Characterization of N-15-TNT residues after an anaerobic/aerobic treatmentof soil/molasses mixtures by solid state N-15 NMR spectroscopy. 2. Systematic investigation of whole soil and different humic fractions

An anaerobic/aerobic composting experiment with N-15-2,4,6-trinitrotoluene (TNT) spiked soil was performed to investigate the fate of the explosive un der the applied conditions. For a qualitative description of TNT-residues f ormed during the composting process, hulk soil and different soil fractions were subjected to solid-state N-15 NMR spectroscopy. Major resonance signa ls could be detected in the chemical shift regions of five-ring heterocycli c nitrogen and in the area of aniline derivatives and primary amines. Disti nct nitro peaks were found in the bulk samples and in the humic fractions o btained with a mild extraction procedure. This signal disappeared in the ma terial extracted with a more drastic procedure. Quantitative investigations of the N-15 distribution in the composted material revealed that 33% of th e stable nitrogen isotope was incorporated into the humic- and fulvic acid, and 23% was present in the humin. Furthermore 38.8% of the N-15 present in the composted material could be allotted to condensed TNT residues, wherea s 1.9% are assigned to nitro functions and 15.2% to amino functions. In the investigation presented here a bioremediation method was simulated with N- 15-TNT spiked soil. The nonradioactive label allowed a qualitative and quan titative characterization of residues of the explosive. Our results give st rong evidence for a stable incorporation of the nitroaromatics into the hum ic material of soils. However, further investigations will be necessary to prove a long-time stability of bound TNT residues and to assess toxicologic al effects of the treated soil.