SPECIAL REPORT 95-26

Enhanced Preservation of

Volatile Organic Compounds in

Soil With Sodium Bisulfate

Alan D. Hewitt November 1995
Abstract

Sodium bisulfate (NaHSO4) was evaluated as a means of chemically preserving soil samples to prevent the microbiological degradation of volatile

organic compounds (VOCs). Laboratory sample treatment consisted of spiking

soil samples held in glass ampoules with aqueous solutions containing

eight different VOCs or gasoline and then sealing them to eliminate volatilization as a concern. Samples preserved with NaHSO4 were held at room

temperature (22°C), while equal numbers of unpreserved samples were

stored refrigerated (4°C) and at room temperature. Results show that concentrations of all of the halogenated hydrocarbons tested (14) remain fairly

constant, independent of temperature or preservation. In contrast, all the

aromatic hydrocarbons (10) tested as separate analytes, or ones that could

easily be identified in gasoline, experienced a complete (>95%) loss when

held for nine days at room temperature. Refrigeration reduced the rate of

biodegradation, but two aromatic hydrocarbons showed substantial losses

(>80%) within the currently recommended 14-day holding period. Over a

28-day refrigerated period, reductions of greater than 95% occurred for 9

of 10 aromatic hydrocarbons tested. With the exception of styrene, chemical preservation by introducing NaHSO4 mitigated the loss of all of aromatic hydrocarbons tested over a 28-day holding period when samples

were stored at room temperature. Therefore, NaHSO4 preservation is one

way of effectively eliminating biodegradation of VOCs in soil samples intended for low level (<1-μg/g) analysis.

For conversion of SI units to non-SI units of measurement consult ASTM

Standard E380-93, 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 95-26

Enhanced Preservation of

Volatile Organic Compounds in

Soil With Sodium Bisulfate

Alan D. Hewitt November 1995

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

SFIM-AEC-ET-CR-95081

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 Division, Research and Engineering Directorate, 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 Dr. C.L. Grant and L.V. Parker for critical

review of the text.

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 of 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
CONTENTS

Page

Preface ................................................................................................................................. ii

Introduction........................................................................................................................ 1

Experimental section......................................................................................................... 1

Analysis............................................................................................................................... 3

Results and discussion ..................................................................................................... 5

Conclusion .......................................................................................................................... 14

Literature cited ................................................................................................................... 14

Abstract ............................................................................................................................... 17

ILLUSTRATIONS

Figure

1. Gasoline-contaminated soil stored at 22°C .......................................................... 4

2. Gasoline-contaminated soil stored at 4°C ............................................................ 4

3. Gasoline-contaminated soil preserved with NaHSO4 and stored at 22°C ..... 4

4. Set 1/trial 1. Contaminated soil stored at 22°C .................................................. 10

5. Set 1/trial 1. Contaminated soil stored at 4°C .................................................... 10

6. Set 1/trial 1. Contaminated soil preserved with NaHSO4 and stored

at 22°C ................................................................................................................... 10

7. Set 1/trial 4. Contaminated soil stored at 22°C .................................................. 10

8. Set 1/trial 4. Contaminated soil stored at 4°C .................................................... 11

9. Set 1/trial 4. Contaminated soil preserved with NaHSO4 and stored

at 22°C ................................................................................................................... 11

10. Set 2/trial 2. Contaminated soil stored at 22°C .................................................. 11

11. Set 3/trial 3. Contaminated soil stored at 22°C .................................................. 11

12. Set 2/trial 2. Contaminated soil stored at 4°C .................................................... 12

13. Set 3/trial 3. Contaminated soil stored at 4°C .................................................... 12

14. Set 2/trial 2. Contaminated soil preserved with NaHSO4 and stored

at 22°C ................................................................................................................... 12

15. Set 3/trial 3. Contaminated soil preserved with NaHSO4 and stored

at 22°C ................................................................................................................... 12

16. Aqueous solution of set 1 analytes preserved with NaHSO4 and stored

at 4°C ..................................................................................................................... 13

TABLES

Table

1. Volatile organic compounds and petroleum products studied during

holding time and chemical preservation experiments ................................. 2

iii
Table Page

2. Sampling holding and storage conditions ........................................................... 3

3. Set 1, trial 1. Mean and standard deviations of triplicate analyte

concentrations of spiking solution and of analyte concentrations for

preserved and unpreserved samples stored at 22° and 4°C ........................ 5

4. Set 2, trial 2. Mean and standard deviations of triplicate analyte

concentrations of spiking solution and of analyte concentrations for

preserved and unpreserved samples stored at 22° and 4°C ........................ 6

5. Set 3, trial 3. Mean and standard deviations of triplicate analyte

concentrations of spiking solution and of analyte concentrations for

preserved and unpreserved samples stored at 22° and 4°C ........................ 7

6. Set 1, trial 4. Mean and standard deviations of triplicate analyte

concentrations of spiking solution after 2 and 30 days of refrigerated

storage, and for analyte concentrations in preserved and unpreserved

 samples stored at 22° and 4°C.......................................................................... 8

7. Set 4, trial 5. Mean and standard deviations of triplicate gasoline

concentrations of spiking solution after 1 day of refrigerated storage,

and for gasoline concentrations in preserved and unpreserved

samples stored at 22° and 4°C ........................................................................... 9

8. Response relative to fresh standard of solutions preserved with NaHSO4

and held refrigerated in either an upright or inverted position ................. 13

iv
INTRODUCTION

Most soil samples collected during site investigations for establishing the presence and concentration of volatile compounds (VOCs) are sent to

off-site laboratories for analysis. To allow for some

flexibility between sampling and analysis operations, the U.S. Environmental Protection Agency

(U.S. EPA 1986) has recommended that samples

be stored at 4°C, and held no more than 14 days.

