Phytoremediation of the metalloid selenium in soil and water

Toxic heavy metal selenium (Se), is constantly released into the environment. There is an urgent need to develop low-cost, effective, and sustainable methods for Se removal. Plant-based approaches, such as phytoremediation, are relatively inexpensive since they are performed in situ and are solar-driven. In this review, we discuss specific advances in plant-based approaches for the remediation of Se-contaminated water and soil. Dilute concentrations of Se contaminants can be removed from large volumes of wastewater by constructed wetlands. We discuss the potential of constructed wetlands for use in remediating Se in agricultural drainage water and industrial effluent, as well as concerns over their potential ecotoxicity. In upland ecosystems, plants may be used to accumulate Se in their harvestable biomass (phytoextraction). Plants can also convert and release Se in a volatile form (phytovolatilization). We discuss how genetic engineering has been used to develop plants with enhanced efficiencies for phytoextraction and phytovolatilization. For example, Se-hyperaccumulating plants and microbes with unique abilities to tolerate, accumulate, and detoxify Se represent an important reservoir of unique genes that could be transferred to fast-growing plant species for enhanced Se of phytoremediation. There is also a need to develop new strategies to improve the acceptability of using genetically engineered plants for Se of phytoremediation.