SPECIAL REPORT 95-5

Chemical Preservation of

Volatile Organic Compounds in

Soil Subsamples

Alan D. Hewitt February 1995
Abstract

This study evaluated chemical preservation as a means of inhibiting the biological degradation of volatile organic compounds (VOCs) in soil subsamples

held for 14 days or longer. Experiments were performed using a soil in which

benzene and toluene were found to rapidly biodegrade under aerobic conditions while following protocols consistent with high-level (VOCs at >1 μg/g)

and low-level (VOCs at <1 μg/g) purge-and-trap gas chromatography mass

spectrometry and static headspace gas chromatography analysis. Chemical

preservation consisted of immersing soil subsamples fortified with trans-1,2-

dichloroethylene (TDCE), trichloroethylene (TCE), benzene and toluene in

methanol or water acidified to a pH of less than 2 with NaHSO4. These two

methods of chemical preservation resulted in stable concentrations of these

two aromatic hydrocarbons even when held at room temperature. The two

chlorinated hydrocarbons showed stable concentrations with and without

chemical preservation. This result, in conjunction with earlier findings, suggests that chemical preservation is more effective at suppressing biodegradation than the current practice of refrigeration (4°C).

For conversion of SI metric units to U.S./British customary units of measurement

consult ASTM Standard E380-89a, Standard Practice for Use of the International

System of Units, published by the American Society for Testing and Materials,

1916 Race St., Philadelphia, Pa. 19103.

This report is printed on paper that contains a minimum of 50% recycled

material.
Special Report 95-5

Chemical Preservation of

Volatile Organic Compounds in

Soil Subsamples

Alan D. Hewitt February 1995

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

SFIM-AEC-ET-CR-95007

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Alan D. Hewitt, Research Physical Scientist, Geological

Sciences Branch, Research Division, U.S. Army Cold Regions Research and Engineering

Laboratory, Hanover, New Hampshire.

Funding for this work was provided by the U.S. Army Environmental Center, Martin H.

Stutz, Project Monitor. The author thanks Marianne Walsh and Dr. Thomas Jenkins for

critical reviews of the text and Chad Pidgeon for assistance in analyzing some of the samples.

This publication reflects the view of the author and does not suggest or reflect policy,

practices, programs or doctrine of the U.S. Army or the government of the United States. The

contents of this report are not to be used for advertising or promotional purposes. Citation

of brand names does not constitute an official endorsement or approval of the use of such

commercial products.

ii
INTRODUCTION

Soil samples collected during hazardous waste

site investigations for determining the presence

and concentration of volatile organic compounds

(VOCs) can be stored, according to current protocols, for up to 14 days at 4°C prior to analysis (U.S.

Environmental Protection Agency 1986). Laboratory studies addressing this holding period

have shown large losses of VOCs when soil subsamples were held under these conditions (Jackson et al. 1991, Maskarinec et al. 1992, King 1993).

In addition, studies associated with site investigations using bulk sample collection and handling

protocols have shown that the length of storage is

an important variable affecting the VOC concentrations (Hewitt 1994a,b). In general, the losses observed during these studies were correlated with

analyte vapor pressure and were independent of

analyte chemistry, i.e. halogenated recalcitrant

compounds were lost as fast as readily degradable

hydrocarbons (Suflita 1989, Russell et al. 1992). For

these reasons the observed reductions in VOC concentrations can be attributed to volatilization.

To my knowledge there has only been one study

that has clearly demonstrated that VOC concentrations in soil are subject to loss mechanisms independent of volatilization when refrigerated at

4°C and stored for 14 days (Hewitt 1994c). This

study demonstrated that under aerobic conditions,

concentrations of trans-1,2-dichloroethylene

(TDCE) and trichloroethylene (TCE) tend to remain

stable, while benzene (Ben) and toluene (Tol) levels rapidly decrease, sometimes to below detection. The rate of loss of these two hydrocarbons

was even greater when subsamples were held at

room temperature (22°C). The observed losses

were consistent with the published degradation

half-lives extrapolated from aqueous aerobic systems: 4 to 22 days for Ben and Tol and 4 weeks to 1

year for TDCE and TCE (Printup 1991). Thus, even

though the breakdown products were not identified, the results for aqueous media strongly suggest that the losses of Ben and Tol were due to biodegradation (Hewitt 1994c).