This practice continues although it is well-recognized that soils can remain biologically active under these conditions. While several efforts have

been made to demonstrate the magnitude of this

potential problem (Jackson et al. 1991, Maskarinec et al. 1992 King 1993), only recently have studies been designed to eliminate confounding of

biodegradation and volatilization losses (Hewitt

1994, Hewitt 1995a,b, Turriff 1995). These efforts

are the first to assess only the biological influence

on VOCs in soil samples held at 4°C.

Our approach has been to seal treated samples

in glass ampoules before exposing them to various holding and storage conditions (Hewitt 1994,

Hewitt 1995 a,b). Here we assess the concentration stability of 24 (see Table 1) of the 56 analytes

currently identified by the Environmental Protection Agency as hazardous VOCs (U.S. EPA 1986,

SW-846, Methods 8240/8260), and gasoline. Experiments look at both the effect of chemical preservation and temperature on analyte concentration in soil samples held over a 28-day storage

period under conditions that eliminated volatilization losses. The preservative chosen was sodium bisulfate (NaHSO4). A sufficient quantity of

this salt was used so that pH 2 or less was obtained, once the soil sample was made into an

aqueous slurry. The selection of this chemical preservative was based on its low toxicity, compatibility with field operations, and its success in a

study of VOC stability in aqueous matrices

(Maskarinec 1990). The 28-day storage period was

selected based on the success of an earlier study

(Hewitt 1995) and efforts to establish longer proven holding times for VOCs in preserved aqueous

matrices.*

Here, spiked soil samples were stored in sealed

glass ampoules, and analyzed after transfer to

volatile organic analysis (VOA) vials containing

water. Once VOA vials were capped, the ampoules

were broken, dispersing the contents in preparation for static headspace gas chromatography

(HS/GC) analysis. Using this protocol, we never

exposed the spiked soils to the atmosphere, allowing biodegradation and chemical preservation

studies to be performed independent of volatilization. This experimental procedure is consistent

with practice of retaining soil samples in either

vaportight glass bottles while they await laboratory subsampling and analysis (this practice is

not recommended by the author [Hewitt et al.

1995]), or in VOA vials for low level purge and

trap gas chromatography mass spectrometry

(PT/GC/MS) analysis as recommended in Method

5035, a method scheduled for inclusion in the proposed third update of the SW-846, U.S. EPA (1986).

EXPERIMENTAL SECTION

The silty-sand topsoil used in this study was

obtained locally from between 5 and 10 cm below

the ground surface just before the start of this

Enhanced Preservation of

Volatile Organic Compounds

in Soil with Sodium Bisulfate

ALAN D. HEWITT

* Personal communication with David Bottrell, U.S.

Department of Energy, Washington, D.C., 1995.
neat (reagent grade) VOCs or unleaded gasoline

to a 100-mL volumetric flask containing about

102 mL of groundwater. The quantities of the neat

analytes added would have created an aqueous

concentration of approximately 50 mg/L, if dissolution were complete. However, this is unlikely

based on their solubilities. After adding either

eight analytes or gasoline, the solution was manually shaken; then a Teflon stirring bar was introduced and the flask topped off with water, leaving less than 0.5 mL of headspace. These solutions

were stirred for at least 24 hours and then allowed to sit undisturbed for 1 hour prior to removing aliquots.

Each soil sample was spiked with a 200-μL aliquot from the prepared aqueous solution by using a 500-μL glass syringe (Hamilton). To avoid

undissolved low density analytes that would acTable 1. Volatile organic compounds and petroleum products studied

during holding time and chemical preservation experiments.

Solubility o/w† Vol.††

Abbrev.* (mg/L) Log P (μL) CAS

Set 1

Benzene Ben 1780 2.13 5.7 71-43-2

Toluene Tol 515 2.65 5.8 108-88-3

Ethylbenzene E-Ben 152 3.13 5.8 100-41-4

p-Xylene p-Xyl 200 3.18 5.8 106-42-34

o-Xylene o-Xyl 152 2.95 5.7 95-47-6

trans-1,2-Dichloroethene TDCE 600 2.09 3.5 156-60-5

Trichloroethene TCE 1100 2.53 3.7 79-01-6

Tetrachloroethene PCE 150 2.60 3.1 127-18-4

Set 2

m-Xylene m-Xyl 173 3.20 5.8 108-38-3

Methylene chloride MC 20,000 1.30 3.8 75-09-2

1,1-Dichloroethane 1,1 DCA 5500 1.78 4.1 75-34-3

Chloroform CF 8000 1.97 3.4 67-66-3

1,2-Dichloroethane 1,2 DCA 8690 1.48 4.0 107-06-2

Bromodichloromethane BDCM 4500 1.88 2.5 75-27-4

1,1,2-Trichloroethane 1,1,2 TCA 4500 2.18 3.5 79-00-5

Chlorobenzene CB 500 2.84 4.5 108-90-7

Set 3:

