Denitrification and biodegradation in polycyclic aromatic hydrocarbon contaminated soils

Increasing offsite contamination and toxicity from leaky underground storage tanks (LUST) have prompted research into alternative remediation methods for petroleum-contaminated soil. Since LUST contain polycyclic aromatic hydrocarbons (PAH) mixtures; the different compounds, their interactions, and frequent anaerobiosis of contaminated subsurface environments are challenges to bioremediation. We hypothesized that native subsurface denitrifying bacteria could contribute to LUST remediation under multiple environmental conditions. The study's objectives were to: determine the potential of native subsurface soil microorganisms, specifically denitrifying bacteria for PAH biodegradation in subsurface soil polluted with petroleum mixtures; and to assess effects and interactions of soil properties, petroleum mixture concentrations, and environmental conditions (O{dollar}sb2{dollar} and H{dollar}sb2{dollar}O levels and temperature) on the growth and activity of native microorganisms. Soils (2-3 m depth) were excavated from uncontaminated sites (River sand ("sandy") and Kennebec silt loam ("clayey")) in Kansas to compare textural effects. These materials were incubated with a simulated jet fuel mixture (0, 800, 8,000, and 80,000 {dollar}mu{dollar}g mixture g{dollar}sp{lcub}-1{rcub}{dollar} soil) at 15{dollar}spcirc{dollar}C and 25{dollar}spcirc{dollar}C. Growth and activity of denitrifying bacteria was stimulated with contamination (800 and 8,000 {dollar}mu{dollar}g mixture g{dollar}sp{lcub}-1{rcub}{dollar} soil) in both materials and with changing environmental conditions, especially from aerobic to saturated anaerobic at 25{dollar}spcirc{dollar}C. Water additions produced the greatest activity; this was probably from separation of microorganisms from inhibitory or toxic mixture components. The mixture could have been a C source in the energy-poor sandy material. Activity was inhibited in the clayey material possibly from microsites with higher mixture concentrations from the higher colloidal fraction in the clayey material. We proved these microorganisms degrade multiple PAH ({dollar}sp{lcub}14{rcub}{dollar}C napthalene and {dollar}sp{lcub}14{rcub}{dollar}C phenanthrene) in aerobic and anaerobic conditions in both materials at 8,000 {dollar}mu{dollar}g mixture g{dollar}sp{lcub}-1{rcub}{dollar} soil and 25{dollar}spcirc{dollar}C. However, little PAH changes to {dollar}sp{lcub}14{rcub}{dollar}CO{dollar}sb2{dollar}; most remains in the soil (up to 93%) or is volatilized (up to 59%). Evidence exists for volatile metabolite formation during biodegradation; this could affect later biodegradation options and possible offsite contamination. We showed that native subsurface soil microorganisms, possibly denitrifying bacteria, degrade PAH in a petroleum mixture under multiple environmental conditions, thereby indicating their potential contribution to LUST bioremediation.