For this reason, when soils subsamples are held

up to 14 days prior to analysis, preservation measures other than, or in addition to, refrigeration

are necessary to inhibit the biological degradation

of some VOCs. Two logical methods of chemical

preservation are the use of acids and solvents.

Acidification to a pH of 2 is already a recommended practice for water samples collected for the analysis of VOCs, while solvents are often used to

extract these compounds from soils, particularly

when concentrations are expected to exceed 1 μg/g

(U.S. Environmental Protection Agency 1986).

For this study methanol (MeOH) and sodium

bisulfate (NaHSO4) were the solvent and acid

tested. Methanol is often the solvent of choice for

the extraction and dilution of VOCs, while the sodium salt of sulfuric acid has been successfully

used to inhibit biodegradation of VOCs in laboratory water, surface water and groundwater samples (Maskarinec et al. 1990). In addition to using

MeOH and NaHSO4 as chemical preservatives, an

experiment was performed to determine if elevated concentrations of the VOCs could suppress

biological activity.

This study, then, consisted of four experiments.

The first experiment varied the analyte concentration while following the protocols that successfully

demonstrated the biological degradation of aromatic compounds (Hewitt 1994c). After the fortifiChemical Preservation of

Volatile Organic Compounds in

Soil Subsamples

ALAN D. HEWITT
cation concentration range where biodegradation

is uninhibited for this soil was established, tests of

chemical preservation with MeOH and NaHSO4

were performed within the region where rapid

losses occurred. The experiment with NaHSO4 was

divided into two parts, one using high levels of

the analyte and headspace gas chromatography

(HS/GC) analysis, and the other using low levels

of the analyte and purge-and-trap gas chromatography mass spectrometry (PT/GC/MS) analysis.

EXPERIMENTAL METHODS

The experimental approach used in this study

combined a laboratory fortification method that is

analogous to an environmental pollution pathway

with a handling protocol that does not expose the

subsample to the atmosphere. Volatilization was

minimized by keeping the subsamples in gas-tight

volatile organic compound analysis (VOA) vials

during storage and analysis. This study also used

the same bulk soil and experimental protocols that

resulted in the rapid loss of the two aromatic hydrocarbons Ben and Tol, presumably due to biodegradation (Hewitt 1994c). All soil subsamples

were spiked with Ben, Tol, TDCE and TCE using a

vapor fortification treatment (Hewitt 1994d,e).

These four analytes were chosen because they are

frequently identified at hazardous waste sites

(Plumb and Pitchford 1985, Zarrabi et al. 1991) and

biodegrade either under anaerobic or aerobic conditions.

Except when MeOH was used as a chemical

preservative, all fortified soil subsamples remained

in closed VOA vials throughout storage and analysis. Vessels containing MeOH, which retards volatilization and inhibits biodegradation, can be

briefly opened to withdraw an aliquot without

large losses of the VOCs present as solutes. In contrast, soils and soil-water slurries with

volatiles present in the headspace must

be kept sealed because even rapid transfers or brief exposures to the atmosphere

can result in large losses (Jenkins and

Schumacher 1987, Urban et al. 1989,

Siegrist and Jenssen 1990, Lewis et al.

1991, Hewitt et al. 1992, Voice and Kolb

1993).

Soil

The soil used here and previously is a

silty sand with a 0.053% total organic carbon content. A bulk sample of this soil

was obtained approximately 12 months prior to

this study at the Cold Regions Research and Engineering Laboratory (CRREL). The soil was collected from the top horizon in an area where TCE

contamination has been present for about 20 years.

A bulk sample was prepared by air-drying, sieving through a 30-mesh screen and thoroughly mixing. This process reduced the background TCE

concentration in the soil to below detection (<3

ng/g).

