Microbial Degradation of Gasoline in Soil: Effect of Season of Sampling

In cases where fire debris contains soil, microorganisms can rapidly and irreversibly alter the chemical composition of any ignitable liquid residue that may be present. In this study, differences in microbial degradation due to the season in which the sample is collected was examined. Soil samples were collected from the same site during Fall, Winter, Spring and Summer and the degradation of gasoline was monitored over 30 days. Predominant viable bacterial populations enumerated using real-time PCR and reverse transcriptase polymerase chain reaction (RT-PCR) enumeration revealed the predominant viable bacterial genera to be Alcaligenes, Bacillus, and Flavobacterium. Overall, the compounds most vulnerable to microbial degradation are the n-alkanes, followed by the mono-substituted alkylbenzenes (e.g., toluene, ethylbenzene, propylbenzene and isopropylbenzene). Benzaldehyde (a degradation product of toluene) was also identified as a marker for the extent of biodegradation. Ultimately, it was determined that soil collected during an unusually hot and dry summer exhibited the least degradation with little to no change in gasoline for up to 4 days, readily detectable n-alkanes for up to 7 days and relatively high levels of resilient compounds such as o-xylene, p-xylene and 1,3,5-trimethylbenzene. These results demonstrate, however, that prompt preservation and/or analysis of soil evidence is required in order to properly classify an ignitable liquid residue

Enterotoxin Production in Natural Isolates of Bacillaceae outside the Bacillus cereus Group

Thirty-nine Bacillus strains obtained from a variety of environmental and food sources were screened by PCR for the presence of five gene targets (hblC, hblD, hblA, nheA, and nheB) in two enterotoxin operons (HBL and NHE) traditionally harbored by Bacillus cereus. Seven isolates exhibited a positive signal for at least three of the five possible targets, including Bacillus amyloliquefaciens, B. cereus, Bacillus circulans, Bacillus lentimorbis, Bacillus pasteurii, and Bacillus thuringiensis subsp. kurstaki. PCR amplicons were confirmed by restriction enzyme digest patterns compared to a positive control strain. Enterotoxin gene expression of each strain grown in a model food system (skim milk) was monitored by gene-specific reverse transcription-PCR and confirmed with the Oxoid RPLA and Tecra BDE commercial kits. Lecithinase production was noted on egg yolk-polymyxin B agar for all strains except B. lentimorbis, whereas discontinuous beta hemolysis was exhibited by all seven isolates grown on 5% sheep blood agar plates. The results of this study confirm the presence of enterotoxin genes in natural isolates of Bacillus spp. outside the B. cereus group and the ability of these strains to produce toxins in a model food system under aerated conditions at 32°C

Air stripping of volatile organic chlorocarbons: System development, performance, and lessons learned

The Savannah River Site, which has been in operation since the 1950`s, is a 780-square kilometer reservation that produces tritium for the national defense program. As a result of past waste handling practices, the ground water at several locations on the Site has become contaminated with solvents, metals, and radionuclides. In 1981, the ground water located under the Site`s fuel and target rod fabrication area (M-Area) was found to be contaminated with degreasing solvents, specifically trichloroethylene (TCE) and tetrachloroethylene (PCE). In 1983, a program was started to evaluate air stripping and determine its applicability to cleanup of M-Area contamination. Lessons learned regarding the efficiency and effectiveness of air stripping technology are presented