Aerobic biodegradation potential of subsurface microorganisms from a jet fuel-contaminated aquifer

In 1975, a leak of 83,000 gallons (314,189 liters) of jet fuel (JP-4) contaminated a shallow water-table aquifer near North Charleston, S.C. Laboratory experiments were conducted with contaminated sediments to assess the aerobic biodegradation potential of the in situ microbial community. Sediments were incubated with ¹⁴C-labeled organic compounds, and the evolution of ¹⁴CO₂ was measured over time. Gas chromatographic analyses were used to monitor CO₂ production and O₂ consumption under aerobic conditions. Results indicated that the microbes from contaminated sediments remained active despite the potentially toxic effects of JP-4. ¹⁴CO₂ was measured from [¹⁴C]glucose respiration in unamended and nitrate-amended samples after 1 day of incubation. Total [¹⁴C]glucose metabolism was greater in 1 mM nitrate-amended than in unamended samples because of increased cellular incorporation of ¹⁴C label. [¹⁴C]benzene and [¹⁴C]toluene were not significantly respired after 3 months of incubation. With the addition of 1 mM NO₃, CO₂ production measured by gas chromatographic analysis increased linearly during 2 months of incubation at a rate of 0.099 μmol g^-1 (dry weight) day^-1 while oxygen concentration decreased at a rate of 0.124 μmol g^-1 (dry weight) day^-1. With no added nitrate, CO₂ production was not different from that in metabolically inhibited control vials. From the examination of selected components of JP-4, the n-alkane hexane appeared to be degraded as opposed to the branched alkanes of similar molecular weight. The results suggest that the in situ microbial community is active despite the JP-4 jet fuel contamination and that biodegradation may be compound specific. Also, the community is strongly nitrogen limited, and nitrogen additions may be required to significantly enhance hydrocarbon biodegradation.