Soil subsample preparation

Soil subsamples were prepared by transferring

1.50 ± 0.01 g of the bulk CRREL soil into 1-mL glass

ampoules using a stainless steel spatula and a small

plastic funnel. As many as 21 soil subsamples were

then placed inside a glass desiccator with CaSO4

for periods ranging between 24 and 48 hours. After desiccation the CaSO4 was removed, and a vapor fortification solution contained in a 60-mL

glass bottle was introduced. Stock solutions for

spiking the soil matrices were prepared by combining approximately 0.27 g of Tol, 0.30 g of TCE,

0.25 g of TDCE and 0.18 g of Ben and taking the

mixture to volume in 25 mL of tetraethylene glycol dimethyl ether (tetraglyme). This stock was further diluted with tetraglyme as show in Table 1 to

create specific soil VOC treatment levels for the

different experiments. All of the chemicals were

reagent-grade quality.

This method of soil subsample treatment relies

on the partial pressures of the analytes in the spiking solution to create a gaseous phase concentration to impregnate the soil grain surfaces. After

three or more days of equilibration the desiccator

was opened, and 5-mm-diameter glass beads were

placed on top of each of the ampoules, providing

temporary caps. Then, without hesitation, the ampoules were positioned in a clamp and the necks

were heat-sealed using a propane plumber’s torch.

Table 1. Fortification solutions.

Volume Volume No. of subsamples

Experiment of stock (mL) of tetraglyme (mL) fortified

Analyte concentration

A 0.1 10 6

B 0.5 9.5 6

C 2.0 8.0 6

NaHSO4 - HS/GC 0.1 10 21

NaHSO4 - PT/GC/MS 0.01 10 14

Immersion in MeOH 0.5 9.5 12

2
Table 2. Subsample sets, holding times and storage conditions.

Experiment Holding time and conditions

Analyte concentration Day 0 Day 8 Day 14

22°C† 22°C 22°C

(n=2) × 3* (n=2) × 3 (n=2) × 3

NaHSO4 - HS/GC Day 0 Day 4 Day 8 Day 14

22°C 22/4°C 22/4°C 22/4°C

(n=3) (n=3) × 2 (n=3) × 2 (n=3) × 2

NaHSO4 - PT/GC/MS Day 0 Day 5 Day 7 Day 14 Day 21

22°C 22°C 22°C 22°C 22°C

(n=3) (n=3) (n=3) (n=3) (n=2)

MeOH immersion Day 0 Day 14 Day 28 Day 42

22°C 22°C 22°C 22°C

(n=3) (n=3) (n=3) (n=3)

† Storage temperature

* Number of subsamples sacrificed for analysis

The ampoules were transferred (with their sealed

tips pointing down) to VOA vials and positioned.

Effect of analyte concentration

The first experiment assessed if the analyte concentration could inhibit the biodegradation of Ben

and Tol. Three sets (A, B, C) of six soil subsamples

were vapor-fortified to different analyte levels

(Table 1). The storage period was initiated once an

ampoule had been broken and the soil completely

dispersed into 30 mL of water contained in the

VOA vial. Breaking the ampoule and dispersing

the soil was accomplished by hand agitation. Duplicates of these soil-water subsamples were sacrificed and analyzed by HS/GC after 0, 8 and 14

days at room temperature (22°C) storage (Table 2).

Chemical preservation

with NaHSO4

HS/GC

Twenty-one soil-filled ampoules were fortified

for the holding time study of acidified subsamples

prepared for HS/GC analysis (Table 1). These 1.50-

g subsamples of the CRREL soil were acidified by

adding 0.25 g of granular NaHSO4 (pKa = 1.92) to

VOA vials containing 30 mL of Type 1 water. Both

the holding period and the acidification started

once the ampoules containing the VOC-treated soil

had been broken inside closed VOA vials with

Teflon-faced silicon septa. One set of triplicates was

analyzed on day 0, while the remaining sets were

split; half were stored at room temperature (22°C)

and half were refrigerated (4°C). A set of triplicates from each storage condition were sacrificed

and analyzed by HS/GC after holding periods of

4, 8 and 14 days (Table 2).

PT/GC/MS

Fourteen subsamples were fortified for the lowlevel PT/GC/MS holding time study (Table 1).

