Chemically Induced Phytoextraction of Lead (Pb) Contaminated Soil by Switchgrass (Panicum virgatum L.)
Soils contaminated with lead (Pb) from human activities including industrial byproducts create an environmental and human health risk. Phytoextraction through chemical acquisition of Pb in soils offer a potentially cost effective and ecologically driven approach to remediation. Switchgrass (Panicum virgatum L.) is known to have a tolerance for a wide range of heavy metals including Pb. Switchgrass is also able to grow in a wide range of climates. Soil chemistry manipulation, using chelates and plant growth promoters could provide an effective field method for phytoremediation using switchgrass. In this study chemically enhanced phytoextraction using the soil-fungicide Infuse (active ingredient propiconazole), the chelator nitrilotriacetic acid (NTA), and the phytohormones salicylic acid (SA) and benzylaminopurine (BAP) were tested on switchgrass grown in Pb contaminated soil from a former superfund site in Cedartown, GA. The soil chemical manipulation aimed at increasing the bioavailability and uptake of Pb by switchgrass. Previously, the chelate ethylenediaminetetraacetic acid (EDTA) was found to be effective in increasing the bioavailability of Pb in soils but the main problem with its use was a long persistent time in soils. The chelator NTA is a derivative of EDTA which has been found to persist for a much shorter length of time in soils comparatively and in this study, is tested as an alternative to EDTA. Switchgrass was planted in 5L pots containing Pb-contaminated soil and grown in the Kennesaw State University Research Greenhouse. Pots were given 200 ml of nutrient solution twice a week for six months. On 49 days after planting (dap), foliar application of the phytohormones salicylic acid and benzylaminopurine were sprayed on target plants twice a week. On 170 dap, Infuse solution was given to target plants. On 184 dap, the NTA solution was given to target plants twice a week for a one-month period. The NTA solution was brought to pH 5.5 using citric acid. Increased soil acidity would increase the bioavailability of Pb. The NTA solution was applied alongside the soil fungicide Infuse for suppression of symbiotic arbuscular mycorrhizal fungi with the aim of increasing Pb uptake. On 226 dap, plants were harvested. Acid digested plant samples were analyzed for Pb using an ICP-OES instrument at the Chemistry Department of Kennesaw State University. Soil application of NTA and Infuse significantly increases the concentration of Pb in the foliage of plants in all treatments over Control plants and the standard Infuse treatment. Application of the soil fungicide Infuse containing resulted in a significantly higher concentration of Pb in plants foliage compared to Control plants. The difference in Pb concentration of plants foliage among plants in different NTA treatments was insignificant but the highest average Pb concentration was found in the NTA treatment without foliar phytohormone application. This suggests that the phytohormones SA and BAP could play a role in a resistance to heavy metal toxicity. Biomass increases were insignificant between all treatments. This indicated that under the NTA application, the phytohormones did not have a great effect on biomass among treatments. The NTA application demonstrated that using this chelator will significantly increase translocation and concentration of the heavy metal Pb in switchgrass above ground biomass. The application of NTA alongside the soil fungicide Infuse can provide the tools for a viable technique for phytoremediation of Pb contaminated soils without potentially harmful effects of long-term persistence.
Switchgrass, Panicum virgatum, Phytoextraction, Nitrilotriacetic acid, Lead, Second generation bioenergy crop, Biology, Environmental Health, Integrative Biology, Other Pharmacology, Toxicology and Environmental Health
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