Hydrophobicity, toxicity and lability of PAH-contaminated soil undergoing phytoremediation
Abstract
Phytoremediation has been shown to be a viable technology for remediation of contaminated soils. This study evaluated the impact of phytoremediation, bioremediation (unplanted-fertilized control) and natural attenuation (unplanted-unfertilized control) on soil from a manufactured gas plant contaminated with recalcitrant polycyclic aromatic hydrocarbons. Two greenhouse studies investigated the potential transport, dissipation and plant translocation of the 16 EPA priority pollutants by fescue (Festuca arundinacea), switchgrass ( Panicum virgatum) and zucchini (Curcubita pepo Raven). The greatest reduction in degradation was observed for planted (fescue and switchgrass) and fertilized treatments corresponding to an overall reduction of 68 and 71% in total PAHs compared to 57% in unplanted-unfertilized treatments following 12 months of treatment. There were no significant differences in plant biomass and microbial numbers between plant species. Although plant biomass PAH concentrations were negligible, root PAH concentrations were shown to correlate well with root biomass. Soil moisture was significantly correlated with all toxicity assays. Reductions in soil hydrophobicity were observed in both planted and unplanted treatments after 12 months with the greatest reduction occurring in unplanted-fertilized and unplanted-unfertilized treatments. Soil water retention increased in switchgrass treatments, which were strongly correlated with predictions of water retention. Zucchini enhanced degradation for 2–3 ring and specific 5-ring PAHs after 90 days of treatment when compared with the unvegetated soil, with an overall degradation of 27%. Rhizosphere microbial numbers increased by 3 orders of magnitude along with a 50% increase in microbial respiration in the presence of zucchini roots. Negligible amounts of PAHs were detected in the plant roots and shoots, with no detectable concentrations in the fruit. Labile contaminant concentrations were shown to strongly correlate with estimates of pore water concentrations. Strong correlations also were noted between labile PAH concentrations and nematode and earthworm bioassays. In this study, phytoremediation was shown to be effective for reduction of contaminant concentrations, soil toxicity and water repellency. Hence, overall goal of phytoremediation should shift from a metric focused primarily on contaminant dissipation to one where reestablishment of a favorable environment for ecosystem sustainability and improved soil quality are key parameters.
Degree
Ph.D.
Advisors
Banks, Purdue University.
Subject Area
Civil engineering|Environmental engineering|Environmental science|Agronomy
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