Phytoremediation of heavy metal-contaminated soil using bioenergy crops

Abstract

Heavy metal contamination of soils affects large areas worldwide. Excessive amount of metals, whether essential or nonessential, adversely affects the health of wildlife, humans, and plants and makes the land unusable for agricultural production. Phytoremediation, a sustainable, environment-friendly, and potentially cost-effective technology, can be used to decontaminate heavy metal-contaminated land. Use of nonfood, dedicated bioenergy crops for remediation of heavy metal-polluted sites has the advantage that biomass produced can be used to generate bioenergy, a cheaper, safer, sustainable, and renewable energy source compared to fossil fuels, avoids direct competition with food, and uses land unsuitable for growing food crops. Identifying dedicated bioenergy crops suitable for a particular metal-contaminated land and strategies to increase their phytoremediation potential are important for the success of this approach. Some dedicated bioenergy crops including poplars (Populus spp.), willows (Salix spp.), elephant grass (Miscanthus × giganteus), castor bean (Ricinus communis), and switchgrass (Panicum virgatum) can tolerate high concentrations of heavy metal, accumulate metal, and grow well on contaminated lands. Phytoremediation potential of these crops can be further improved by the effective use of metal solubilizing agents, endophytic bacteria, and genetic engineering. A better understanding of the mechanisms of heavy metal uptake, translocation, accumulation, and tolerance in normal and metal hyperaccumulator plants will help scientists to develop effective and economic transgenic bioenergy crops for remediation of heavy metals in soil.