Styrene Styrene 300 2.95 5.5 100-42-5

Isopropylbenzene iso-PB 50 3.66 5.8 98-82-8

n-Propybenzene n-PB 55 3.57 5.8 103-65-1

n-Butyl benzene n-BB 11.8 4.29 5.7 104-51-8

Carbon tetrachloride C-tet 800 2.83 3.1 56-23-5

1,3-Dichlorobenzene 1,3 DCB 69 3.38 3.9 541-73-1

cis-1,2-Dichloroethene CDCE ? ? 3.9 ?

1,2-Dichloropropane 1,2 DCP 2700 2.28 4.3 78-87-5

Set 4:

Gasoline Gas 95

* Abbreviation.

† Octanol–water partition coefficient.

†† Volume.

experiment. It was air–dried for 24 hours, reducing the moisture content (weight percent relative

to dried soil) from 24 to 4.3% (ASTM D2216-66)

passed through a 30-mesh sieve, and thoroughly

mixed. The organic carbon content was 0.94±0.04%

(Hach method 8097). Subsamples of 1.00±0.01 g

were transferred to 2-mL glass ampoules (Wheaton, actual vol. ≈ 3.1 mL) some of which already

contained 0.25 g of NaHSO4 as a chemical preservative (Table 2). Sodium bisulfate has a pKa of

1.92, and the quantity used created a pH of about

1.9, once sufficient water was added to produce a

slurry condition. For the series of experiments

described here, 15 ampoules contained both NaHSO4 and moist soil, and 27 contained just moist

soil.

The fortification solution was prepared by separately adding microliter volumes (Table 1) of eight

2
Teflon-faced butyl rubber septum (Wheaton). One

of these samples was prepared at the beginning,

middle and end of the soil sample spiking process to estimate spiking solution concentration

and homogeneity. It took approximately 1 hr to

spike and seal the 42 soil samples, after which

each one was hand shaken, mixing their contents.

The first, middle, and last spiked soil samples,

with and without NaHSO4, were selected for the

initial analysis. For trials 1 through 3, the initial

analysis was performed on the day of treatment

(day 0). However, there was a 24-hr or greater

period of refrigerated equilibration between spiking and the initial analysis for trials 4 and 5. After

the initial analysis, 12 sealed ampoules containing only fortified soil remained refrigerated (4°C);

all of the other subsamples were held at room

temperature (22°C). Triplicates from these three

subsample sets (22°C preserved and unpreserved,

4°C unpreserved) were selected at random and

analyzed after various storage periods up to 28

days. The samples in ampoules were prepared for

analysis by placing them in auto sampler vials (22

mL) that contained 14 mL of type 1 water (MilliQ,

Millipore Corp.). After sealing with a crimp-top

cap, each vial was vigorously hand shaken, causing the ampoule to break and allowing the treated soil to be completely dispersed. To facilitate an

HS equilibration condition, shaking continued for

another two minutes after the ampoule was broken, and prior to placing in the auto sampler for

analysis. Table 2 describes the holding and storage conditions for each of the five trials covered

in this study.

ANALYSIS

All samples were analyzed with a headspace

auto sampler (Tekmar 7000), coupled to a GC (SRI,

model 8610-0058) equipped with a 15-m DB1 0.53

capillary column. The auto sampler parameters

were 1) platen temperature 25°C and equilibration time 20 min., 2) loop size 1 mL, 3) loop and

line temperature 100°C, 4) pressurization time 0.20

min., 5) pressurization equilibration time 0.10 min.,

6) loop fill time 0.25 min., 7) loop equilibration

time 0.10 min., 8) inject time 1.0 min. and 9) vial

pressurization 7.5 psi. The HS sample was transferred to the GC for separation and flame ionization detection (FID). For the first two sets of analytes (set 1 and 2), the GC temperature sequence

started with the injection, stayed at 40°C for 1

min., then increased to 100°C in 6 min., and was

Table 2. Sample holding and storage conditions.

For each trial, 27 ampoules contained soil and 15

contained soil and 0.25 g NaHSO4, prior to spiking.

Set 1,trial 1

Day 0

Spiked: 42 soil subsamples.

Stored: 12 soil samples refrigerated (4°C), 30 held at 22°C.

Analyzed: 3 VOA vials, 3 soil samples, 3 soil samples preserved with NaHSO4.

Day 5, 9, 14, 21

Analyzed: 3 samples stored at 4°C, 3 samples stored at 22°C,

3 samples preserved with NaHSO4.

Set 2, trial 2

Day 0 (same as set 1, trial 1 )

Day 4, 8, 14, 28 (same as set 1, trial 1 )

Set 3, trial 3

Day 0 (same as set 1, trial 1 )

Day 3, 6, 13, 28 (same as aet 1, trial 1 )

Set 1, trial 4

Day -2

Spiked: 42 soil samples

Day 0 (after two days storage at 4°C).

