Transgenic Citrate-Producing Plants for Lead Phytoremediation

In 1991, the Secretary of the U.S. Department of Health and Human Services called lead "the number one environmental threat to the health of children in the United States." Lead poisoning affects 890,000 U.S. children between the ages of 1 and 5, causing aggressive behavior, hyperactivity, and learning problems. In adults, increased lead levels have been linked to kidney problems, high blood pressure, damaged hearing, blindness, brain damage, and mental retardation. A major source of lead exposure is dust stirred up in sites contaminated by lead paint, leaded gasoline, or lead from mining or industrial activities. This widespread problem affects an estimated 18 percent of U.S. homes. A promising alternative to excavation and replacement of soil is extraction of lead using living plants. Lead phytoremediation relies on the use of crop species, including turf grasses, with a combination of chelating agents and other amendments that induce enhanced plant availability of the contaminant and higher plant uptake rates. The cost of such amendments can range up to $20,000 per acre per growing season. Furthermore, sites with sandy, well-drained soil over shallow groundwater may need to use a water-impermeable liner to prevent slowly degrading chelating agents such as ethylenediamine tetraacetic acid (EDTA) from leaching metals into groundwater. Costs associated with installing and maintaining a liner can more than double the total cost of phytoextraction, and the need for a liner may render phytoremediation impractical for many sites.