A microcosm study was performed to investigate the biodegradation potential of BTX compounds in unsaturated soils under aerobic and anaerobic conditions. Toluene was used as a model compound at concentrations of 100 to 200 mg/L. An uncontaminated, groseclose soil ranging in depth from 0 to 18 feet was used in order to observe differences in microbial degradation abilities in shallow subsurface environments. Several metabolic groups were investigated including aerobes, denitrifyers and sulfate reducers. Bacterial densities of these groups were determined at each soil depth. Physical and chemical parameters of the subsurface environments were also investigated to observe their impact on microbial biodegradation potentials. These included changes in soil particle size, moisture content, and pH with increasing depth. Substantial toluene biodegradation took place in some, but not all soils under both aerobic and denitrifying conditions. Biodegradation rates varied considerably among aerobes and denitrifyers in similar environments. In acidic, poorly drained clay soils of 3, 6 and 9 feet, denitrifyers readily degraded toluene while aerobic microorganisms were unable to mineralize the compcund. Evidence of toluene biodegradation by anaerobic bacteria including sulfate reducers was also observed in moist, clay soils although the rates were much slower. Currently, in situ bioremediation techniques for benzene, toluene and xylene compounds almost always rely on indigenous, aerobic organisms to degrade the contaminants. However, results of this study indicate that aerobic organisms capable of biodegradation may not exist in some subsurface environments, even in soils very close to the surface. The physical/chemical properties of unsaturated environments have significant impacts on microbial capabilities as well as the biodegradation potential of contaminants. / Master of Science

Master of Science

Indiana University-Purdue University Indianapolis (IUPUI) / Organic-rich substrates such as soil provide an excellent carbon source for bacteria. However, hydrocarbons such as those found in various ignitable liquids can also serve as a source of carbon to support bacterial growth. This is problematic for fire debris analysis as samples may be stored at room temperature for extended periods before they are analyzed due to case backlog. As a result, selective loss of key components due to bacterial metabolism can make identifying and classifying ignitable liquid residues by their chemical composition and boiling point range very difficult. The ultimate goal of this project is to preserve ignitable liquid residues against microbial degradation as efficiently and quickly as possible. Field and laboratory studies were conducted to monitor microbial degradation of gasoline and other ignitable liquids in soil samples. In addition to monitoring degradation in potting soil, as a worst case scenario, the effect of soil type and season were also studied. The effect of microbial action was also compared to the effect of weathering by evaporation (under nitrogen in the laboratory and by the passive headspace analysis of the glass fragments from the incendiary devices in the field studies). All studies showed that microbial degradation resulted in the significant loss of n-alkanes and lesser substituted alkylbenzenes predominantly and quickly, while more highly substituted alkanes and aromatics were not significantly affected. Additionally, the residential soil during the fall season showed the most significant loss of these compounds over the course of 30 days. To combat this problem, a chemical solution is to be immediately applied to the samples as they are collected. Various household and commercial products were tested for their efficacy at low concentrations to eliminate all living bacteria in the soil. Triclosan (2% (w/v) in NaOH) proved to be the most effective at preserving ignitable liquid residues for at least 30 days.