Solid-state nitrogen-15 nuclear magnetic resonance analysis of biologically reduced 2,4,6-trinitrotoluene in a soil slurry remediation

Soil contaminated with 2,4,6-trinitrotoluene (TNT) and spiked with [C-14]- and [N-15(3)]-TNT was subjected to an anaerobic-aerobic soil slurry treatme nt and subsequently analyzed by radiocounting and solid-state N-15 nuclear magnetic resonance (NMR) spectroscopy. This treatment led to a complete dis appearance of extractable radioactivity originating from TNT and almost all of the radioactivity was recovered in the insoluble soil fraction. As reve aled by solid-state N-15 NMR, a major fraction of partially reduced metabol ites of TNT was immobilized into the soil during the early stage of the ana erobic treatment, although some of the compounds (i.e., aminodinitrotoluene s and azoxy compounds) were extractable by methanol. Considerable N-15 inte nsity was assigned to condensation products of TNT metabolites. A smaller s ignal indicated the formation of azoxy N. This signal and the signal for ni tro groups were not observed at the end of the anaerobic phase, revealing f urther reduction and/or transformation of their corresponding compounds. An increase of the relative proportion of the condensation products occurred with increasing anaerobic incubation. Aerobic incubation resulted in a furt her decrease of aromatic amines, presumably due to oxidative transformation s or their involvement in further condensation reactions. The results of th e study demonstrate that the anaerobic-aerobic soil slurry treatment repres ents an efficient strategy for immobilizing reduced TNT in soils.