UTILIZING 13C-LABELED SUBSTRATES TO ASSESS MICROBIAL DEGRADATION OF POLYCYCLIC AROMATIC HYDROCARBONS THROUGH COMPOUND SPECIFIC ISOTOPE ANALYSIS OF PHOSPHOLIPID FATTY ACIDS

Phospholipid fatty acids (PLFAs) are major membrane components in all living cells that are degraded within days of cell death. PLFAs isolated from soils are derived solely from active microbial communities. Carbon is directly incorporated into these compounds from various substrates, such as chlorinated solvents, aliphatic compounds, and polycyclic aromatic hydrocarbons (PAHs). Microcosm experiments with chlorinated solvents have shown the isotopic compositions of individual PLFAs reflect incorporation of enriched carbon from these 13C-labeled compounds. These isotope values are direct evidence of degradation.

Soils samples were recovered from the Tennessee Products industrial site located in Chattanooga, TN. The site was occupied by a former coal coking plant where large amounts of coal tar and creosote were discharged onto the site. The soils, surface, and groundwaters are extensively contaminated with PAHs. Naphthalene levels of up to 15 ppm have been detected and concentrations of phenanthrene and fluoranthene range from 3 to 5 ppm. The presence of degradation intermediates such as 9-fluorenol and alkylated PAHs suggest active degradation is occurring at this site and the soils at Chattanooga Creek are suitable for natural attenuation of PAHs.

The focus of this research is to identify which microbial communities are capable of degrading PAHs under aerobic conditions. Several microcosm experiments utilizing13C-labeled PAHs are currently underway to determine degradation rates and identify the communities responsible for degradation under controlled conditions representative of the Chattanooga Creek site.