Grantee Research Project Results
Final Report: Transgenic Citrate-Producing Plants for Lead Phytoremediation
EPA Contract Number: 68D02018Title: Transgenic Citrate-Producing Plants for Lead Phytoremediation
Investigators: Elless, Mark P.
Small Business: Edenspace Systems Corporation
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2002 through September 1, 2002
Project Amount: $69,660
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: SBIR - Waste , Hazardous Waste/Remediation , Small Business Innovation Research (SBIR)
Description:
In 1991, the U.S. Secretary of Health and Human Services identified lead as "the number one environmental threat to the health of children in the United States." Lead exposure can cause premature birth and impair a child's mental and physical development. In adults, lead exposure can cause kidney damage, high blood pressure, and other problems. The U.S. Environmental Protection Agency estimates that 12,000,000 homes exceed the new 400 mg/kg standard for soil lead in play areas. Soil lead at small arms firing ranges, manufacturing plants, and other government and industrial sites poses similar challenges.
A promising alternative to excavation and replacement of lead-contaminated soil is phytoremediation, whereby living plants remove lead from the soil at firing ranges, industrial sites, and residences. Phytoremediation relies on crop species and chelators that facilitate higher plant uptake rates. The annual cost of chelators can be as high as $20,000 per acre. Furthermore, sites with sandy, well-drained soil may need a water-impermeable liner to prevent slowly degrading chelators such as ethylenediamine tetraacetic acid from leaching metals into groundwater. Costs of a liner can double the total cost of phytoextraction, rendering phytoremediation impractical for certain sites.
The goal of this Phase I research project was to measure the performance of transgenic and nontransgenic tobacco strains to extract lead via root exudation of a rapidly biodegradable chelator-citric acid-using two contaminated soils (lead-spiked soil, actual lead-contaminated soil) and one uncontaminated control soil. Successful demonstration of this technology could enable a cost savings of more than 70 percent in lead phytoextraction compared to traditional chelate application.
Summary/Accomplishments (Outputs/Outcomes):
A citrate synthase (CS) transgene was placed under the control of different plant promoters to overexpress the gene in roots. Edenspace Systems Corporation created and tested 100 lines of CS-transgenic tobacco (Nicotiana tabacum). Preliminary results with five hemizygous strains are promising, suggesting that higher performing homozygous strains created at the end of Phase I may hyperaccumulate lead from soil (bioconcentration factor > 1). Significantly, little soluble lead remained in the soil, indicating that the plants may successfully address leaching concerns.
Specifically, the following observations may be made about the data obtained in this study:
· Comparison of lead uptake in transgenic tobacco plants grown in lead-spiked soil versus an actual lead-contaminated soil showed that most of the transgenic lines outperformed the control in the actual lead-contaminated soil, whereas in the spiked soil, the performance of the control was comparable to that of the transgenic lines. This result is consistent with the possibility that the performance advantage of additional root citrate is greater for site soils in which lead bioavailability is low. When lead bioavailability is high, as in a spiked soil, the performance advantage may decrease or disappear.
· Edenspace's foliar amendment successfully increased uptake of lead in transgenic plants as well as in nontransgenic plants. The increase was an average of 121 percent, with the greatest increase in the U2 and control lines (159 and 202 percent, respectively).
· Application of 20 mmol/kg of citric acid to the soil prior to harvest, a standard Edenspace phytoremediation treatment, induces substantially more lead uptake than is observed in the transgenic plants. However, because of the substantial expense of such soil amendments, the cost/benefit tradeoff of their use is likely to be site-specific.
· The data suggest that substantial amounts of lead may be accumulated even by nontransgenic tobacco plants grown in lead-contaminated soils. Edenspace has not found this result in the literature, and it may not be widely known. Commercial growers of tobacco should, therefore, use caution when planting in locations such as old firing ranges or battlefields where elevated soil lead levels may be encountered.
Conclusions:
Transgenic tobacco plants that exude citric acid from their roots directly into the rhizosphere were shown to accumulate lead and uranium from contaminated soils in an environmentally protective manner. These successful findings are the basis for a Phase II project, in which Edenspace proposes the use of higher performance transgenic tobacco strains to accelerate the phytoextraction of lead from contaminated soils in both growth chamber studies and two field demonstrations (at a small arms firing range in Maryland and a residential site in Massachusetts). Phase II objectives also include concentrating lead in harvested plants to facilitate disposal or recycling, and creating transgenic lines of a proven lead-accumulating plant species, Brassica juncea.
Supplemental Keywords:
phytoextraction, phytoremediation, tobacco, Nicotiana tabacum, Brassica juncea, lead, metals, groundwater, ethylenediamine tetraacetic acid, EDTA, chelator, transgenic plants, root exudates, contaminant, soil, small business, SBIR., RFA, Scientific Discipline, Health, Waste, Contaminated Sediments, Remediation, Chemistry, Microbiology, Environmental Microbiology, Risk Assessments, Hazardous Waste, Molecular Biology/Genetics, Bioremediation, Children's Health, Biology, Environmental Engineering, Hazardous, degradation, petroleum contaminants, biodegradation, lead, cleanup, decontamination of soil, children, soils, childhood lead exposure, contaminated soil, contaminants in soil, bioremediation of soils, soil, human exposure, models, citrate producing plants, hydrocarbons, children's environmental health, lead exposure, phytoremediationSBIR Phase II:
Transgenic Citrate-Producing Plants for Lead Phytoremediation | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.