These 1.50-g CRREL soil subsamples were acidified by adding 0.25 g of granular NaHSO4 to VOA

vials containing 3 mL of Type 1 water. As before,

both the holding period and the acidification

started once the ampoules’ contents had been dispersed inside closed VOA vials. For this experiment the VOA vials were equipped with purgeand-trap adapter caps (Associated Design and

Manufacturing Company, Alexandria, Virginia,

Model PT-6005-0002). Four sets of triplicates and

a set of duplicates were sacrificed and analyzed

by PT/GC/MS after 0, 5, 7, 14 and 21 days of storage at 22°C (Table 2).

MeOH immersion

The MeOH immersion experiment was performed with 12 vapor-fortified soil subsamples

(Table 1). Each subsample was enclosed in a VOA

vial with a Teflon-faced silicon septum cap, then

shaken to break the ampoule and disperse the contents into 10 mL of MeOH. Sets of triplicate

subsamples were sacrificed after storage at room

temperature for periods of 0, 14, 28 and 42 days.

Unlike the other experiments, the VOA vial containing the methanolic-soil slurry was opened and

a 100-μL volume was transferred into a VOA vial

containing 30 mL of Type 1 water by piercing the

3
Table 4. Analyte concentrations (μg/g) for soil

subsamples prepared for HS/GC with 0.25 g of

NaHSO4 and stored refrigerated and at room temperatures.

Analyte Day 0 Day 4 Day 8 Day 14

NaHSO4/22°C

TDCE 4.5±0.1 4.4±0.1 4.3±0.1 4.3±0.2

Ben 8.6±0.2 8.4±0.1 8.7±0.3 8.7±0.1

TCE 9.1±0.3 8.5±0.3 8.7±0.2 8.6±0.3

Tol 13±0 12±0 13±0 13±0

NaHSO4/4°C

TDCE 4.1±0.2 4.6±0.2 4.3±0.2

Ben 7.9±0.3 9.1±0.4 8.5±0.5

TCE 8.1±0.3 9.0±0.4 8.4±0.4

Tol 12±0.6 13±0.6 13±0.6

C, which had the highest cumulative VOC concentration, showed no reductions in concentration

greater than 13% for any of the four analytes. In

contrast, the concentrations Ben and Tol decreased

by more than 90% over the 14-day holding period

in the A and B treatment batches.

Effect of acidification

Tables 4 and 5 show the results obtained for the

two holding time experiments involving subsamples chemically preserved by acidification. The

subsamples prepared for HS/GC analysis showed

no losses that exceeded 10% for any of the comTable 3. Holding time concentration (μg/g)

results for soil subsamples treated at three

different analyte levels and prepared for HS/

GC analysis.

Analyte Day 0 Day 8 Day 14

Treatment A

TDCE 0.71± 0.01 0.66± 0 0.64± 0.03

Ben 1.0± 0 0.59± 0 ND*

TCE 0.88± 0 0.78± 0.02 0.84± 0.03

Tol 2.6± 0 1.4± 0 ND

Total 5.19 3.43 1.48

Treatment B

TDCE 32± 0 32± 1 30± 1

Ben 50± 1 8.8± 4.2 ND

TCE 41± 1 36± 0 28± 2

Tol 40± 1 24± 2 3.6± 1.6

Total 163 100.8 61.6

Treatment C

TDCE 33± 1 35± 0 34± 1

Ben 65± 0 65± 4 58± 1

TCE 53± 1 55± 2 48± 1

Tol 92± 3 88± 4 82± 5

Total 243 243 222

*ND—not detected

septum. This aqueous solution was then analyzed

by HS/GC.

Analysis

Both the HS/GC and PT/GC/MS analyses of

subsamples were performed following procedures

that have been described in more detail elsewhere

(Hewitt et al. 1992). Briefly, HS/GC analysis was

performed at room temperature after shaking the

VOA vials for two minutes to obtain a headspace

equilibrium. Headspace vapors were removed

from the sealed VOA vial using a gas-tight syringe

to penetrate the Teflon-faced silicon septum. These

headspace vapors were then injected into a PhotoVac gas chromatograph (model 10S10, PhotoVac,

Inc.) equipped with a packed column containing

10% Se-30 on Chromsorb 80/100 mesh. Sample

analyte concentrations were established relative to

aqueous headspace standards. For those samples

treated by adding 0.25 g of NaHSO4, this same

amount of acid was added to the standards to compensate for the small (approximately 5%) saltingout effect.