Stored: 12 soil samples remained refrigerated (4°C), 30 held

at 22°C.

Analyzed: 3 VOA vials, 3 soil samples, 3 soil samples preserved with NaHSO4.

Day 1 , 2, 3, 5

Analyzed: 3 samples stored at 22°C

Day 5, 13, 21, 28

Analyzed: 3 samples stored at 4°C, 3 samples preserved with

NaHSO4.

Set 4, trial 5

Day -1

Spiked: 42 soil samples

Day 0 (after one day storage at 4°C). (same as set 1, trial 4)

Day 5, 10, 14, 28 (same as set 1, trial 1 )

cumulate at the surface, aliquots were taken well

below the water/air interface, and the stainless

steel needle was wiped prior to inserting into the

ampoule’s neck. Before transferring a spike, each

ampoule was placed in a metal tension clamp so

it could be heat-sealed with a propane torch immediately after spiking. Once sealed, every ampoule contained 1 g of soil and the moisture content had been returned to 24%. In addition to

preparing the soil samples, a 200-μL aliquot of the

spiking solution was placed into each of three

auto sampler headspace vials (22 mL, Tekmar)

containing 15 mL of type 1 water. Each vial was

immediately capped with a crimp-top cap and

3
22 °C

D0

Ben

Tol

E-Ben/p-Xyl o-Xyl

22 °C

D5

Ben

Tol

E-Ben/p-Xyl o-Xyl

22 °C

D28

Ben

Tol

E-Ben/p-Xyl o-Xyl

22 °C

D14

Ben

Tol

E-Ben/p-Xyl o-Xyl

4 °C

D5

Ben

Tol

E-Ben/p-Xyl o-Xyl

4 °C

D0

Ben

Tol

E-Ben/p-Xyl o-Xyl

4 °C

D28

Ben

Tol

E-Ben/p-Xyl o-Xyl

4 °C

D14

Ben

Tol

E-Ben/p-Xyl

o-Xyl

Figure 2. Gasoline-contaminated soil stored

at 4°C.

Figure 1. Gasoline-contaminated soil stored

at 22°C.

Figure 3. Gasoline-contaminated soil preserved with NaHSO4 and stored at 22°C.

Ben

Tol

E-Ben/p-Xyl

o-Xyl NaHSO

D0 4

Ben

Tol

E-Ben/p-Xyl o-Xyl NaHSO

D5 4

Ben

Tol

E-Ben/p-Xyl o-Xyl NaHSO

D14 4

Ben

Tol

E-Ben/p-Xyl o-Xyl NaHSO

D28 4

4
held at 100°C for an additional 3.5 min. The third

set of analytes used a GC program consisting of

holding at 40°C for 1 min., then increasing to 150°C

in 6.1 min., and holding at 150°C for an additional

3.39 min. For gasoline the following GC program

was used: holding at 40°C for 1 min., and then

increasing to 220°C in 8 min. Using these parameters we resolved all of the analytes in the sets 1

through 3 with the exception of E-Ben and p-Xyl

(set 1). Examples of HS chromatogram for the

gasoline treated soil sample (set 4) are shown in

Figures 1 through 3. These chromatograms show

that several aromatic compounds in gasoline could

be readily identified.

Analyte concentrations were established relative

to aqueous headspace standards prepared by

adding small (<10 μL) quantities of a methanol

(MeOH) stock solution to auto sampler vials

containing 15 mL of type 1 water (Hewitt et al.

1992). For the analytes in sets 1 through 3 individual integrated peak areas or peak heights

were used, while the entire chromatogram was

integrated for gasoline (set 4).

RESULTS AND DISCUSSION

The concentration estimates of the individual analytes or of gasoline in the spiking solution, and in the preserved and unpreserved

soil samples throughout the 28-day holding

period, appear in Tables 3 through 7. The relative standard deviations (RSD) of the analyte concentrations obtained for the three

aqueous aliquots representing the spiking solution, and those of the soil samples analyzed

on day 0 ranged from less than 1% to 30%.

The worst case was for n-butyl benzene (nBB), which has a solubility of only 11.8 mg/L,

and correspondingly resulted in the lowest

treatment concentration. With the exception

of this compound, the RSDs were less than

14% and averaged less than 5%, thus demonstrating that the treatment procedure was

precise.

Inspection of the initial concentrations for

both the unpreserved and preserved soil samples shows that they often varied from the

spiking solution. The range in percentage relative differences extended from less than 1%

to 68%, with concentrations both greater and

less than that of the spiking solution (Tables

3–7). The worst case was for styrene in the

preserved soil samples. The dramatic loss of

this compound was unique to only those samples that had been treated with NaHSO4. This

issue will be addressed later. Of almost equal magnitude, n-BB was some 65% lower than expected.

This compound, which had the poorest solubility,

also has the greatest octanol–water partition (o/w)

coefficient (Table 1). Correspondingly, the other

analytes with large o/w coefficients also showed

poor spike concentration recovery from the soil

samples.

