Assessing the rhizofiltration potential of three aquatic plants exposed to fluoride and multiple heavy metal polluted water

Abstract

Heavy metals like arsenic, copper, lead and nickel and the non-metallic xenobiotic, fluoride are the major pollutants of aquatic ecosystems. All these pollutants exhibit high biomagnification along the food web and their consumption and usage have been widely warned against by almost all internationally regulated bodies. In order to alleviate the rising concern due to the use of polluted water, an eco-friendly, cheap and sustainable phytoremediative blueprint was designed by assaying the comparative rhizofiltration capacity of the three commonly found aquatic plants, viz., Azolla (water fern), Pistia (water lettuce) and Eichhornia (water hyacinth) in separate sets of polluted water samples. Interestingly, water lettuce exhibited highest phytoextraction and phytostabilization of arsenic, lead and fluoride, whereas water fern and water hyacinth ‘cleaned’ the nickel- and copper-polluted water sets, respectively with the highest efficiency among the tested species. Incidentally, this was due to the increased release of organic acids like citric and malic acids as root exudates which led to scavenging, root absorption/adsorption or sedimentation of the pollutants. Water lettuce was identified as an efficient hyperaccumulator of fluoride with a translocation factor of 5.0 and yet the overall biomass was unaffected due to phytostabilization of the toxicant. Due to significant bioaccumulation of the xenobiotics, the root and shoot length of the tested species were variably affected. Overall, the present work advocated the use of distinct plant species for efficiently ‘cleaning’ and de-polluting variable xenobiotic toxicants commonly available in the aquatic environment.