Subsamples analyzed by PT/GC/MS followed

the general SW-846 Method 8240 guidelines for

soils containing VOCs at less than 1 μg/g (U.S.

Environmental Protection Agency 1986). These

subsamples were held in VOA vials equipped with

a special adapter so that they could be quickly attached to a purge-and-trap system. By design, this

special adapter attaches to the purge-and-trap

manifold after a Teflon ball is pushed out of an

air-tight seat, which momentarily (<1 s) creates a

circular opening (<1 mm in diameter)in the lid of

the 44-cm3 vial. Since the low-level PT/GC/MS

subsample already contained 3 mL of water, only

an additional 3 mL was used to introduce the internal standard.

RESULTS

Effect of analyte concentration

The initial (day 0) cumulative VOC concentrations for the treatment batches A, B and C were

approximately 5.2, 160 and 240 μg/g, respectively

(Table 3). After storage for 14 days at room temperature, the cumulative concentrations had decreased for these three treatment batches by 71, 61

and 8%. With the exception of one TCE value,

which is perhaps aberrant, the variations in concentrations between holding times were no greater

than 13% for the two chlorinated compounds, independent of treatment level. Similarly, treatment

4
pounds over the 14-day holding period, regardless of storage temperature. Those prepared for

low-level PT/GC/MS and stored at room temperature showed variations in analyte concentrations

up to 25%; however, no consistent trends were observed.

MeOH immersion

The results for the soil subsamples immersed

in MeOH and held at room temperature are shown

in Table 6. In this experiment there were only small

changes in the analyte concentrations for subsamples stored over a 42-day period.

Table 5. Analyte concentrations (ng/g) for soil subsamples held

at room temperature and prepared for low-level PT/GC/MS analysis.

Analyte Day 0 Day 5 Day 7 Day 14 Day 21

NaHSO4/22°C

TDCE 194±7 228±11 210±9 239±14 212±16

Ben 286±18 325±12 323±14 347±18 318±6

TCE 254±15 297±12 293±18 347±18 272±7

Tol 282±21 311±14 289±27 328±17 286±2

DISCUSSION

Since in all of these studies, the soils were fortified in an air-filled chamber and the ampoules were

opened in VOA vials with at least 14 cm3 of

headspace, the experimental conditions were aerobic. Even so, the experimental protocol successfully isolated the VOCs, allowing holding time

studies to address biodegradation in the absence

of volatilization. For example, TDCE, the analyte

with the highest vapor pressure, was remarkably

stable in concentration over periods exceeding 14

days. A similar stability in concentration was also

observed for TCE. In contrast, Ben and Tol often

underwent rapid reductions in concentration unless the subsamples were chemically preserved, a

process that has long been suspected, since these

two aromatic compounds aerobically biodegrade

Table 6. Analyte concentrations (μg/g) for soil subsamples stored immersed in 10 mL of MeOH and held

at room temperature.

Analyte Day 0 Day 14 Day 28 Day 42

MeOH/22°C

TDCE 2.6±0.1 2.7±0 2.8±0.2 2.6±0.1

Ben 4.8±0.1 4.8±0.2 4.9±0.2 5.1±0.1

TCE 4.3±0.1 4.3±0.2 4.4±0.2 4.3±0.1

Tol 11±1 11±1 12±1 11±0

a. Subsamples immersed in methanol and held at 22°C.

b. Subsamples dispersed into 30 mL of water acidified

with NaHSO4 and held at 22°C.

c. Subsample dispersed into 30 mL of water and held

at 4°C. (Hewitt 1994c).

Figure 1. Holding time results for subsamples prepared for HS/GC analysis.

(Suflita 1989). This feature is illustrated in Figures

1 and 2, which show the results for subsamples

stored with and without chemical preservation.

