| Abstract
| - The distribution of TNT* (the sum of TNT and its degradationproducts), aniline, and nitrobenzene between particulateorganic matter (POM), dissolved soil organic matter (DOM),and free compound was studied in controlled kinetic(with and without irradiation) and equilibrium experimentswith mixtures of POM and DOM reflecting naturalsituations in organic rich soils. The binding of TNT* toPOM was fast, independent of irradiation, and adsorptionisotherms had a great linear contribution (as determinedby a mixed model), indicative of a hydrophobic partitioningmechanism. The binding of TNT* to DOM was slower,strongly enhanced under nonirradiated conditions, andadsorption isotherms were highly nonlinear, indicative ofa specific interaction between TNT derivatives and functionalgroups of DOM. Nitrobenzene was associated to bothPOM and DOM via hydrophobic partitioning, whereas anilinebinding was dominated by specific binding to POM andDOM functional groups. On the basis of nitrobenzene andTNT* adsorption parameters determined by a mixedLangmuir + linear model, POM had 2−3 times greaterdensity of hydrophobic moieties as compared to DOM. Thisdifference was reflected by a greater (O + N)/C atomicratio for DOM. The sum of C−C and C−H moieties, asdetermined by X-ray photoelectron spectroscopy (XPS), andthe sum of aryl−C and alkyl−C, as determined by solid-state cross-polarization magic-angle spinning (CP-MAS) 13CNMR, could only qualitatively account for differences inadsorption parameters. Aliphatic C was found to be moreimportant for the hydrophobic partitioning than aromaticC. On the basis of nonlinear adsorption parameters, the densityof functional groups reactive with aniline and TNTderivatives was 1.3−1.4 times greater in DOM than inPOM, which was in fair agreement with 13C NMR and XPSdata for the sum of carboxyl and carbonyl groups aspotential sites for electrostatic and covalent bonding. Weconclude that in contaminated soils characterized bycontinuous leaching of DOM, formation of TNT derivatives(via biotic and abiotic reductive degradation) and theirpreference for specific functional groups in DOM maycontribute to a significant transportation of potentially toxicTNT compounds into surface waters and groundwaters.
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