Bioremediation of Contaminated Soils by Echinacea purpurea and Arbuscular Mycorrhizal Fungi

Abstract

As a potential bioremediation system for contaminated soils, I evaluated the use of an arbuscular mycorrhizal (AM) fungus, Glomus intraradices on roots and shoots uptake of polycyclic aromatic hydrocarbons (PAHs), alkyl PAHs, and toxic metals in Echinacea purpurea, in using a controlled 20-week greenhouse study and a complimentary 2-year field study. E. purpurea seeds were either inoculated with the mycorrhizal fungus (AM) or not inoculated (non-AM) and grown in soil provided by the National Capital Commission (NCC) that have known contamination. In the greenhouse study, AM inoculation increased the uptake of alkyl PAHs in the roots of E. purpurea. The AM inoculation showed no effect on root uptake of PAHs and toxic metals over the 20-week study period. However, when I calculated the uptake rates (k1) for PAHs between both treatments, the AM treated roots ha 10-fold higher k1 values than non-AM treated roots. The soil concentrations of PAHs were found to increase over time with AM inoculation, suggesting, that AM fungi are causing a solvent depletion through root uptake of minerals and carbon, which concentrates the more hydrophobic PAHs in soils. Alkyl PAHs and metals showed no change over time amongst any of the treatments. Assessing the performance of AM fungi on the uptake of contaminants under field conditions, only PAHs showed increased bioaccumulation in the shoots of E. purpurea with AM inoculation. Alkyl PAHs and metals in plant material were unaffected by the AM inoculation, but increased significantly from year 1 to year 2. The uptake rates among treatments were similar, with non-AM roots having slightly greater uptake. Soil concentrations of PAHs and alkyl PAHs were unaffected over the course of the experiment. Our control soil, however, showed significant increases in concentration from year 1 to year 2 with alkyl PAHs. These results quantified the influence of AM hyphae-mediated uptake of organic and inorganic contaminant transfer from soil to plants and the bioaccumulation kinetics for contaminants by E. purpurea that will be useful for environmental models and phytoremediation strategies.