faces continue to extract contamination.* We think this
Table 1. Summary of surface concentrations on
is to be expected, because paint and plastic are three-
landmines sampled at the Naval Ordnance Sta-
dimensional reservoirs that can renew their surface con-
tion in 1992 (ng/cm2).
tamination by outward permeation; enhanced recovery
may also result from inward solvent penetration. Thus,
TNT
2,4-DNT
RDX
there is always a kinetic aspect owing to transport of
signature through the material and to the surface from
Min.
<2
<2
<2
within. This is especially true of plastics, which are com-
Max.
540
570
590
Mean
74
32
30
monly used in casings, but also of painted metal. The
Median
12
<2
7
rate of explosive permeation through plastics is under
investigation and will be reported elsewhere (Leggett
and Cragin, in prep.).
This study included surface samples from four types
tity of RDX/HMX also suggests that the explosive was
of Yugoslavian landmines. All of the landmines sampled
not cast TNT, but a mixture of TNT and RDX such as
had been in storage for 4050 years and had never been
Composition B. Published information on explosive fills
emplaced. Most of these mines were sampled at Fort
is not always reliable.
Leonard Wood, Missouri, in July of 1998, where the
Most of the mines contained RDX and TNT, and RDX
ambient conditions were sunny, hot, and windy. A
was found nearly as frequently as TNT in the swabs.
smaller number were transported to CRREL and
Vapor phase transport of RDX seems unlikely because
sampled under controlled environmental conditions.
of its low volatility, some 3 orders of magnitude lower
Paper filter disks, 1.5 cm in diameter, were saturated in
than that of TNT, and suggests that contamination
methanol and placed randomly over the mine surfaces.
arrived on the surface by direct contact. Small amounts
Upon drying they were picked up with forceps and
of TNT degradation products, TNB and amino-
transferred to an amber vial containing acetonitrile.
dinitrotoluenes, were often found as well. Measured
Multiple disks were composited to form a single sample.
surface concentrations of the major contaminants on
The number of disks per mine was keyed roughly to
all but the TMA3 (Appendix A) are summarized in Table
the size of its surface. Except for the PMA2, no more
1. The detection limit for these analytes was about 2
than 2% of the surface was taken up by the disks. Esti-
mated mine surface areas and numbers of disks per
all contaminants and are highly skewed, with the
sample are given in Table 2. The vials were kept at
median value much lower than the mean.
4C for storage and transport to the lab, where analy-
sis was done. Analyses were completed within a week
of sampling by gas chromatography with electron cap-
METHODS
ture detection (Walsh and Ranney 1998).
In choosing to alter the procedure from that used in
Some caveats about swabbing as a method of sur-
1992, we attempted to circumvent some of the known
face sampling should be given. The original work of
Hogan et al. (1992) used commercial cotton swabs (Q-
tips) and acetone solvent, which is invasive to paints
and plastics. Subsequently, it was shown that serial ac-
*Personal communication with P.J. Rodacy, Sandia National
etone swabs over the same area of painted metal sur-
Laboratories, 1996.
Table 2. Mine characteristics and sampling parameters.
Area
Number of
Percentage
(cm2)
Mine
Material
disks
of area
PMA1A-AP
PVC*
345
4
2
PMA2-AP
PS**
118
3
4
TMA5-AT
PS
2720
15
1
TMM1-AT
painted steel
2240
10
1
*Polyvinylchloride.
**Polystyrene.
2
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