Figure 3 is a plot of the percent cumulative VOC

concentration relative to day 0 for the treatment

level experiment (Table 3). Also included in this

plot are the results from a previous study (Hewitt

12

8

4

0 14 28 42

Benzene

Toluene

H ldi Ti (d )

Concentration (μg/g)

2

10

6

Concentration (μg/g)

2 6 10 14

14

12

10

8

6

4

2

0

H ldi Ti (d )

g ( y)

14

12

10

8

6

4

2

0 2 6 10 14

H ldi Ti (d )

Concentration (μg/g)

5
400

200

0

3 9 15 21

Benzene

Toluene

Concentration (ng/g)

a. Subsample wetted with 3 mL of water acidified with

NaHSO4 and stored at 22°C. Concentration (ng/g)

40

2 6 10 14

Holding Time (days)

20

0

Holding Time (days)

b. Subsample moistened with 0.2 mL of water and stored

at 4°C. (From Hewitt 1994c.)

Figure 2. Holding time results for subsamples prepared for PT/GC/MS analysis.

1994c) for a set of subsamples held under similar

conditions. The only difference between these experiments was that subsamples were sacrificed upon analysis in the treatment level study, where as

previously the subsamples had been repeatedly

analyzed. In the absence of chemical preservation,

the rate of loss due to biodegradation in the CRREL

soil is fairly reproducible. This figure also indicates

that biodegradation in a given soil can be suppressed when treated with high concentrations of

these four VOCs. The cumulative VOC concentration where biodegradation appears to be inhibited

in the CRREL soil is around 240 μg/g, well above

the treatment level used in the chemical preservation studies. Therefore,we can be reasonably certain that the stability of the Ben and Tol concentrations in acidified samples and samples immersed

in MeOH is attributable solely to chemical preservation.

Even though the success of these two methods

of chemical preservation were relative to laboratory-fortified samples, field samples most likely

will behave similarly. The reasoning for this asFigure 3. Percent cumulative concentration relative

to day 0 for the treatment level soil subsample sets (A,

B, C; Table 3) and for a set (D) handled under similar

protocols (Hewitt 1994c). All subsamples were prepared

for HS/GC analysis and held at room temperature without chemical preservation.

sumption is that the chemical preservatives inhibited the activity of the microbes that were indigenous to the soil. Furthermore, since the soil

subsamples were vapor-fortified just prior to initiating the experimental conditions, the VOCs were

most likely readily available. For this reason, laboratory vapor-fortified soil samples may represent

a worst-case scenario. There are, however, some

precautions that need to be addressed. For instance, only four VOCs were tested in this study.

Moreover, when acidification is used, it is most

likely important that a pH of 2 or lower is obtained

and that the soil subsample becomes completely

dispersed once enclosed in the VOA vial.

Analyte transformations due to the MeOH or

NaHSO4 are unlikely. Methanol is commonly used

as the solvent for preparing VOC standards, and a

study performed with laboratory water, surface

water and groundwater treated with 25 VOCs and

acidified with NaHSO4 showed no chemical interferences (Maskarinec et al. 1990).

Not included in this report are the results from

an experiment using NaHSO4 to acidify subsam100

80

60

40

20

0 2 4 6 8 10 12 14

Holding Time (days)

C

D

A B

Percent Cumulative Total Concentration

Relative to Day Zero

6
ples prepared for HS/GC analysis, which failed

to prevent the loss of Ben and Tol. The reason for

not including this experiment is that an artifact was

detected. Close inspection of the treated soil

subsamples established that some had not been

completely dispersed at the start of the storage

period. These subsamples, which contained

clumps of wetted soil trapped in partially broken

ampoules, showed losses of Ben and Tol, while

there were no detectable losses of these two

analytes in subsamples where dispersion was complete. Because of this artifact the experiment was

repeated, taking special care to completely disperse

the soil in the acidified water. The results of this

second experiment found that there were no

changes in any of the analyte concentrations

greater than 10% (Table 4). Thus, depending on

the soil texture and composition, field subsamples

may require vortex or sonication mixing. In addition, more than 3 mL of water may be necessary

when preparing for low-level PT/GC/MS. Also,

since the buffering capacity of soils varies widely,

the amount of NaHSO4 necessary to achieve a pH

of 2 should be evaluated on a case-by-case basis.

