Assessment and augmentation of phytoremediation potential of selected angiosperms

Abstract

Phytoremediation is an appropriate strategy for the removal of heavy metals, such as Cd and Pb, from contaminated matrices. In this context, the present study set out to investigate the Cd and Pb phytoremediation potential of the plants Alternanthera brasiliana, Chrysothemis pulchella, Croton hirtus, Leucas zeylanica, Solanum trilobatum, and Strobilanthes alternata. The results revealed Strobilanthes alternata as the most appropriate plant for phytoremediation of Cd and Pb (phytostabilization). It was also found that the plant could tolerate concentrations as high as 250 mg/kg CdCl2 and 500 mg/kg PbCl2, and therefore, these concentrations were chosen for further studies. The study also evaluated the efficiency of the compounds 6-BAP, Kinetin, Gallic acid, Humic acid, and Vanillin in enhancing the Cd and Pb phytostabilization potential of S. alternata. 6-BAP (25 ml of 25 ppm) was found to be the most promising compound for enhancing the Cd phytostabilization potential of S. alternata. Since none of the compounds could enhance the Pb phytostabilization potential of S. alternata, further studies on Pb phytoremediation were dropped. Hence further studies comprising morphological, physiological, biochemical, ultrastructural and gene expression analyses were conducted with Control plants, 6-BAP treated plants (25 ml of 25 ppm 6-BAP), Cd treated plants (250 mg/kg CdCl2) and Cd+6-BAP treated plants (250 mg/kg CdCl2 + 25 ml of 25 ppm 6-BAP). All these studies revealed that, in addition to augmenting the Cd phytostabilization potential, 6-BAP had Cd stress alleviating effect on S. alternata. This is evident from the positive alterations in the morphological, physiological, anatomical, ultrastructural and molecular level characteristics in Cd+6-BAP treated plants when compared to the Cd only treated plants. Hence, this study strongly recommends 6-BAP administration as a suitable amendment to improve the phytoremediation potential of S. alternata without severely affecting the normal metabolic processes of the plant. As a result, 6-BAP-assisted phytostabilization using S. alternata can be considered a viable technique for cleaning up Cd- contaminated soil.