chromatography (RP-HPLC) (Thermoseparation Prod-
Table 3. Sampling dates and volumes of solution
ucts) on a 25- 4.6-cm LC-18 (Supelco) column. Sam-
added and removed on each date from each column.
ples were mixed 50:50 with acetonitrile prior to analy-
Sample
Volume added Volume removed
sis. The analytes were eluted with 35:65 (v/v)
date Chamber
(mL)
(mL)
methanol:aqueous buffer (100 mmol KH2PO4) adjust-
ed to pH 3.5 with acetic acid. Flow rate was 1.5 mL
13
1
25.2
min1. A standard solution containing RDX, TNT,
2
27.4
HMX, TNB, and 2 amino-DNT at concentrations of 1
3
19.2
mg L1 in acetonitrile was prepared following SW-846
4
17.4
Method 8330 (USEPA 1994). A standard solution of
26
1
37.5
42.0
picric acid in water at a concentration of 5 mg L1 was
2
25.8
28.0
prepared according to Thorne and Jenkins (1995).
3
36.4
33.5
4
28.2
30.0
Mass balance calculations
39
1
38.1
35.0
To calculate a mass balance of explosives in the
2
26.0
25.0
chambers, all concentrations were converted to mass
3
37.6
36.0
units (g). For the aqueous solutions, the following
4
26.0
26.0
equation was used:
67
1
36.3
35.5
2
33.0
26.0
mass of explosive (g)=
3
36.6
35.0
concentration of explosive (mg L1)
4
30.8
26.5
volume of solution added (input) or
81
1
40.0
37.5
removed (output) (L)
2
21.2
20.0
1000.
(1)
3
34.1
34.0
4
26.2
27.0
There was some error associated with the volume of
100
1
41.0
solution removed because some solution remained in
2
27.0
the extraction tube. The volume of solution added was
3
37.0
determined using a buret. To calculate the mass of explo-
4
28.0
sives in the soil, the following equation was used:
Totals
1
177.1
191.0
mass of explosive (g) =
2
133.4
126.0
3
163.9
175.5
concentration of explosive (g g1)
4
128.6
137.5
mass of dry soil (g). (2)
The mass of dry soil was estimated based on the weight
cric acid. Two 2-g subsamples of air-dried soil were
and moisture content of soil added at the beginning of
each placed in a 20-mL glass vial. Ten mL of acetoni-
the experiment. Soil was packed into the chambers in
trile was added to one vial of soil to extract RDX and
approximately 1-cm layers and was collected from the
TNT, while 10 mL of Milli-Q water was added to the
chambers in 2.5-cm, 1.5-cm, or 1-cm layers (Fig. 1).
other vial of soil to extract picric acid. The vials were
The dry weights of soil, determined at the beginning of
placed in an ultrasonic bath overnight to ensure maxi-
the experiment for each 1-cm layer, were added together
mum recovery of explosives from soil. To flocculate
to get the dry weight of the final sample.
solids after sonicating, 10 mL of a CaCl2 solution was
added to the vials with acetonitrile, and 10 mL of ace-
tonitrile was added to the vials with water. All samples
RESULTS
were centrifuged at 1500 RPM for five minutes and
filtered through a 0.5-m filter into sample vials. Cen-
Temperature profiles
Part of the technical challenge of this experiment
trifugation was used to facilitate sample flocculation.*
was to maintain a stable frozen barrier in the base of
Analyses of explosives and their transformation
the experimental chambers (Fig. 1). Temperature
products in aqueous solutions and soil extracts were
measurements at the four levels in the chambers (T1
performed by reverse-phase, high-performance liquid
T4) averaged ≈ 7, 1, 1.5, and 3.5C, respectively
(Fig. 2). The temperatures in the chambers fluctuated
* Personal communication, Philip G. Thorne, Geological Sciences
with changes in room air temperature. During the course
Division, CRREL, Hanover, New Hampshire, 1999.
4
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