ENVIRONMENTAL FATE OF EXPLOSIVES

TR02-1(ERDC-CRL)
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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

al. 1997).

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