Table 1. Concentration of aqueous stock solutions and preparation vol-
umes for the aqueous analyte spiking solution.
Conc. in aqu.
tered through 0.45-mm nylon membranes into clean,
analyte aqueous spiking solution was added. The tar-
amber glass jugs. No solvents, other than water, were
get concentration of the analytes in the soil was
used in the preparation of these solutions. The concen-
approximately 0.5 mg/kg for the nitroaromatics and 0.14
tration of each solution was determined by RP-HPLC.
mg/kg for RDX.
A combined-analyte spiking solution of the key com-
After spiking, samples 1 to 33 were placed in a low-
temperature incubator at 4 2C, samples 34 to 63
ponents was prepared by combining appropriate vol-
were placed in a refrigerator at 4 2C, and samples
umes of each of the individual aqueous solutions (Table
1) and diluting to 1 L in a volumetric flask. This solu-
64 to 84 were placed in a cabinet at room temperature
(22 2C) in the dark. Samples 85, 86, and 87 were the
tion included 1,3-DNB, 2,4,6-TNT, 2,4-DNT, and 2,6-
DNT. RDX was also included, because previous
blanks (deionized water spiked) and samples 88, 89,
research indicated that it was quite stable in soil and
and 90 were the time 0 samples. The time 0 samples
could serve as an internal standard to account for any
were spiked with the aqueous solution of explosives,
minor differences in spiking volume from replicate to
followed immediately by 10 mL of AcN. This was done
replicate. This solution was filtered through a 0.45-mm
to minimize the opportunity for analyte loss and allow
nylon filter, then transferred to a brown glass jug and
for the accurate determination of the initial concentra-
stored in a refrigerator at 4C. The aqueous solution
tion of analytes in the samples.
was analyzed by HPLC. The determined concentrations
Four hours from the time of spiking, triplicate sample
are presented in Table 1.
vials from each storage temperature were selected at
random. The samples from the lower temperatures were
briefly allowed to warm to room temperature. A 10-mL
The soil used for this study was obtained from the
aliquot of AcN was added to each of the nine samples.
research minefield at Fort Leonard Wood. The soil was
These samples, along with the three time 0 samples,
air-dried, ground with a mortar and pestle, and sieved
were extracted overnight using ultrasonication. The
through a no. 40 (425-mm) sieve. Replicate 5.0 0.1-g
extracts were then analyzed by HPLC.
subsamples were weighed into individual 20-mL glass
The remaining samples were treated in an identical
manner after additional storage at one of the three tem-
peratures. Subsequently, triplicate samples from each
Soil wetting and analyte spiking
storage temperature were extracted and analyzed on
Prior to the start of the experiment, we rewetted the
days 1, 3, 7, 13, and 20. Because of the rapid rate of
previously air-dried test soil by adding 1.00-mL aliquots
analyte transformation at room temperature, samples
of water to each replicate. The samples were then
from this storage temperature were also run on day 9.
For samples stored at 4 and 4C, triplicates were also
allowed to stand at room temperature in the dark for 3
days to allow microbiological activity to be reestab-
run on day 30.
lished (Maskarinec et al. 1991).
In addition to determining the concentrations of the
The soil samples were fortified by carefully adding
key components, we also determined the concentrations
1.00 mL of solution to each individual vial; 90 indi-
of the monoamino reduction products of each
vidual vials were spiked. To three of the replicates, 1.0
nitroaromatic. These included 3-nitroaniline (3-NA),
mL of reagent grade water was added as a blank, and,
6-amino-2-nitrotoluene (6-Am-NT), 2-amino-4-
to the remaining 87 replicates, 1.0 mL of the combined
nitrotoluene (2-Am-NT), 4-amino-2-nitrotoluene (4-