|Synkowski, Eva Claire|
Submitted to: Zeitschrift Fur Naturforschung
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2005
Publication Date: 4/24/2005
Citation: Chaney, R.L., Angle, J.S., Mcintosh, M.S., Reeves, R.D., Li, Y., Brewer, E.P., Chen, K., Roseberg, R.J., Perner, H., Synkowski, E. 2005. Using hyperaccumulator plants to phytoextract soil ni and cd. Zeitschrift Fur Naturforschung. 60C(3-4):190-198. Interpretive Summary: Phytoextraction is a promising technology to remove metals from contaminated soils. Evidence is presented that only hyperaccumulator plants are useful in phytoextraction. In some cases the value of the element in plant ash is high enough to conduct phytomining from mineralized or contaminated soils. Our team developed a complete technology for growing nickel hyperaccumulator Alyssum species which contained over 2% Ni in dry shoot biomass at harvest. All agronomic practices were developed for this new crop; improved cultivars were bred using normal plant breeding methods to combine yield potential and Ni bioaccumulation. Because the ash of these plants contain only plant nutrients, normal Ni smelting technologies were very effective in recovering the Ni from ash. Both the energy from burning the biomass, and the value of metals in the ash provide profit for practitioners. A new market for use of Ni rich biomass was discovered, the use of water extracts of ground biomass as a Ni fertilizer for Ni deficient pecan and River Birch grown in Ni deficient soils in Georgia, USA. Present efforts are focused on phytoextraction of soil Cd. Related studies have made it clear that rice soils, and soils contaminated by Cd sources with high Cd:Zn ratio may transfer enough soil Cd to humans to cause adverse effects. Thus rice, tobacco and high Cd:Zn soils require remediation. We have demonstrated a soil Cd phytoextraction technology using Thlaspi caerulescens from southern France which accumulate 10-20 fold higher Cd than previously studied genotypes. The methods used to find these high Cd genotypes, and the variability of plants from a population are presented. The cost savings by use of phytoextraction rather than soil removal and replacement is remarkable, on the order of 99% of the cost. Areas with Cd contaminated rice and tobacco soils are well known across Asia, but a market for the technology will not exist until governments require soil remediation to prevent future health effects of these Cd contaminated soils.
Technical Abstract: Two strategies of phytoextraction have been shown to have promise for practical soil remediation: domestication of natural hyperaccumulators, and bioengineering plants with the genes that allow natural hyperaccumulators to fulfill the goals of phytoextraction. Because different elements have different value in the market some can be phytomined for profit and others can be phytoremediated at lower cost (with associated biomass power generation) than soil removal and replacement. Ni phytoextraction from contaminated or mineralized soils offered economic return greater than producing most crop plants, especially when considering the low fertility or phytotoxicity of Ni rich soils. Only soils that require remediation based on risk assessment will comprise the market for phytoremediation. Improved risk assessment has indicated that most Zn+Cd contaminated soils will not require Cd phytoextraction because the Zn limits practical risk from soil Cd. But rice and tobacco, and foods grown on soils with Cd contamination without corresponding 100-fold greater Zn contamination, allow Cd to readily enter food plants and diets. Clear evidence of human renal tubular dysfunction from soil Cd has only been obtained for subsistence rice farm families in Asia. Because of historic metal mining and smelting, Zn+Cd contaminated rice soils have been found in Japan, China, Korea, Vietnam and Thailand. Phytoextraction using southern France populations of Thlaspi caerulescens appears to be the only practical method to alleviate Cd risk without soil removal and replacement. The southern France plants accumulate 10-20-fold higher Cd in shoots than most Thlaspi populations such as those from Belgium and the UK. Addition of fertilizers to maximize yield does not reduce Cd concentration in shoots; and soil management promotes annual Cd removal. The value of Cd in the plants is low, so the remediation service must pay the costs of Cd phytoextraction plus profits to the parties who conduct phytoextraction. Some other plants have been studied for Cd phytoextraction, but annual removals are lower than the best Thlaspi. Improved Thlaspi cultivars with higher yields and retaining this remarkable Cd phytoextraction potential are being bred using normal plant breeding techniques.