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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Adaptive Cropping Systems Laboratory » Research » Publications at this Location » Publication #334592

Title: Phytoremediation and Phytomining: Status and Promise

Author
item Chaney, Rufus
item BAKLANOV, ILLAY - University Of Maryland

Submitted to: Advances in Botanical Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2016
Publication Date: 6/1/2016
Citation: Chaney, R.L., Baklanov, I.A. 2016. Phytoremediation and Phytomining: Status and Promise. Advances in Botanical Research. 83: doi.org/10.1016/bs.abr.2016.12.006.

Interpretive Summary: Soil with high concentrations of metals such as Zn, Cd, Ni, Pb, etc., can cause adverse effects on plants and animals. Removal and replacement of the contaminated soil would often be extremely expensive and cause great disturbance of the local ecosystem. An alternative to “dig and haul” is growing metal hyperaccumulator plants for harvest as a hay crop to remove the metals from the soil (phytoextraction) or adding soil amendments to make the metals unavailable (phytostabilization). The ability of hyperaccumulator plants to accumulate 100-times higher leaf metal concentrations than do crop plants allows growth and harvest of these species to conduct “phytoextraction” of the soil metal. If the metal in the harvested plant biomass would have high economic value, the technology is called “phytomining.” Unfortunately, no plant accumulates high enough Pb from field contaminated soils to achieve useful Pb phytoextraction. With growth of the exceptional Cd accumulating Noccaea caerulescens (alpine pennycress) from southern France, with proper fertilizers, grass herbicides pH adjustment and where necessary application of fungicides, enough Cd can be removed to achieve decontamination in a few years. A Cd-accumulating rice cultivar has also been developed for this use; the rice is better adapted to a subtropical climate and soils and pennycress to temperate climates. But until governments order or pay for Cd phytoextraction, this effective technology will not be commercialized. On the other hand, Ni accumulation by plants can reach higher than 2% Ni in leaf dry matter, can be grown on extensive ultramafic soils with identified agronomic management and can yield more dollar value than crop plants especially considering the low yields of crop species on these soils. Alternative methods to recover the Ni as metal by smelting the plant ash, or chemical processing to produce nickel-ammonium-sulfate illustrate use of this technology. Several plants may accumulate Zn, Se, Ni or Mn and become a fertilizer or feed additive which meets “Organic” limitations.

Technical Abstract: Phytoremediation of inorganics is comprised of technologies to protect the environment from contaminated soils. This broad group of technologies includes phytoextraction (removal from soil), phytomining (accumulating economic metal value in plant biomass) and phytostabilization (limiting plant metals and soil metal uptake and/or bioavailability using plants and soil amendments). As agronomic technologies, selection of plant genotypes, management of soil properties, appropriate use of fertilizers and soil pH adjustment amendments are required for optimum effectiveness. Phytoextraction depends on the availability of plants which can accumulate and tolerate ~100-fold higher metal concentrations than tolerated by common crop species. Unless a plant can accumulate over 1% (10 g kg-1) of a metal in dry shoot biomass, it is unlikely to remove metals rapidly enough to support economic remediation. For element cases where contamination is low (Cd), plants which accumulate over 1000 µg g-1 may be able to achieve adequate phytoextraction. In the case of Ni, the combination of extensive ultramafic soils rich in Ni, and natural hypernickelophores (accumulate over 10 g Ni kg-1) with high harvestable biomass yield allows a phytomining technology to be profitable. Increasing knowledge of the biochemistry and genetic mechanisms used by hyperaccumulator plants portend the day that high biomass element hyperaccumulator plant genotypes can be constructed for soil remediation in all climatic zones.