Role of Hyperaccumulators in Phytoextraction of Metals From Contaminated Mining Sites: A Review

Accumulation of heavy metals in selective locations of the environment has been attracting considerable public attention over the last decades. The conventional clean-up technologies to extract and remove heavy metals from mining sites are either inadequate or too expensive for developing countries. In the past decades, research efforts have been directed toward phytoextraction by using hyperaccumulators as an alternative, low-cost means of extracting heavy metals from the metal contaminated mining sites. Hyperaccumulating plants are used to transport and concentrate metals from soil into the harvestable parts of plants such as roots and aboveground shoots. Such harvestable biomass is ashed so that the ash can be disposed or even better recycled in metal processing industry for biorecovery of precious and semiprecious metals. This is a cost-effective, environmentally friendly, aesthetically pleasing approach most suitable for developing countries. The authors report the characteristics and mechanisms of hyperaccumulation in metal extraction and also classify the types of hyperaccumulation on the basis of bioavailability of metal to the plant. They also give insight into the role of genetic engineering for enhancing the efficiency of hyperaccumulation in metal extraction.