Characterization of ¹⁵N-TNT Residues After an Anaerobic/Aerobic Treatment of Soil/Molasses Mixtures by Solid-State ¹⁵N NMR Spectroscopy. 2. Systematic Investigation of Whole Soil and Different Humic Fractions

Abstract

An anaerobic/aerobic composting experiment with 15N-2,4,6-trinitrotoluene (TNT) spiked soil was performed to investigate the fate of the explosive under the applied conditions. For a qualitative description of TNT-residues formed during the composting process, bulk soil and different soil fractions were subjected to solid-state 15N NMR spectroscopy. Major resonance signals could be detected in the chemical shift regions of five-ring heterocyclic nitrogen and in the area of aniline derivatives and primary amines. Distinct nitro peaks were found in the bulk samples and in the humic fractions obtained with a mild extraction procedure. This signal disappeared in the material extracted with a more drastic procedure. Quantitative investigations of the 15N distribution in the composted material revealed that 33% of the stable nitrogen isotope was incorporated into the humic- and fulvic acid, and 23% was present in the humin. Furthermore 38.8% of the 15N present in the composted material could be allotted to condensed TNT residues, whereas 1.9% are assigned to nitro functions and 15.2% to amino functions. In the investigation presented here a bioremediation method was simulated with 15N-TNT spiked soil. The nonradioactive label allowed a qualitative and quantitative characterization of residues of the explosive. Our results give strong evidence for a stable incorporation of the nitroaromatics into the humic material of soils. However, further investigations will be necessary to prove a long-time stability of bound TNT residues and to assess toxicological effects of the treated soil.