Submitted to: Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/31/2007
Publication Date: 2/13/2008
Citation: Smith, D.J., Craig, A.M., Duringer, J.M., Chaney, R.L. 2008. Absorption, tissue distribution, and elimination of residues after 2,4,6-trinitro[14C]toluene administration to sheep. Environmental Science and Technology 42(7):2563-2569. Interpretive Summary: 2,4,6-Trinitrotoluene (TNT) is an explosive compound that was produced and used for military and industrial purposes for over 100 years in the United States. Because of its relative stability and safety TNT was widely used, but is now considered a major contaminate of both industrial and military sites. Estimates suggest that over 1 million tons of soils are contaminated with TNT residues. Contamination of soils with TNT is of concern because of its potential to leach into water systems and because TNT and some of its metabolites are considered mutagens and possible carcinogens. Remediation efforts are currently underway at some of the most contaminated sites but at great financial costs. Previous studies have shown that TNT is very rapidly metabolized by gastrointestinal fluids from grazing animals such as cattle. It was believed that TNT was detoxified by the ruminant gastrointestinal fluid. This study was conducted to determine the fate of TNT in live sheep. Sheep were dosed with low levels of TNT and blood, urine, feces, and tissues were collected. We learned that sheep rapidly detoxify TNT to residues that are bound to organic molecules and that most of the bound residues are excreted in the fecal matter of sheep. The use of grazing animals on ground with low levels of TNT contamination has the potential to speed the reclamation of these lands at fairly low cost.
Technical Abstract: 2,4,6-Trinitrotoluene (TNT) is a persistent contaminant present in high concentrations of some industrial and military sites. Traditional biological bioremediation techniques typically rely on the immobilization of TNT reduction products rather than on TNT mineralization. We hypothesized that sheep ruminal microbes would be suitable for TNT destruction after phytoremediation of TNT-contaminated soils by cool-season grasses. The purpose of this study was to determine the fate of 14C-TNT in ruminating sheep in an initial effort to determine the utility of ruminant animals as a portion of the bioremediation process. Three wether sheep were dosed with 35.5 mg each of dietary unlabelled TNT for 21 consecutive d. On d 22 sheep (41.9 +/- 3.0 kg) were orally dosed with 35.5 mg of U-ring labeled [14C]TNT (129 micro curie; 99.1% radiochemical purity). Blood was serially collected, and urine and feces were collected at regular intervals for 72 hours. At slaughter, tissues were quantitatively collected. Tissues and blood were analyzed for total radioactive residues; excreta were analyzed for total radioactive residues, bound residues, and TNT metabolites. Plasma radioactivity peaked within 1 h of dosing and was essentially depleted within 18 h. Approximately 76% of the radiocarbon was excreted in feces, 17% in urine, with 5% being retained in the gastrointestinal tract and 1% retained in tissues. Parent TNT, dinitroamino metabolites, and diaminonitro metabolites were not detected in excreta. Ruminal and fecal radioactivity was essentially non-extractable using ethyl acetate, acetone, and methanol; covalent binding of fecal radioactive residues was evenly distributed among extractable organic molecules (i.e., soluble organic matter, soluble carbohydrate, protein, lipid and nucleic acid fractions) and undigested fibers (cellulose, hemicellulose, and lignin). This study demonstrated that TNT reduction within the ruminant gastrointestinal tract leads to almost complete immobilization of residues to organic matter, a fate similar to TNT in other strongly reducing environments.