Lastly, when high levels of calcium carbonate are

present in the soil acidification may not be feasible.

The selection of subsample preservation by either acidification or immersion in MeOH depends

on the VOC concentrations expected and the

method of analysis. The two methods of analysis

used here were HS/GC and PT/GC/MS. The

former is very compatible with on-site operations,

while the latter is often required for fixed (off-site)

laboratories involved with government-regulated

site investigations. Acidification with NaHSO4 is

compatible with low levels of VOC (<1 μg/g),

while immersion in MeOH is preferable with high

levels (>1 μg/g).

By using chemical preservation with sample

collection protocols that minimize volatilization

losses during storage and analysis, environmentally representative analyte concentrations are more

apt to remain stable for 14 days (Hewitt et al., in

press). Some small VOC losses may occur independent of acidification since Teflon (the septum

cap liner) is believed to sorb VOCs (Leggett and

Parker 1994). Another advantage that could be

gained by using chemical preservation is that refrigeration would not be as critical. Relaxing this

requirement would lower the cost of both on-site

operations and shipping. Furthermore, the results

(Tables 5 and 6) show that the concentration stability obtained by either acidification or immersion in MeOH may permit holding times to be increased beyond 14 days. Increasing holding times

would not only be beneficial to site investigations

performed in remote locations where turn-around

limits are hard to achieve, but may also allow some

samples to be archived.

CONCLUSION

Chemical preservation can maintain stable concentrations of Ben and Tol in soil subsamples that

exhibited biodegradation of these two compounds

when held for 14 days at 4°C. Concentrations of

TDCE and TCE were stable with and without preservation. The two methods of chemical preservation used—immersion in MeOH and acidification

with NaHSO4—are compatible with subsamples

collected and handled for both PT/GC/MS and

HS/GC analysis. Prior to performing chemical

preservation studies, the range where biodegradation is uninhibited by analyte concentration

must be established.

LITERATURE CITED

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methods for trichloroethylene in vadose zone soils.

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Hewitt, A.D. (1994b) Losses of trichloroethylene

for soil during sample collection, storage and laboratory handling. USA Cold Regions Research and

Engineering Laboratory, Special Report 94-8.

Hewitt, A.D. (1994c) Concentration stability of

four volatile organic compounds in soil subsamples. USA Cold Regions Research and Engineering Laboratory, Special Report 94-6.

Hewitt, A.D. (1994d) Vapor-fortified QA/QC soil

subsamples for the analysis of volatile organic

compounds. American Environmental Laboratory,

March.

Hewitt, A.D. (1994e) Preparation of spiked soils

by vapor fortification for volatile organic compound analysis. Journal of the Association of Official

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Hewitt, A.D., T.F. Jenkins and C.L. Grant (in press)

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Research Needs, Las Vegas, Nevada, January 12–14,

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February 1995

Chemical Preservation of Volatile Organic Compounds in Soil

Subsamples

Alan D. Hewitt

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 95-5

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland 21010-5401 SFIM-AEC-ET-CR-95007

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

14

Chemical preservation Soil sampling

Hazardous waste Volatile organic compounds

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

This study evaluated chemical preservation as a means of inhibiting the biological degradation of volatile organic

compounds (VOCs) in soil subsamples held for 14 days or longer. Experiments were performed using a soil in

which benzene and toluene were found to rapidly biodegrade under aerobic conditions while following

protocols consistent with high-level (VOCs at >1 μg/g) and low-level (VOCs at <1 μg/g) purge-and-trap gas

chromatography mass spectrometry and static headspace gas chromatography analysis. Chemical preservation

consisted of immersing soil subsamples fortified with trans-1,2-dichloroethylene (TDCE), trichloroethylene

(TCE), benzene and toluene in methanol or water acidified to a pH of less than 2 with NaHSO4. These two methods

of chemical preservation resulted in stable concentrations of these two aromatic hydrocarbons even when held

at room temperature. The two chlorinated hydrocarbons showed stable concentrations with and without

chemical preservation. This result, in conjunction with earlier findings, suggests that chemical preservation is

more effective at suppressing biodegradation than the current practice of refrigeration (4°C).