One apparent trend when using this treatment

process and analysis by HS/GC is that, as the o/w

partition coefficients increase, so does the discrepancy between the spiking solution and initial soil

sample concentrations. An additional observation

relative to the spiking solution concentrations was

Table 3. Set 1, trial 1. Mean and standard deviations of

triplicate analyte concentrations of spiking solution (μg)

and of analyte concentrations (μg/g) for preserved and

unpreserved samples stored at 22° and 4°C.

Treatment aliquot Treatment aliquot

Analyte (μg) Analyte (μg)

TDCE 10±0.3 PCE 9.6±0.3

Ben 7.0±0.3 E-Ben 7.8±0.1

TCE 13±0.3 p-Xyl 8.2±0.1

Tol 8.5±0.2 o-Xyl 8.2±0.1

Storage period

Analyte Day 0† Day 5 Day 9 Day 14 Day 21

A. 22°C—unpreserved (μg/g)

TDCE 9.5±0.3 9.7±0 9.3±0.1 8.7±0.1 9.3±0.3

Ben 6.6±0.1 ND* ND ND ND

TCE 12±0.3 11±0.2 11±0.6 9.6±0.1 10±0.2

Tol 8.0±0.0 ND ND ND ND

PCE 8.2±0.2 7.2±0.4 6.9±0.6 6.3±0.1 6.8±0.1

E-Ben 7.0±0.3 ND ND ND ND

p-Xyl 7.1±0.3 0.15±0.03 ND ND ND

o-Xyl 7.3±0.6 5.5±0.3 ND ND ND

B. 4°C—unpreserved (μg/g)

TDCE 9.5±0.3 9.4±0.3 9.6±0.2 10±0.4 9.4±0.4

Ben 6.6±0.1 6.5±0.2 5.7±0.9 1.2±1.4 ND

TCE 12±0.3 12±0.2 12±0. 1 12±0.4 11±0.4

Tol 8.0±0.0 7.6±0.1 7.6±0.2 7.1±0.5 4.4±0.4

PCE 8.2±0.2 7.5±0.1 7.5±0.2 8.0+0.3 7.4±0.2

E-Ben 7.0±0.3 6.4±0.1 6.3±0.1 6.1±0.2 5.7±0.2

p-Xyl 7.1±0.3 6.5±0.1 6.2±0.2 6.0±0.3 4.6±0.4

o-Xyl 7.3±0.6 6.7±0.1 6.6±0.2 6.5±0.2 6.6±0.2

C. 22°C—preserved with NaHSO4 (μg/g)

TDCE 11±0.4 11±0.2 10±0.2 9.5±0.2 10±0.3

Ben 7.5±0.2 7.4±0.1 7.4±0.2 6.5±0.1 7.3±0.2

TCE 14±0.4 13±0.4 13±1.0 11±0. 1 13±0.6

Tol 9.1±0.2 8.6±0.3 8.6±0.3 7.4±0.1 8.5±0.3

PCE 8.7±0.5 8.0±0.3 7.8±0.2 7.3±0.1 7.6±0.4

E-Ben 7.7±0.4 6.9±0.3 6.9±0.2 5.9±0.2 6.7±0.2

p-Xyl 7.7±0.2 7.0±0.2 6.9±0.2 6.1±0.2 6.6±0.5

o-Xyl 7.9±0.2 7.1±0.4 7.2±0.3 6.2±0.2 6.9±0.4

* ND = not detected, less than 0.02 μg of VOC/g.

† Same set used for day 0 values for unpreserved samples.

5
Table 4. Set 2, trial 2. Mean and standard deviations of

triplicate analyte concentrations of spiking solution (μg)

and of analyte concentrations (μg/g) for preserved and unpreserved samples stored at 22° and 4°C.

Treatment aliquot Treatment aliquot

Analyte (μg) Analyte (μg)

