holding time of 6 weeks at 4C for 1,3,5,7-octahydro-
the stability of TNT in soil varies with soil type and
1,3,5,7-tetranitrotetrazocine (HMX), 1,3,5-hexahydro-
location. Results in the present study showed that TNT
1,3,5-trinitrotriazine (RDX), and 2,4-dinitrotoluene
degraded much faster in a Charlton sandy loam col-
(2,4-DNT), and several weeks at 20C for 2,4,6-trini-
lected in New Hampshire than in a deep aquifer sand
trotoluene (TNT). Although the study was carefully con-
collected in Louisiana.
ducted and extensive data were collected, the work may
Dubois and Baytos (1991) also investigated the sta-
have been flawed by the use of the AcN. The effect of
bility of TNT in soil. In their study, however, they bur-
the AcN on the soil biota is unknown but, more impor-
ied a solid chunk of TNT and studied the reduction in
tantly, soil being stored for analysis does not contain
mass over 20 years. They concluded that the TNT
any AcN. Thus, the samples used do not mimic real
exhibited a half-life of about a year. It is unlikely,
sample. In fact, AcN is the solvent of choice for the
though, that the mechanisms controlling the rate of TNT
extraction of nitroaromatics and nitramines from soil
loss in that study are similar to those that control the
(Jenkins and Grant 1987).
rate of transformation of TNT when it is present at the
In 1993, a similar study was conducted in our labo-
parts-per-billion level in soil.
ratory to determine the pre-extraction holding times for
Objective
select nitroaromatics and nitramines in soil (Grant et
al. 1993, 1995). In this study, replicate 5-g samples of
The objective of this study is to estimate the stabil-
three different soils, Fort Edwards clay, Charlton sandy
ity (half-lives) of the major land mine signature com-
loam, and Windsor silt, were prepared first by rewetting,
ponents in soil from a research minefield at Fort Leonard
and then spiking with an aqueous solution of TNT, 2,4-
Wood, Missouri, at various environmental temperatures.
DNT, RDX, HMX, and 1,3,5-trinitrobenzene (TNB).
These results will be used to help us understand the
Three storage conditions were examined, room tem-
rate of accumulation of explosives signatures in soils
perature (22 2C), refrigerator storage (2 2C), and
adjacent to buried land mines at the research minefield.
freezer storage (15 2C). Triplicate samples from
In addition, the stability exhibited in this soil will be
each storage temperature were extracted after 0, 3, 7,
compared with that found for several other soils.
14, 28, and 56 days and the concentration of the analytes
determined. The results indicated that both TNB and
EXPERIMENTAL METHODS AND MATERIALS
TNT degraded very rapidly at room temperature, so
rapidly that some losses were observed even in the day
Chemicals
0 samples, which were extracted only 2 hours after spik-
ing. Grant et al. (1993) go on to report significant losses
All standards and test solutions were prepared from
of TNT and TNB at refrigerator temperatures at 7 days
Standards Analytical Reference Materials (SARM)
for all three soils and, at freezer temperatures, no losses
obtained from the U.S. Army Environmental Center
in the Charlton and Windsor soil, but slight losses in
(AEC), Aberdeen Proving Ground, Maryland. Aque-
the Fort Edwards soil at 56 days. The loss of TNT and
ous standards and test solutions were prepared in
TNB was coincident with the formation of the corre-
reagent grade water obtained from a Milli-Q Type 1
sponding monoamino transformation products pre-
Reagent Grade Water System (Millipore Corp.). The
dicted, based on the work of McCormick et al. (1976).
isopropanol (IPA) used to prepare the HPLC eluent and
In contrast, Grant et al. (1993, 1995) found that 2,4-
the acetonitrile (AcN) used for soil extractions were
DNT was much more stable than TNT or TNB. At room
HPLC grade from Burdick and Jackson. RP-HPLC elu-
temperature, 68% of the 2,4-DNT was still present
ent was prepared by combining water and IPA at a ratio
after 3 days, compared to less than 10% for both TNT
of 85/15 (v/v) and vacuum filtering through a nylon
and TNB. As the temperature decreased, the 2,4-DNT
membrane (0.2 mm) to degas and remove particulate
showed even greater stability. HMX and RDX were
matter.
found to be even more stable than 2,4-DNT. For these
Spiking solutions
two nitramines, no significant losses of analytes were
detected at any temperature or in any of the soils for
Aqueous solutions of the key components of TNT
the full 56 days. Overall, these results demonstrated
vapor (Jenkins et al., in press), TNT, 1,3-dinitroben-
significant variability in the stability of the major com-
zene (DNB), 2,4-DNT, 2,6-dinitrotoluene (2,6-DNT),
ponents of explosives between various soils and at dif-
and the internal standard, RDX, were prepared from
ferent temperatures.
SARMs. A small mass of each compound was placed
In a study investigating the use of stable isotope
in a 4-L amber glass bottle to which reagent grade
measurements as a means of monitoring the natural
water was added. The contents were stirred at room
attenuation of TNT, Miyares et al. (1999) found that
temperature for a week. The solutions were then fil-
2
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