Investigations of Explosives and Their Conjugated Transformation
Products in Biotreatment Matrices
PHILIP G. THORNE AND DANIEL C. LEGGETT
aminodinitrotoluene isomers (ADNTs), 4-amino-
INTRODUCTION
2,6-dinitrotoluene (4ADNT) and 2-amino-4,6-
Previous work on biotreatment of TNT-
dinitrotoluene (2ADNT), and two diamino-
contaminated soils indicates that TNT is rapidly
nitrotoluene isomers (DANTs), 2,4-diamino-
converted to solvent-extractable transformation
6-nitrotoluene (2,4DANT) and 2,6-diamino-4-
products and to residues that are conjugated in a
nitrotoluene (2,6DANT). The condensation of hy-
non-solvent-extractable form (Kaplan and Kaplan
droxylamine intermediates to form azoxy dimers
1982, Caton et al. 1994, Pennington et al. 1995).
has also been reported (McCormick et al. 1976,
Plants grown hydroponically in TNT solutions
Kaplan and Kaplan 1982, Spanggord et al. 1995).
metabolized TNT reductively and transformation
The reduction pathways for TNT appear to be es-
residues were partially conjugated in a non-
sentially the same in a wide diversity of species
solvent-extractable form (Palazzo and Leggett
and environmental systems, including mammals,
1986a, b; Harvey et al. 1990). A considerable quan-
higher and lower plants, bacteria, soil, activated
tity of the two aminodinitrotoluene (ADNT) trans-
sludge, and compost. However, the predominant
formation products was released by acid hydroly-
amino isomer is 4ADNT in aerobic systems and
sis of the harvested plants after first extracting
2ADNT in anaerobic systems (Carpenter et al.
unconjugated transformation products with ben-
1978, Pennington 1988, Harvey et al. 1990).
zene (Palazzo and Leggett 1986a, b).
The experiments of Thorn et al. (1996 a, b)
using 15N-NMR to study covalent conjugation of
In experiments at Oak Ridge National Labora-
tory, base hydrolysis following solvent extraction
the aromatic amine aniline to humic substances
recovered an additional 60% of the applied radio-
and whole peat provide the best model for explain-
label from TNT/soil composts after 90 days (Caton
ing the fate of aromatic amine and diamine TNT
et al. 1994). Although the hydrolysates were not
transformation products. Aniline was reacted with
analyzed for specific TNT transformation prod-
purified humic and fulvic acids, silt loam soil, and
ucts, the analogy between living plants and
peat. Analyses of the solid- and liquid-state spec-
remediation systems containing mostly plant mat-
tra proved that aniline was readily incorporated
ter and wastes suggested that standard high-
into soluble and insoluble humic materials
pressure liquid chromatography (HPLC) analysis
through the formation of anilinohydroquinone,
of hydrolysates could be used to identify and
anilinoquinone, anilide, heterocyclic, and imine
quantify conjugated TNT residues in compost and
bonds by nucleophilic addition reactions. Prelimi-
digester sludge.
nary experiments with aniline/humic conjugates
TNT transformation and disposition in the en-
indicate that the imine and anilide bonds are hy-
drolyzable, while the anilinoquinone, anilino-
vironment has been thoroughly discussed in sev-
hydroquinone, and heterocyclic N-bonds are not.
eral reviews (McCormick et al. 1976, Walsh 1990,
Recently, Thorn (1997) showed that the same types
Gorontzy et al. 1994). The biological reduction of
of bonds are formed when the ADNTs and DANTs
the nitro groups on TNT proceeds through nitroso
are reacted with soil humic acids. Because both
and hydroxylamine intermediates to two
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