytoremediation potential of naturally growing weed plants grown on fly ash-amended soil for restoration of fly ash deposit.

Sida acuta Burm. f. and Cassia tora (L.) Roxb were identified as dominant plant species in fly ash deposit of NALCO, Koraput, India in our earlier study. However, little information is available on their physiological response to metal stress under fly ash amended soil. A pot experiment was designed with fly ash amended soil to assess its growth, photosynthesis, antioxidant defense along with metal accumulation. Addition of fly ash (50%) in soil amendments not only improved the soil physico-chemical characteristics but also increased the plant biomass. The studied plants were found to be a potential metal tolerant as metal tolerance index was more than 100% under fly ash amended soil. Leaf photosynthetic rate, chlorophyll content and photosystem II activity were not significantly changed under low level of fly ash amended soil (50%) compared to the garden soil. The induction of some antioxidative enzymes such as superoxide dismutase, ascorbate peroxidase, Guaiacol peroxidase and catalase in studied plants under elevated fly ash indicates metal tolerance ability of this plant to oxidative stress. Based on the bioaccumulation factor (BCF) and transfer factor (TF), these plants can be used for the remediation of Mn, Cu, Zn, Fe and Cr from fly ash.