Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/1997
Publication Date: N/A
Interpretive Summary: Heavy metal (Pb, Zn, Cd, Cu, Cr and Ni) contamination of soils poses serious problems to both human health and agriculture in the U.S. Current engineering-based technologies used to remediate soils (e.g., removal of top soil for storage in landfills) are quite costly, and often dramatically ydisturb the landscape. Recently, there has been considerable interest focused on the use of terrestrial plants to absorb heavy metals from the soil and concentrate them in the easily harvestable shoot tissues as an alternative remediation technology. However, little is currently understood about the traits that would make certain plant species the best candidates for phytoremediation of contaminated soils. In this study, we developed a plant growth solution that had the same mineral content as the solution obtained from soil from a site contaminated with high levels of Zn, Cd and Cu. We then screened a number of different plant species and cultivars for their ability to grow on this nutrient solution containing toxic levels of Zn, Cd and Cu, as well as for their ability to accumulate the metals in the shoots. We identified several members of the mustard family that showed promise from this study, and then grew them on pots containing the contaminated soil in the greenhouse. We found that the best candidates for phytoremediation of this site were plant species that were fairly tolerant of the toxic soil conditions and produced reasonable shoot biomass, and also exhibited the ability to accumulate moderate amounts of these metals in the shoots. It is predicted that the use of the best performing plant species from this study would facilitate the remediation of this particular site within 10-15 years.
Technical Abstract: In order to identify populations with the ability to accumulate heavy metals, approximately 300 accessions pertaining to 30 plant species were grown for four weeks in a hydroponic media that approximated the nutrient and heavy metal composition of a soil contaminated with moderate levels of cadmium (Cd), copper (Cu) and zinc (Zn). The results indicated that severa Brassica species exhibited moderately enhanced Zn and Cd accumulation. Selected accessions of Brassica juncea (L.) Czern, B. napus L., and B. rapa L. were then grown in pots with heavy metal-contaminated soil to compare the Zn and Cd phytoextraction by these species to that of Thlaspi caerulescens J. & C. Presl, a known Zn and Cd hyperaccumulator, and two grass species, Agrostis capillaris L. and Festuca rubra L. The three Brassica species were the most effective in removing Zn from the contaminated soil, primarily because they produced more than ten times the shoot biomass produced by T. caerulescens. When the soil was amended with Gro-Power, a commercial soil amendment that improves soil structure and fertility, removal of Zn by plant shoots doubled to more than 30,000 mg Zn pot-1 (4.5 kg). The results suggest that for phytoremediation of metal polluted soils to be successful, a strategy should be considered that combines rapid screening of plant species possessing the ability to tolerate and accumulate heavy metals with agronomic practices that enhance shoot biomass production and/or increase metal bioavailability in the rhizosphere.