Bioaugmentation of TNT-contaminated soil

Abstract

Microbial transformation of trinitrotoluene (TNT) in phics. contaminated soil was investigated in this research. A Bacillus sp., isolated from soil obtained from an army ammunition facility, was used to enhance the rate of TNT removal over a 360 day test period. The soil treatments in this study included: (1) the Bacillus sp., (2) the existing indigenous microorganisms, and (3) a sterile control. The disappearance of TNT, as measured by high performance liquid chromatography (HPLC), was compared to the reduction in mutagenic activity of hexane:acetone solvent extracts, as measured in the Salmonella/microsome assay with the histidine requiring TA98 tester strain. The results indicated a similar TNT removal rate in all three treatments. The TNT in the microbial treatments started at approximately 47[]13 mg g[] soil. By day 360, this concentration was reduced to 28[]10 mg g soil in the Bacillus sp the indigenous microbial treatment. The sterile control treatment and 26[]8 mg g[] which was reduced to 22[]2 started with a day 0 TNT concentration of 31[]6 mg g [] day 360. This represented a disappearance of between 30-40% of the g [] y original TNT in all three treatments. The reduction in mutagenicity, as indicated by weighted activity calculations, differed between the microbial treatments and the sterile control. A 50-60% reduction was observed in the microbial treatments. In the boxes treated with the addition of the Bacillus sp. the weighted activity at a dose of 16 :g/plate started at 49[]13 net revenants per microgram solvent extract on microgram after 360 days. The solvent extracts from soil treated with indigenous microorganisms went from a weighted activity of 47[]15 net revenants per microgram on day 0 to 17[]5 on day 360. The sterile control did not reduce mutagenicity by any appreciable amount. The day 0 weighted activity was measured to be 44[]11 net revenants per microgram solvent extract and on day 360 it was 50[]1 . The TNT concentrations in the sterile control samples were lowest throughout the study however, the mutagenicity was highest.