Because the extracts had very high concentrations of TNT, DNT, or RDX, they were diluted by
introduction of microliter volumes of the acetone or methanol extracts into a measured volume of 1:1
methanol/water. Dilutions ranged from 1:100 to 1:10,000.
Field-contaminated soils
Several high-concentration field-contaminated soils from a number of installations were utilized
for this study. Initial experiments used archived soil samples that had been air dried, ground, and
thoroughly homogenized. These samples were rewetted with water prior to extraction to simulate
field conditions. To do so, about 4 mL of water was added to each 20-g sample of soil, mixed, and
allowed to stand for 30 minutes before adding the extracting solvent. Archived samples from Wel-
don Springs Army Ammunition Plant (AAP), Nebraska Ordnance Works, Iowa AAP, Volunteer
AAP, and Hawthorne AAP were used in this portion of the study.
Kinetic extraction tests were also conducted with undried soils from Volunteer AAP. These field-
moist samples were processed by removing large stones and thoroughly mixing prior to removing a
20-g subsample for extraction.
Protocol for kinetic extraction studies
A 20-g portion of field-moist soil was placed in a 125-mL (4 oz) polypropylene bottle containing
five stainless steel balls. A 100-mL aliquot of either acetone or methanol was added and the bottle
was capped and vigorously shaken for three minutes on a mechanical shaker. After the shaking
period, the soil was allowed to settle for about five minutes; a 2-mL aliquot was then removed and
passed through a 0.5-m Millex SR filter unit into a labeled autosampler vial. The Nalgene bottle was
then recapped and shaken for additional time increments. After each shaking time increment, soils
were allowed to settle and samples of the supernatant were collected and processed as above. When
all the kinetic samples were collected, portions of the filtered extracts were diluted into 1:1 metha-
nol/water and analyzed by RP-HPLC as described above.
Colorimetric field-screening analysis
Colorimetric analysis of the acetone extracts was conducted using the EnSys reagent. A reference
standard of TNT in acetone (containing 3% water) was prepared with a concentration of 3 mg/L.
This standard was analyzed with each set of samples and was used to establish the response factor
(RF-TNT) for estimating TNT concentration for the sample extracts. The filtered sample extracts
were diluted with acetone (containing 3% water) using a microliter syringe. A 25-mL portion of the
diluted extract was placed in a spectrophotometer cuvette and the initial absorbance (ABS-initial)
obtained at 540 nm on a Hach DR/2000 battery-operated spectrophotometer. The cuvette was then
removed from the spectrophotometer and one drop of the EnSys developer solution (referred to as
the EnSys reagent) was added. The contents of the vial were mixed thoroughly and allowed to stand
for one minute. The absorbance at 540 nm was then obtained (ABS-final) as described above. Dilu-
tions were made to obtain final absorbances below 1.0 A.U. after addition of the EnSys reagent. The
TNT concentration in the sample was calculated as follows:
TNT (g/g) = {[ (ABS-final) 2 (ABS-initial)] / RF-TNT} 5.
A response factor of 0.177 A.U./mg/L was obtained from calibration. The factor of 5 is used to con-
vert concentration in mg/L to concentration on a g/g basis. Results were then corrected for the
specific dilution used.
Results on moist samples from Volunteer AAP were obtained as described above except that the
soil extraction step was modified. A short kinetic study conducted at Volunteer revealed that extrac-
tions needed to be extended to get stable concentrations. Samples were shaken for three minutes,
allowed to stand for 30 minutes, and shaken for an additional three minutes. After allowing the soil
to settle, an aliquot was filtered, diluted using microliter syringes as described above, and analyzed
using the EnSys method.
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