cation concentration range where biodegradation
was obtained approximately 12 months prior to
is uninhibited for this soil was established, tests of
this study at the Cold Regions Research and Engi-
chemical preservation with MeOH and NaHSO4
neering Laboratory (CRREL). The soil was col-
were performed within the region where rapid
lected from the top horizon in an area where TCE
losses occurred. The experiment with NaHSO4 was
contamination has been present for about 20 years.
divided into two parts, one using high levels of
A bulk sample was prepared by air-drying, siev-
the analyte and headspace gas chromatography
ing through a 30-mesh screen and thoroughly mix-
(HS/GC) analysis, and the other using low levels
ing. This process reduced the background TCE
of the analyte and purge-and-trap gas chromatog-
concentration in the soil to below detection (<3
raphy mass spectrometry (PT/GC/MS) analysis.
ng/g).
Soil subsample preparation
Soil subsamples were prepared by transferring
EXPERIMENTAL METHODS
1.50 0.01 g of the bulk CRREL soil into 1-mL glass
The experimental approach used in this study
ampoules using a stainless steel spatula and a small
combined a laboratory fortification method that is
plastic funnel. As many as 21 soil subsamples were
analogous to an environmental pollution pathway
then placed inside a glass desiccator with CaSO4
with a handling protocol that does not expose the
for periods ranging between 24 and 48 hours. Af-
subsample to the atmosphere. Volatilization was
ter desiccation the CaSO4 was removed, and a va-
minimized by keeping the subsamples in gas-tight
por fortification solution contained in a 60-mL
volatile organic compound analysis (VOA) vials
glass bottle was introduced. Stock solutions for
during storage and analysis. This study also used
spiking the soil matrices were prepared by com-
the same bulk soil and experimental protocols that
bining approximately 0.27 g of Tol, 0.30 g of TCE,
resulted in the rapid loss of the two aromatic hy-
0.25 g of TDCE and 0.18 g of Ben and taking the
drocarbons Ben and Tol, presumably due to bio-
mixture to volume in 25 mL of tetraethylene gly-
degradation (Hewitt 1994c). All soil subsamples
col dimethyl ether (tetraglyme). This stock was fur-
were spiked with Ben, Tol, TDCE and TCE using a
ther diluted with tetraglyme as show in Table 1 to
vapor fortification treatment (Hewitt 1994d,e).
create specific soil VOC treatment levels for the
These four analytes were chosen because they are
different experiments. All of the chemicals were
frequently identified at hazardous waste sites
reagent-grade quality.
(Plumb and Pitchford 1985, Zarrabi et al. 1991) and
This method of soil subsample treatment relies
biodegrade either under anaerobic or aerobic con-
on the partial pressures of the analytes in the spik-
ditions.
ing solution to create a gaseous phase concentra-
Except when MeOH was used as a chemical
tion to impregnate the soil grain surfaces. After
three or more days of equilibration the desiccator
preservative, all fortified soil subsamples remained
was opened, and 5-mm-diameter glass beads were
in closed VOA vials throughout storage and analy-
placed on top of each of the ampoules, providing
sis. Vessels containing MeOH, which retards vola-
temporary caps. Then, without hesitation, the am-
tilization and inhibits biodegradation, can be
poules were positioned in a clamp and the necks
briefly opened to withdraw an aliquot without
were heat-sealed using a propane plumber 's torch.
large losses of the VOCs present as solutes. In con-
trast, soils and soil-water slurries with
volatiles present in the headspace must
Table 1. Fortification solutions.
be kept sealed because even rapid trans-
Volume
Volume
No. of subsamples
fers or brief exposures to the atmosphere
Experiment
of stock (mL) of tetraglyme (mL)
fortified
can result in large losses (Jenkins and
Schumacher 1987, Urban et al. 1989,
Analyte concentration
Siegrist and Jenssen 1990, Lewis et al.
A
0.1
10
6
B
0.5
9.5
6
1991, Hewitt et al. 1992, Voice and Kolb
C
2.0
8.0
6
1993).
NaHSO4 - HS/GC
0.1
10
21
Soil
The soil used here and previously is a
NaHSO4 - PT/GC/MS
0.01
10
14
silty sand with a 0.053% total organic car-
Immersion in MeOH
0.5
9.5
12
bon content. A bulk sample of this soil
2
Previous Page