MC 11±0.3 BDCM 16±0.5

1,1 DCA 12±0.4 1,1,2 TCA 16±0.5

CF 12±0.4 CB 9.9±0.4

1,2 DCA 13±0.5 m-Xyl 12±0.6

Storage period

Analyte Day 0† Day 4 Day 8 Day 14 Day 28

A. 22°C—unpreserved (μg/g)

MC 12±0.5 11±0.3 11±0.4 10±0.2 11±0.4

1,1 DCA 12±0.3 12±0.3 12±0.4 11±0.2 12±0.4

CF 12±0.4 12±0.4 12±0.4 11±0.2 11±0.3

1,2 DCA 13±0.5 12±0.4 12±0.2 10±0.2 10±0.1

BDCM 16±0.3 15±1.0 14±0.0 14±0.3 14±0.2

1,1,2TCA 16±0.2 14±0.5 13±0.6 13±0.5 14±0.3

CB 8.7±0.3 8.3±0.3 7.8±0.3 7.5±0.2 7.4±0.1

m-Xyl 10±0.5 ND ND ND ND

B. 4°C—unpreserved (μg/g)

MC 12±0.5 11±0.2 11±0.2 11±0.5 11±0.2

1,1 DCA 12±0.3 12±0.4 12±0.3 11±0.5 12±0.1

CF 12±0.4 12±0.2 12±0.1 11±0.5 11±0.1

1,2 DCA 13±0.5 12±0.3 12±0.2 12±0.4 12±0.2

BDCM 16±0.3 14±0.3 15±0.4 14±0.9 12±0.2

1,1,2 TCA 16±0.2 14±0.5 14±0.4 14±0.4 14±0.4

CB 8.7±0.3 8.1±0.2 8.0±0.2 7.6±0.2 8.2±0.1

m-Xyl 10±0.5 9.3±0.3 9.1±0.2 0.40±0.50 ND

C. 22°C—preserved with NaHSO4 (μg/g)

MC 12±0.4 12±0.2 12±0.4 13±0.1 13±0.1

1,1 DCA 14±0.6 13±0.3 13±0.4 12±0.1 13±0.1

CF 13±0.5 13±0.2 13±0.3 12±0.2 13±0.2

1,2 DCA 14±0.3 14±0.1 14±0.4 13±0.3 13±0.1

BDCM 17±0.2 17±0.4 17±0.9 16±0.5 17±0.5

1,1,2 TCA 16±0.5 16±0.2 15±0.3 15±0.6 16±0.8

CB 9.4±0.4 8.4±0.1 8.1±0.3 7.5±0.2 7.7±0.1

m-Xyl 11±0.4 9.9±0.3 9.3±04 8.7±0.3 9.3±0.2

* ND = not detected, less than 0.02 μg of VOC/g. † Same set used for day 0 values for unpreserved samples.

that the analytes with o/w partition coefficients

of less than 2.6 had concentrations in the preserved soil samples that were consistently greater

than the spiking solution. These two findings are

consistent with analyte–organic carbon partition

phenomena (Chiou 1989) and salting out (Ioffe

and Vitenberg 1982). Briefly, the greater the octanol–water partition (o/w) coefficient the greater the tendency for an organic compound to partition with the organic matter present in a given

soil, while salting out affects the solubility of a

VOC. Since the differences in concentrations between the spiking solution and that of the preserved samples were products of both organic

matter partitioning and salting out, these changes

could not be compensated simply by matching

the solution matrix between samples and standards (i.e., using matrix modifiers). Despite these

trends, the sample treatment precision and the

levels established for the analytes in the soil samples were adequate for assessing VOC concentration stability.

Consistent with previous studies where samples were held in either sealed glass ampoules or

capped VOA vials (Hewitt 1994, Hewitt 1995a,b),

only small decreases were observed (<35%) for

the chlorinated compound concentrations. This

trend was fairly independent of storage condition

or preservation, and was believed to be caused by

slow soil sorption (Chiou 1989). To support this

6
Table 5. Set 3, trial 3. Mean and standard deviations of triplicate

analyte concentrations of spiking solution (μg) and of analyte

concentrations (μg/g) for preserved and unpreserved samples

stored at 22° and 4°C.

Treatment aliquot Treatment aliquot

Analyte (μg) Analyte (μg)

CDCE 12±0.7 iso-PB 3.4±0.2

C-tet 8.9±0.1 n-PB 2.8±0.2

1,2 DCP 13±0.3 1,3 DCB 4.4±0.1

Styrene 7.4±1.0 n-BB 0.81±0.21

Storage period

Analyte Day 0† Day 3 Day 6 Day 13 Day 28

A. 22°C—unpreserved (μg/g)

CDCE 11±0.4 11±0.6 9.7±0.7 7.7±1.0 7.2±0.3

C-tet 8.2±0.4 7.9±0.5 7.3±0.7 6.8±1.0 6.1±1.5

1,2 DCP 12±0.4 12±0.6 12±0.3 9.1±0.6 10±0.5

Styrene 5.9±0.2 ND ND ND ND

iso-PB 2.4±0.2 0.07±0.07 ND ND ND

n-PB 1.7±0.2 0.04±0.03 ND ND ND

1,3 DCB 2.7±0.1 2.1±0.2 2.1±0.1 1.6±0.1 1.9±0.1

n-BB 0.30±0.09 0.03±0.02 ND ND ND

B. 4°C—unpreserved (μg/g)

CDCE 11±0.4 11±0.2 11±0.5 11±0.3 11±0.2

C-tet 8.2±0.4 7.8±0.5 8.0±0.1 8.0±0.2 7.8±0.6

1,2 DCP 12±0.4 12±0.2 12±0..2 12±0.4 13±0.3

Styrene 5.9±0.2 5.3±0.1 5.5±0.1 4.6±0.1 ND

iso-PB 2.4±0.2 2.1±0.1 2.1±0.1 1.9±0.1 ND

n-PB 1.7±0.2 1.4±0.1 1.5±0.1 1.2±0.1 ND

1,3 DCB 2.7±0.1 2.3±0.1 2.4±0.1 2.3±0.1 2.4±0.1

n-BB 0.30±0.09 0.21±0.01 0.23±0.01 0.16±0.01 0.02±0.02

C. 22°C—preserved with NaHSO4 (μg/g)

CDCE 13±0.4 13±0.6 12±0.5 12±0.4 12±0.2

C-tet 8.8±0.2 8.5±0.3 8.4±0.3 8.4±0.6 8.5±0.2

1,2 DCP 14±0.1 14±0.6 14±0.3 13±0.2 14±0.6

Styrene 2.4±0.8 0.50±0.12 0.57±0.10 0.33±0.12 0.12±0.12

iso-PB 2.5±0.1 2.2±0.3 2.3±0.1 2.2±0.1 2.1±0.1

n-PB 1.8±0.1 1.5±0.2 1.6±0.1 1.5±0.1 1.4±0.1

1,3 DCB 2.6±0.1 2.2±0.3 2.2±0.1 2.1±0.1 2.0±0.1

n-BB 0.28±0.04 0.22±0.03 0.22±0.01 0.23±0.01 0.20±0.01

* ND = not detected, less than 0.02 μg of VOC/g † Same set used for day 0 values for unpreserved samples.

