above the soil surface in which equilibrium between
detect metal mines will be much more difficult to do
the surface soil and that air layer is established, for an
than using them to detect plastic ones.
equal concentration of 2,4-DNT and 2,4,6-TNT in the
The overall soil sampling program at the Fort
soil, there would be a 43 times higher concentration of
Leonard Wood minefield detected 20 individual ERCs
2,4-DNT in the air than 2,4,6-TNT. Similarly, for the
in one or more soil samples collected near the buried
two ADNTs, there would be 15 times higher 2,4-DNT
mines. This includes a number of isomers of trinitro-
than 4-ADNT, and 18 times higher 2,4-DNT than 2-
toluene, dinitrotoluene, and dinitrobenzene, various
ADNT. Since the surface soil at the Fort Leonard Wood
amino transformation products of the trinitro- and
site generally contains higher levels of 2,4-DNT and
dinitrotoluenes and benzenes, 1,3,5-TNB, and RDX.
the ADNTs than 2,4,6-TNT, the vapor evolving into
Of these, the chemicals that were most often detected
the boundary layer above the mines and providing the
in surface soils above buried mines were 2-ADNT, 4-
chemical vapor signature for the mines should largely
ADNT, and 2,4-DNT. Even though 2,4,6-TNT accounts
be 2,4-DNT, 4-ADNT, and 2-ADNT, with only a
for greater than 98% of the high explosive in a number
minor contribution from 2,4,6-TNT and other ERCs.
of the land mines at the Fort Leonard Wood minefield,
it was detected in surface soils less often and at lower
concentration than 2,4-DNT and the two ADNTs. Both
CONCLUSIONS AND IMPLICATIONS FOR
2,4,6-TNT and 1,3-DNB are important components of
CHEMICAL DETECTION OF LAND MINES
the flux from many of these mines (George et al. 1999),
but these two chemicals do not accumulate in the soil
It can be argued that the source of any ERCs that
to the same degree as does 2,4-DNT. The difference
are evolving into the air above buried land mines is
appears to be attributable to the much greater environ-
surface soil that is contaminated with trace levels of
mental stability of 2,4-DNT compared to 2,4,6-TNT
these ERCs. If that is true, the results of these soil analy-
and 1,3-DNB (Miyares and Jenkins, in press). The trans-
ses have enormous implications for our ability to de-
formation of 2,4,6-TNT accounts for the presence of
tect buried land mines using ERCs.
the two ADNTs and they seem to have a much greater
Clearly, the results of over 1000 soil analyses show
environmental persistence than 2,4,6-TNT. Likewise,
that the concentrations of ERCs present in soils near
1,3-DNB is transforming to 3-NA; however, 3-NA does
buried mines vary tremendously, depending on the spe-
not appear to be accumulating to the same degree as
cific type of mine. Of the mines we studied, the plastic-
the ADNTs, although 3-NA was only targeted in two of
cased TMA-5 antitank mine produced the largest con-
the five sampling episodes. This is probably caused by
centrations of ERCs in the soils, followed by the PMA-
a faster rate of further reaction for 3-NA, in which the
1A antipersonnel mine. We observed very little accu-
amine function is much more basic than in the ADNTs,
mulation of ERCs around the metal-cased TMM-1 an-
owing to the presence of only one nitro group on the
titank mine or the small PMA-2 antipersonnel mine,
aromatic ring, compared with two for the ADNTs. In-
and it appears that these mines would be very difficult
creased basisity probably causes a more rapid reaction
to find using chemical sensors based on vapor detec-
with soil organic matter that is analogous to that shown
tion. We have only preliminary information on the types
to occur for the ADNTs (Thorne and Leggett 1997,
and concentrations of ERCs originating from Type 72
Pennington et al. 1999).
antitank mines, but it appears that the same suite of
The distribution of ERCs in the surface soils near
compounds, with the addition of RDX, will evolve into
buried mines is spatially heterogeneous. For example,
the soil, as found for the TMA-5 and PMA-1A mines,
excluding the initial sampling, ERCs were detected in
but the resulting soil concentrations may be lower.
37% of the surface soils samples collected near TMA-
Surface contamination on TMM-1 mines that had
5 mines and in 36% of the surface soils collected near
been in the ground for over a year was largely gone.
PMA-1A mines. ERCs were most often found in a dis-
Apparently, leakage of ERCs from this metal-cased
continuous halo around the perimeter of the mines, with
mine was minimal and does not contaminate the sur-
little or no signature being detected directly over their
face of the mine, at least not the areas that were swiped.
centers. Analytes were detected in some surface soils
This finding is consistent with our failure to detect sig-
collected 20 cm away from the perimeters of the mines,
nificant ERCs in the soil near the TMM-1 mines after
which was as far away from the mines as samples have
they had been in the ground for several months. Com-
been collected thus far.
paring the TMM-1 with a similar sized plastic-cased
While ERCs are also very heterogeneously distrib-
mine (TMA-5) tells us that the metal casing is a much
uted in the subsoil, their concentrations decline with
more effective barrier to the release of signatures than
distance from the mine. For example, soil concentra-
tions of 873, 5480, 3430, 2802, and 524 g/kg were
is the plastic casing. Hence, using vapor signatures to
34
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