Submitted to: Proceedings of the International Workshop on Current Developments in Remediation of Contaminated Lands
Publication Type: Abstract only
Publication Acceptance Date: 10/7/2005
Publication Date: 10/27/2005
Citation: Chaney, R.L., Angle, J.S., Wang, A., Mcintosh, M.S., Broadhurst, L., Reeves, R.D. 2005. Phytoextraction of soil cd, ni and zn using hyperaccumulator plants to alleviate risks of metal contaminated soils requiring remediation. [abstract]. Proceedings of the International Workshop on Current Developments in Remediation of Contaminated Lands. Pulaway, Poland, October 27-29, 2005. p. 39. Interpretive Summary: .
Technical Abstract: Some soils contain levels of metals which threaten crop yield or food safety. Rare plant species hyperaccumulate some elements in their aboveground biomass, offering us an agronomic tool to remediate by phytoextraction of soil elements. Although high soil levels of elements such as Pb and Cr may comprise concern, no hyperaccumulator plant exists. For Cd, Zn, Ni, Se, As, Co and possibly some other elements, natural metal hyperaccumulator plant species have been found and grown experimentally. To build commercially useful phytoextraction technologies, one must work out the agronomy of the plant, breed improved cultivars, and show that the overall technology is effective and profitable. I suggested phytoextraction of soil Ni with recovery of the Ni from the biomass in 1980, and started working to develop phytoextraction technology in 1991. We first illustrated Cd and Zn phytoextraction by Thlaspi caerulescens. We tested diverse genotypes and found (with Roger Reeves) that populations from southern France accumulated about 10-times higher levels of Cd from the same soil as the ‘Prayon’ population first studied. We are breeding improved cultivars and demonstrating the agronomy of practical Cd phytoextraction without harming soil microbes. Our latest test showed 45% removal of soil Cd by one 6-month cropping of a soil with 5 mg Cd/kg, and 37% removal of total Cd from a soil with 25 mg Cd/kg. Two kinds of Cd contaminated soils comprise risk which requires remediation: 1) rice soils contaminated by geogenic (contain about 100-times higher Zn than Cd) or other Cd sources; and 2) other foods and tobacco grown on soils with high Cd:Zn source. Because governments have not ordered soil Cd remediation, no market for Cd phytoextraction has yet developed. Extensive Cd contaminated rice paddy soils in Asia threaten human health and require remediation. We also domesticated Alyssum murale as a commercial Ni phytomining crop. Ni has more value than most elements known to be hyperaccumulated, about $16/kg. Numerous species of Alyssum accumulate higher than 1% Ni in shoots. We collected diverse germplasm and tested their growth and Ni accumulation ability when grown on serpentine soil in Oregon. The best genotypes accumulated as high as 2.7% Ni in aboveground biomass. This species is tall enough to harvest with commercial hay making equipment. Yields for high Ni types can exceed 20 t/ha depending on fertility and water supply. This species is perennial, and vernalization is induced by cold short days. Thus one harvest per year is made before leaves start to drop off flowering plants. Biomass can be baled, then burned to generate energy and ash, and the ash marketed as a high grade Ni ore. The ash is perhaps the best Ni ore offered for sale; plant nutrients do not interfere with recovery of Ni from the ash by traditional smelting technologies in a electric arc furnace. Because of the high value of Ni metal, and the low cost of farm production of Alyssum murale, this crop offers a commercial opportunity. Our patents on the Ni phytomining technology and cultivars have been licensed to Viridian Environmental LLC who provided funding to develop the technology.