theory, a second experiment with the set 1 analytes was performed, but a two-day period of

refrigerated (4°C) storage was allowed between

treatment and the initial analysis. This additional

holding period allowed the analytes to equilibrate

(sorb) with the organic carbon present in the soil.

Comparing Tables 3 and 6 (Fig. 4–6 vs. 7–9) shows

that while there is often a decreasing trend of the

trichloroethylene (TCE) and perchloroethylene

(PCE) concentrations in trial 1, this did not occur

in trial 4. Based on this finding, the decreases in

analyte concentrations for the chlorinated compounds in trials 1 through 3 can be partly attributed

to slow sorption by the organic matter in soil.

This process is not readily reversed by aqueous extraction in preparation for static HS/GC

analysis. Losses of similar magnitude (<35%) may

also have occurred for the aromatic hydrocarbons

in these first three trials.

All of the soil samples prepared in this study

had a moisture content of 24% after treatment and

were exposed to approximately 2.5 cm3 of air during storage in the 2-mL glass ampoules. This moisture and oxygen content is sufficient to allow for

the aerobic microbial degradation of the VOCs

(Atlas 1981). Correspondingly, the soil subsamples held at room temperature (22°C), showed a

complete (>95%) loss of the aromatic hydrocarbons

within nine days (Fig. 4, 10 and 11). Indeed, among

the analytes in the first three sets, with the excep7
Table 6. Set 1, trial 4. Mean and standard deviations of triplicate analyte concentrations of spiking solution (μg) after 2

and 30 days of refrigerated storage, and for analyte concentrations (μg/g) in preserved and unpreserved samples stored

at 22° and 4°C.

Treatment aliquot Treatment aliquot

Day 2 Day 30 Day 2 Day 30

Analyte (μg) (μg) Analyte (μg) (μg)

TDCE 5.4±0.1 5.1±0.2 PCE 9.0±0.2 7.9±0.2

Ben 11±0.2 11±0.3 E-Ben 9.9±0.3 9.0±0.2

TCE 12±0.2 11±0.2 p-Xyl 9.2±0.1 8.6±0.2

Tol 10±0.2 9.7±0.2 o-Xyl 10±0.1 9.7±0.3

Storage period

Analyte Day 0† Day 1 Day 2 Day 3 Day 5

A. 22°C —unpreserved (μg/g)

TDCE 5.1±0.1 5.2±0.3 4.8±0.2 5.0±0.2 4.8±0.1

Ben 11±0.3 11±0.6 9.4±0.5 0.84±0.70 ND*

TCE 11±0.2 12±0.6 11±0.4 11±0.2 11±0.1

Tol 9.2±0.2 9.4±0.3 8.4±0.3 6.9±0.3 ND

PCE 7.0±0.3 7.4±0.4 6.6±0.3 7.2±0.2 7.1±0.2

E-Ben 7.7±0.4 7.8±0.4 6.7±0.2 4.4±0.3 ND

p-Xyl 7.1±0.2 7.2±0.2 6.2±0.3 6.0±0.3 0.32±0.28

o-Xyl 7.9±0.4 8.0±0.3 7.1±0.3 7.8±0.1 6.3±0.2

Storage period

Analyte Day 0 Day 5 Day 13 Day 21 Day 28

B. 4°C—unpreserved (μg/g)

TDCE 5.1±0.1 4.8±0.1 4.8±0.2 4.8±0.2 4.8±0.2

Ben 11±0.3 11±0.1 4.2±0.2 ND ND

TCE 11±0.2 11±0.1 11±0.3 11±0.2 11±0.5

Tol 9.2±0.2 8.8±0.1 8.5±0.3 5.9±0.1 1.8±0.9

PCE 7.0±0.3 7.3±0.1 7.0±0.3 7.4±0.2 7.1±0.5

E-Ben 7.7±0.4 7.7±0.2 7.4±0.3 7.3±0.1 6.7±0.4

p-Xyl 7.1±0.2 7.3±0.1 7.0±0.4 6.1±0.1 1.8±0.8

o-Xyl 7.9±0.4 8.1±0.2 7.8±0.5 7.9±0.3 7.6±0.5

C. 22°C—preserved with NaHSO4 (μg/g)

TDCE 5.8±0.1 5.3±0.1 5.4±0.1 5.3±0.1 5.3±0.1

Ben 12±0.2 12±0.2 12±0.4 12±0.3 12±0.2

TCE 12±0.1 12±0.2 12±0.3 12±0.2 12±0.2

Tol 10±0.2 9.7±0.1 9.7±0.3 9.5±0.3 9.4±0.1

PCE 7.7±0.2 7.6±0.2 7.3±0.2 7.2±0.3 7.2±0.2

E-Ben 8.6±0.3 8.5±0.2 8.0±0.2 7.8±0.4 7.9±0.2

p-Xyl 8.0±0.1 7.7±0.1 7.6±0.2 7.2±0.3 7.2±0.1

o-Xyl 8.7±0.2 8.6±0.2 8.1±0.2 7.8±0.4 7.8±0.2

* ND = not detected, less than 0.02 μg of VOC/g † Same set used for day 0 values for unpreserved samples

