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|Title:||2,4,6-Trinitrotoluene (TNT) transformation/sorption in thin-disk soil columns|
|Authors:||North Carolina State University.|
Louisiana State University (Baton Rouge, La.)
Installation Restoration Research Program (U.S.)
Townsend, Daniel M.
Myers, Tommy E.
Adrian, Donald D.
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: Remediation and containment efforts are underway for 2,4,6-trinitrotoluene (TNT) contamination in the subsurface at many Army installations. Contaminant transport modeling, a time and cost-effective tool for comparing various remediation alternatives, is hampered by lack of information on the significance of TNT transformation and sorption in soils. This study was conducted to estimate TNT transformation and sorption parameters from breakthrough curves (BTCS) for three major soil classes -- sand, silt, and clay. An additional objective was to determine if soil transformation of TNT is an exhaustible process. Thin-disk soil columns (0.32-cm soil length) were used to obtain TNT BTCS. Effluent TNT and TNT transformation product concentrations were analyzed as a function of pore volumes eluted. The thin-disk columns produced symmetrical TNT BTCS for each soil. The BTCS were modeled assuming complete-mix, first-order transforrnation, and linear equilibrium sorption. This model produced excellent curve fits, with only slight discrepancies occurring near the beginning and end of the BTCS. Excellent mole balances were observed for each soil. Over 99 percent of the input TNT could be accounted for either as TNT in the effluent, transformed TNT in the effluent, or residual TNT rernaining in the soil columns at the end of the breakthrough experiments. First-order transformation rate constants and linear equilibrium distribution coefficients were estimated from fitted BTCS for each soil. TNT transformation rate constants ranged from 0.008 to 0.025 hr⁻¹, and TNT distribution coefficients ranged from 1.S to 10.0 l/kg. Silt showed the greatest tendency for transformation, and clay showed the greatest tendency for sorption. TNT transformation products were primarily reduction products resulting from transformation of nitro groups to amino groups. Reduction at the 4-carbon position was favored over reduction at the 2- or 6-carbon position. None of the TNT BTCS showed evidence of an exhaustible soil constituent responsible for TNT transformation, suggesting that the observed transformations were primarily biotic, or at least biologically medicated.
|Appears in Collections:||Technical Report|