Fate and metabolism of [¹⁵N]2,4,6‐trinitrotoluene in soil

Abstract

The fates of the labels from [14C] and [15N] trinitrotoluene were analyzed in bioreactors under aerobic conditions in soil treated by a fungal bioremediation process with Stropharia rugosoannulata and in control soil. Up to 17.5% of the 15N label had a different fate than the 14C label. Three N-mineralization processes were identified in detailed experiments with [15N]TNT. About 2% of the 15N label was found as NO3- and NH4+, showing simultaneous processes of direct TNT denitration (I) and reduction with cleavage of the amino groups (II). The enrichment of NO2-/NO3- (up to 7.5 atom% 15N abundance) indicates the formation of Meisenheimer complexes with a denitration of [15N]TNT. A 1.4% of the label was found distributed between N2O and N2. However, the 15N enrichment of the N2O (up to 38 atom%) demonstrated that both N atoms were generated from the labeled TNT and clearly indicates a novel formation process (III). We propose, as an explanation, the generation of N2O by cleavage from condensed azoxy metabolites. In addition, 1.7% of the 15N label was detected as biogenic amino acids in the wheat straw containing the fungus. Overall, 60 to 85% of the applied [15N]TNT was degraded and 52 to 64% was found as nonextractable residues in the soil matrix. Three percent was detected as 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene.

Transport and Immobilization of 2,4,6 15N-Trinitrotoluene in Soil Microcosms Subjected to Long Term Incubation Under Aerobic Conditions

“…Alternatively, they may point to the production of volatile N-compounds derived from the oxidative denitration of 15 N-TNT or by the biological transamination of the reduced transformation products. Such reactions were previously suspected to be in part responsible for elevated (NO 2 + NO 3 )-N concentrations observed in contaminated soils from a former ordnance plant (Comfort et al, 1995) and partly responsible for the 15 N add losses observed by Weiß et al (2004). In our study those reactions may also explain the presence of inorganic 15 N add in the leachate as it was assumed from its the low C t / 15 N add ratio and the solid-state 13 C NMR spectroscopic analysis.…”

“…Comparable decreases of recovery were recently observed during the aerobic degradation of grass material in the presence of 15 N-TNT (Knicker, 2003). Losses of up to 12% 15 N add were also detected for soils spiked with 15 N-TNT after 108 days of fungal bioremediation (Weiß et al 2004). Considering the continuity of the 15 N add -losses with increasing incubation time in the present experiment, they are not readily explainable by handling and sample preparation alone.…”

“…The fact that high 15 N add -yields were already detected in WE after this short period supports a fast transformation of TNT into more polar compounds. In aerobic environments, 2,4,-diamino-6-nitrotoluene was reported to represent an important reduction product in addition to amino dinitrotoluenes (Comfort et al, 1995;Major, 1999;Weiß et al, 2004). The monoamino components are about one-third as soluble as TNT but the diamino metabolites are substantially more soluble than TNT (Major, 1999).…”

Bioremediation of Explosive TNT by Trichoderma viride

“…This is usually accompanied by the production of light, heat, sound, and pressure. Nitro-aromatic and nitramine compounds, such as 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydrol-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), are common military explosives that are found in soils at destruction ranges, explosive dumping grounds, industrial production sites, firing ranges, and ammunition factories [1][2][3]. The United States Environmental Protection Agency (USEPA) has listed Nitro-substituted explosives, including TNT and RDX, as priority pollutants, whereas RDX, classified as a potential carcinogen that is toxic to organisms, is comparatively mobile in the soil, has a low rate of degradation in soil, and presents distinct problems for bioremediation.…”

Toxicological characterization of 2,4,6-trinitrotoluene, its transformation products, and two nitramine explosives

“…Release of 2,4,6-TNT to the environment represents a potential hazard because of the toxicity of 2,4,6-TNT itself, its metabolites from transformation, by-products of the manufacturing process, or incomplete combustion [1]. Furthermore, 2,4,6-TNT is a man-made substance and because of its low biodegradability it is persistent in the environment [2,3].…”