Influence of Biogenically Produced Fe(II) and Humic Acid Analogs on the Fate of 2,4,6-Trinitrotoluene (TNT)
Abstract
Pollution of soil and groundwater with explosives, such as TNT, is a well-known environmental problem. Obviously, a precise risk assessment and evaluation of appropriate remediation strategies of TNT require a fundamental understanding of the processes that govern the transformation of TNT in the subsurface. Recently a number of novel Gram positive metal-reducing bacteria were isolated from enrichments of subsurface soils from Cr(VI) contaminated and uncontaminated zones at the US Department of Energy's Hanford site. In contrast to most known metal-reducing bacteria such as Geobacter spp. and Shewanella spp. the isolates were predominantly Gram-positive and 16S rDNA and phospholipid analysis indicated that the isolates predominantly belonged to commonly observed soil bacteria of the genus Cellulomonas. These isolates proved to be capable of Cr(VI), U(VI), dissolved Fe(III), goethite, maghemite, magnetite, hematite, and hydrous ferric oxide (HFO) reduction. Reduced solid phase iron can mediate the degradation of nitroaromatics, halogenated solvents, azo compounds, arsenate, and other important contaminants. Consequently, batch experiments were conducted with Fe(III) minerals (namely, HFO and Magnetite) to investigate the impact of biogenically produced Fe(II) on the fate of TNT. The humic acid analog anthraquinone-2,6-disulfonate (AQDS), can be reduced by Cellulomonas spp. and was included in these studies because of its ability to function as an electron shuttle between the Fe(III) minerals and the bacterial cell during microbial iron reduction. The work to be presented systematically investigates how different factors control the rate and extent of TNT reduction reactions as well as the mechanisms involved. Anaerobic batch studies show the fastest and most complete reduction of TNT in the presence of HFO and the humic analog AQDS. However, we also observe TNT removal by Cellulomonas in the absence of HFO and AQDS with similar TNT reduction rates but with the accumulation of less reduced and polymerized metabolites as analyzed by RP-HPLC with diode array detection. Autoclaved and non-inoculated samples show no significant transformation of TNT. The results suggest that the addition of AQDS (and thus potentially humic substances) can significantly improve the rate and extent of TNT reduction in iron reducing soil environments. A metabolic pathway map elucidating all the metabolites formed and the underlying mechanisms during the degradation of TNT by the Cellulomonas isolates is being established and will become a powerful tool in understanding the biogeochemical fate of TNT in soil environments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.B22E..11B
- Keywords:
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- 0400 BIOGEOSCIENCES;
- 4857 Pollution