Guide for Characterization of Sites Contaminated with Energetic Materials
ENVIRONMENTAL FATE OF EXPLOSIVES
The behavior of explosives exposed to environmental conditions should be
considered when characterizing a contaminated site. The environmental fate of
TNT, RDX, and HMX can be attributed to three chemical properties:
1. Molecular structure
2. Water solubility
3. Adsorption to soil particles.
For instance, TNT is a nitroaromatic and tends to degrade by photolysis,
while nitramines like RDX and HMX do not. TNT is also more soluble and
dissolves more rapidly in water than RDX or HMX (HMX being the least solu-
ble). TNT can degrade into 21 metabolites with various solubilities and toxicities.
For example, the aminodinitrotoluenes that result from the photolysis or bio-
degradation of TNT are much more soluble than the parent compound, but they
can covalently bind to humic acid. Therefore, these metabolites are stabilized by
the formation of an amide with the organic contents of the soil. Moreover, in
soils that contain clays, sorption mechanisms are stronger with TNT and its
metabolites than for RDX and HMX, which adsorb very poorly to clay minerals
(Pennington and Patrick 1990, Haderlein 1996, Townsend and Myers 1996, Li et
Therefore the relative rates of soil leaching of these three explosives can be
explained in terms of the relative water solubilities and adsorption strengths.
RDX leaches out faster than TNT, which in turn leaches out faster than HMX.
TNT and its metabolites are more soluble than RDX, but their migration is
inhibited by strong bonding interactions with soil constituents. On the other
hand, HMX has a tendency to remain at the surface of the soils, because it is
almost insoluble in water.
Interactions with the soil are an important factor when characterizing explo-
sives in terms of bioavailability and extractability. TNT is particularly difficult to
characterize because it is easily reduced to amino degradation products, namely
2- and 4-amino-dinitrotoluene (ADNT), 2,4- and 2,6-diamino-nitrotoluene
(DANT), and, under anaerobic conditions, 2,4,6-triaminotoluene (2,4,6-TAT).
The characterization of TNT derivatives is important in establishing the overall
toxicity, remediation, transport, and extractability of TNT. The adsorption and
desorption characteristics of TNT and its metabolites are important physical