Estimating the Half-Lives of Key Components
of the Chemical Vapor Signature of
PAUL H. MIYARES AND THOMAS F. JENKINS
INTRODUCTION
signatures through the soil to the surface and provided
Detection and elimination of buried land mines
some initial estimates for the surface-soil-to-air parti-
remains an important and intractable problem in many
tion coefficients for signature chemicals at the
countries throughout the world. The use of plastic cases
soil/atmosphere interface (Jenkins et al., in press).
on mines has reduced their detectability using magne-
In the study presented here, we will investigate the
tometry, and geophysical techniques, such as ground
degradation rates of key components of the chemical
penetrating radar, suffer high levels of false positives.
vapor signatures of explosive charges in land mines
An approach that is currently under investigation is
resulting from the mines being buried. We will esti-
chemical detection of vapors that evolve from explo-
mate the half-lives for these chemical components in
sives and are transported to the air or surface soil in the
soil from a research minefield at Fort Leonard Wood,
immediate vicinity of buried land mines. The success
Missouri, at several different temperatures, and com-
of canines in locating buried mines has demonstrated
pare the stability observed with that found for these
that there are detectable scents (chemical signatures) at
compounds in several different soils.
the surface in the vicinity of these mines. Research is
currently underway in our laboratory and elsewhere to
Background
determine the qualitative and quantitative nature of the
The pathway for reductive transformation of
chemical signatures originating from the explosives
nitroaromatics was first presented by McCormick and
within the land mines that may be detectable at the sur-
co-workers (McCormick et al. 1976). For 2,4,6-TNT,
face above buried mines. One of the critical elements
one of the three nitro groups on the aromatic ring is
in this investigation is the stability of the key compo-
reduced stepwise through nitroso and hydroxylamine
nents of the vapor once it enters the soil.
groups, resulting in the formation of two isomeric trans-
The ultimate goal of our research is predicting the
formation products, 2-amino-4,6-dinitrotoluene
composition and concentrations of land mine signatures
(2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT).
at the surface above buried mines. A further goal is to
These two compounds are relatively stable under aero-
predict these under various environmental conditions.
bic conditions, and have been routinely observed in
For example, the chemical composition of the explo-
TNT-contaminated surface soils (Walsh et al. 1993).
sive charge in several types of foreign land mines was
The question of the stability of nitroaromatic and
determined (Leggett et al. 1977) and laboratory experi-
nitramines in soil was first addressed by Maskarinec
ments have estimated the equilibrium headspace con-
et al. (1991) during a study conducted to deter-
centrations of explosives signatures associated with a
mine the pre-extraction holding times for soil samples
number of military-grade TNTs (Jenkins et al., in press).
collected at explosives-contaminated sites. In his stud-
Experiments with a number of intact mines and mine
ies, Maskarinec rewetted the soil to reestablish micro-
surrogates have been conducted to estimate the flux of
biological activity, then spiked each sample with the
these compounds through the mine casing at tempera-
explosives of interest dissolved in acetonitrile (AcN).
tures ranging from 4 to 32C (Leggett et al., in prep.).
A total of 2 mL of AcN was added to each 2-g
An initial study investigated the rate of transport of these
sample. From his results, Maskarinec recommended a
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