Phytoremediation of metals and radionuclides

Abstract

The air, water and soil have been contaminated as a result of industrial revolution and increased urbanization of the landscape. Excavation and deposition of contaminated soil in depositories are of common occurrence and physico-chemical methods are normally used for the remediation of contaminants. Recently, bioremediation-the use of biological agents for remediation of soils and solutions has received a lot of attention (Suresh and Ravishankar 2004). In our laboratory, a variety of biological systems of microbes and plant organs are being investigated for the treatment of heavy metal and radionuclide waste (Bhainsa and D,Souza 1999; Sar and D,Souza 2001 2002; Melo and D,Souza 2003; Eapen et al. 2003). Phytoremediation-the use of plants for environmental clean-up, offers an attractive, environmental friendly and cost-effective approach to remediate metal and radionuclide polluted solutions and soil (Entry et al. 1997, Zhu and Shaw 2000) (Table 1). Plants have constitutive (present in most phenotypes) and adaptive (present only in tolerant phenotypes) mechanisms for accumulation or tolerance of high contaminant concentration in their rhizosphere. A phytoremediation system capitalizes on the synergistic relationship among plants, micro-organisms, water and soil that have evolved naturally in wetlands and upland sites over millions of years. This approach makes use of the plants ability to extract, concentrate and metabolize materials from air, water and soil (Salt et al. 1995). Plants can be described as solar-driven pumping stations (Cunningham et al. 1995) and possess homeostatic mechanisms to maintain the correct concentrations of essential metal ions in different cellular compartments and to minimize the damage from exposure to non-essential metal ions. Phytoremediation is an umbrella term which covers several plant-based approaches for cleaning up contaminated environments and includes phytoextraction, the accumulation of high concentrations of metals in plant biomass; rhizofiltration, removal of contaminants from aqueous wastestreams by adsorption into plant roots; phytovolatalization, which includes volatilization into the air through plants, phytodetoxification, which involves the ability of plants to change the chemical species to a less toxic form and phytostabilization, where plants immobilize contaminants chemically and physically at the site, thereby preventing their movement to the surrounding areas. © 2007 Springer-Verlag Berlin Heidelberg.