Petroleum and Chlorinated Hydrocarbon Analysis in Support of In Vitro Studies of Natural Anaerobic and Aerobic Microbial Degradation of Xenobiotics in Contaminated Groundwater and Soil

This program investigated in situ biological degradation as a remedial treatment technique at a United States Air Force Base in Texas. Soil and groundwater samples from the site were characterized regarding microbial populations and presence or absence of priority pollutant xenobiotics and petroleum hydrocarbon components. Time-series analyses of replicate nutrient-amended microcosms after approximately 1, 25, 50 and 100 days permitted aerobic and anaerobic degradation rate evaluation. Microcosm integrity was demonstrated throughout the experiment by observing appropriate dissolved oxygen, pH, oxidation/reduction potential, and sterile/viable conditions. Gas chromatographic analysis and ratios of straight-chain and isoprenoid components clearly demonstrated that aerobic conditions were preferred for degradation of aliphatic and aromatic petroleum hydrocarbons. Electron capture gas chromatographic analyses and purge-and-trap gas chromatographic/mass spectrometric analyses of lower molecular weight chlorinated species demonstrated that anaerobic conditions were required to promote significant degradation of these components. Some evidence of lower molecular weight chlorinated species generation due to microbial and abiotic processes was also observed.