In this study, soil collected from locations under three different uses (residential, agricultural, brownfield) were spiked with gasoline, and microbial degradation was monitored for 30 days; the soils were also chemically and biologically characterized.
During the investigation of a suspicious fire, debris is often collected from the scene and analyzed for residues of ignitable liquids (e.g., gasoline). In cases where the debris is contaminated with soil, it is known that heterotrophic soil microorganisms can alter the chemical composition of the ignitable liquid residue over time; however, the effects of soil type and season upon this phenomenon are not known. In the current study, gas chromatographic profiles showed that residential soil was most active and brownfield soil least active for the microbial degradation of gasoline. The brownfield soil possessed relatively high (497 mg/kg) concentrations of Pb, which may have affected bacterial activity. Predominant viable bacterial populations enumerated using real-time reverse transcriptase polymerase chain reaction (RT-PCR) included members of the Alcaligenes, Acinetobacter, Arthrobacter, Bacillus, Flavobacterium, and Pseudomonas genera. Principal Components Analysis (PCA) was found to be effective in revealing trends of microbial degradation among the different soil types and seasons. The results of this study demonstrate the necessity of prompt analysis of forensic evidence for proper identification of possible ignitable liquids. (publisher abstract modified)