Energy Crops for Reducing Areawide Lead Soil Contamination

Because areawide lead soil contamination poses significant risks to large populations in the United States, reducing lead levels in these soils is an important environmental health priority. Current methods that address localized, small-scale lead contamination, such as excavation and replacement of soil, are too expensive for large-scale application. This Phase I SBIR project seeks to develop an innovative, low-cost method of extracting lead from soils over wide areas using phytoextraction with transient phytoextraction agents (TPAs) and high-biomass grasses suitable for energy production. TPAs are chelants such as citric acid that induce lead uptake into plants from soil and that biodegrade more rapidly than ethylenediaminetetraacetic acid (EDTA), thereby decreasing the risk of off-site migration of chelated lead. The use of TPAs with turf grass to safely remediate soil lead at urban residences recently has been demonstrated. This project will evaluate switchgrass and elephant grass, two high-biomass plants targeted for production of power and cellulosic ethanol and for their ability to accumulate lead following TPA application to lead-contaminated soils collected from sites contaminated by smelters and mining. Mobility of the lead remaining in each soil after treatment will be assessed by sequential extraction to determine changes, if any, in post-treatment soil lead bioavailability due to TPA application. Because disposal of large amounts of contaminated plant biomass is a significant challenge for areawide phytoremediation of lead, in Phase I the harvested biomass will be processed to estimate costs and benefits of: (1) co-firing lead-contaminated biomass in a coal power plant, or (2) producing cellulosic ethanol from the biomass and recycling or disposing of the recovered lead. Following achievement of the Phase I objectives, Phase II will explore methods of increasing process efficiency and decreasing costs, concluding with a field demonstration. The end result of the project will be to establish the foundation for a low-cost, solar-powered method of removing lead over large areas of soil that also produces useful renewable energy co-products.