Sediment-Mediated Reduction of 2,4,6-Trinitrotoluene and Fate of the Resulting Aromatic (Poly)amines

Abstract

2,4,6-Trinitrotoluene is a major surface and subsurface contaminant found at numerous munitions production and storage facilities. The reductive transformation of 2,4,6-trinitrotoluene (TNT) to aromatic (poly)amines and the consequent fate of these products were studied in anaerobic and aerobic sediment−water systems. Reduction of TNT was rapid under both anaerobic and aerobic conditions. Nitro-reduction was regioselective, leading to the preferential formation of 4-amino-2,6-dinitrotoluene (4-ADNT) and 2,4-diamino-6-nitrotoluene (2,4-DANT). Subsequent sorption of 2,4-DANT was rapid under aerobic conditions and resulted in nearly complete, irreversible retention by the sediment phase. Under anaerobic conditions, the rapidly formed 2,4-DANT displayed little affinity for the sediment phase. Instead, 2,4-DANT was further transformed to products that remained in the aqueous phase. Sorption studies in nontransforming sediments indicated increased irreversible sorption with replacement of nitro groups with amino groups. Covalent binding of the DANTs was partially inhibited under anoxic conditions, but sorption of TNT and the ADNTs was unaffected by changes in redox conditions.

Summary Review of the Aquatic Toxicology of Munitions Constituents

“…When associated with organic matter in the water column, soil or sediment, TNT typically biotransforms, sometimes extensively, to reduced animated compounds, first to produce aminodinitrotoluene (Am-DNT) and preferentially 4-Am-DNT, with further reduction producing diaminonitrotoluene (DANT) and preferentially 2,4-DANT (Monteil-Rivera et al 2009). Strong sorption to sediment organic matter not explained by hydrophobic partitioning has been reported for freshwater (Elovitz and Weber 1999) and marine sediment (Pennington et al 2011). …”

“…Possible chemical reactions in the aquatic environment include hydrolysis, photolysis, thermolysis, and oxidation. A review of the Rosenblatt et al (1991), b from Elovitz and Weber (1999), c from Greenwald (1926), d This value is uncertain; range of cited values from 2.1 to 43 mg L -1 , e hexahydro-1,3,5-trinitro-1,3,5-triazine or cyclo-1,3,5-trimethylene-2,4,6-trinitramine, also known as cyclonite, f Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine physicochemical properties for major explosives and a discussion of their environmental fate in the marine environment are provided in Noblis (2011). Singh et al (2012) summarized information on the biodegradation and biotransformation pathways of major explosives.…”

“…In contrast, fewer studies addressed the fate of explosives and related compounds in sediments, despite the potential ecological risk associated with their presence in this compartment of aquatic environments. Recent studies characterizing the processes that occur following the initial contact of explosives and related compounds with sediments revealed rapid rates of transformation for a variety of nitroaromatic compounds (Elovitz and Weber 1999;Lotufo et al 2010c;Pennington et al 2011). …”

A Study on the Degradation Properties of Aqueous Trinitrotoluene by Palladium Catalyst and Formic Acid

“…TNT는 환원 분해 과정을 통해 nitro기가 amino 기로 치환되면서 연속적으로 2-amino-4,6-dinitrotoluene (or 4-amino-2,6-dinitrotoluene)으로 분해된 후 diaminonitrotoluene을 거쳐 triaminotoluene으로 전환되는 것으로 알려져 있다 (Elovitz and Weber, 1999). 아민기를 보유한 방향족 화합물은 여전히 독성을 나타내지만 TNT와 비교할 때 쉽 게 생분해된다 (Hundal et al, 1997).…”

Toxicity and bioaccumulation of TNT in marine fish in sediment exposures

“…Reduction of the nitro-groups to amino-groups typically follows introduction of TNT to soils (Pennington and Brannon, 2002) and sediments . The major aminated metabolites of TNT are 2-aminodinitrotoluene (2-ADNT) or 4-aminodinitrotoluene (4-ADNT) and 2,4-diaminonitrotoluene (2,4-DANT) or 2,6-diaminonitrotoluene (2,6-DANT) (Elovitz and Weber, 1999;Pennington and Brannon, 2002). …”