Phytoremediation of Metal-Polluted Ecosystems: Hype for Commercialization

Air, water, and soil are polluted by a variety of metals due to anthropogenic activities, which alter the normal biogeochemical cycling. Biodiversity has been employed widely by both developed and developing nations for environmental decontamination of metals. These technologies have gained considerable momentum in the recent times with a hype for commercialization. The United States Environmental Protection Agency's remediation program included phytoremediation of metals and radionuclides as a thrust area to an extent of 30% during the year 2000. Plants, that hyperaccumulate metals, are the ideal model organisms and attracted attention of scientists all over the world for their application in phytoremediation technology. Metal hyperaccumulators have the ability to overcome major physiological bottlenecks. The potential of hyperaccumulators for phytoremediation application relies upon their growth rates (i.e., biomass production) and metal accumulation rate (g metal per kg of plant tissue). The two primary reasons, that are limiting global application of this technology, are the slow growth rates exhibited by most naturally occurring metal hyperaccumulators and the limited solubility of metals in soils (i.e., the high affinity of metal ions for soil particles). Phytoremediation applications, relevance of transgenic plants for metal decontamination, chelate enhanced phytoremediation, chemical transformation, molecular physiology and genetic basis of metal hyperaccumulation by plants, commercialization hype for the phytoremediation technology are reviewed.