tion of ortho-xylene (o-Xyl), all of the aerobically

degradable compounds were completely lost within five days (Fig. 7). The slower rate of degradation for o-Xyl is believed to be due to a steric

hindrance unique to orthoisomers.* In addition,

the aromatic compounds (benzene [Ben], toluene [Tol], ethyl benzene [E-Ben], para-xylene [pXyl] and o-Xyl) that could be easily identified in

the unpreserved soil samples treated with gasoline were also lost within this 5- to 9-day period,

when held at room temperature (Fig. 1). Furthermore, even the straight and branched chained aliphatics in gasoline that were not specifically identified, e.g., hexanes and pentanes, were degraded

rapidly at room temperature. Overall, these rates

of degradation for all of the analytes tested were

consistent with those extrapolated from aqueous

systems, where half-lives are on the order of days

for aromatic hydrocarbons and weeks to months

for the chlorinated compounds (Printup 1991).

* Personal communication with Thomas F. Jenkins,

CRREL, 1995.

8
Table 7. Set 4, trial 5. Mean and standard deviations of triplicate gasoline concentrations of spiking solution (μg) after 1

day of refrigerated storage, and for gasoline concentrations

(μg/g) in preserved and unpreserved samples stored at 22°

and 4°C.

Treatment aliquot

Analyte (μg)

gasoline 12±0.1

Storage period

Analyte Day 0† Day 5 Day 10 Day 14 Day 28

A. 22°C —unpreserved (μg/g)

Gasoline 11±0.7 6.7±0.5 0.6±0.1 0.09±0.01 ND

B. 4°C—unpreserved (μg/g)

Gasoline 11±0.7 11±0.4 8.9±0.5 9.5±1.7 7.8±0.9

C. 22°C—preserved with NaHSO4 (μg/g)

Gasoline 10±0.5 10±0.3 8.8±0.2 10±0.1 9.8±0.4

* ND = not detected, less than 0.02 μg of VOC/g † Same set used for day 0 values for unpreserved samples

Refrigeration (4°C) slowed the rate of degradation losses, but both Ben and meta-xylene (m-Xyl)

showed substantial reductions (>80%) within a

14-day storage period (Fig. 5, 8 and 12). With the

exception of o-Xyl, all of the other aromatic hydrocarbons were also substantially reduced (>95%)

in concentration over a 28-day period (Fig. 8, 12

and 13). These findings and others (Hewitt 1994,

Hewitt 1995a,b, Turriff 1995), suggest that refrigeration is not a sufficient means of eliminating

microbial degradation effects on VOC analyte concentrations in soil samples awaiting analysis.

In contrast, with the exception of styrene, all of

the aromatic analytes tested and the majority of

compounds present in gasoline were preserved

with NaHSO4 (Fig. 3, 6, 9, 14 and 15). The small

(<30%) concentration reductions that were observed relative to day 0 can be partly attributed to

slow sorption by the soil organic matter and lack

of an equilibration period between treatment and

the initial analysis. Additional evidence for this

mechanism is shown by the greater losses for compounds with the largest o/w partition coefficients

(n-propyl benzene [n-PB], iso-propyl benzene [isoPB], 1,3 dichlorobenzene [1,3 DCB], and n-BB), and

by the trend showing that the greatest reductions

in concentrations almost always occurred between

the first two analyses (day 0 to day 3 to 5, trials 1

through 3). Since a equilibrium condition most

likely has already been reached for environmental samples, VOC losses of this nature would not

be anticipated for samples taken during a site

investigation and preserved with NaHSO4.

Styrene was not stable in the soil preserved

with NaHSO4, perhaps because it either rapidly

polymerized or was chemically transformed into

an alcohol.* Since there was not enough water

present to create a slurry condition, NaHSO4 may

be either present as a salt or an acid. An additional experiment not reported here showed that the

loss of styrene was unique to soil samples preserved with NaHSO4; i.e., no losses were seen in

laboratory water that was similarly preserved and

stored. Thus, the chemical reaction that transforms

styrene most likely is catalyzed by the soil. Clearly, soil sample preservation by NaHSO4, or perhaps any acid, would not be compatible for investigations where styrene is a constituent of interest.

Although these experiments used only laboratory-fortified samples, field samples should behave similarly because chemical preservatives inhibited the activity of the indigenous soil microbes.

There are, however, some issues that need to be

addressed aside from the chemical transformation of styrene in soil due to preservation with

NaHSO4:

1. How should the samples be collected?

2. Are there any effects due to storage of samples in VOA vials?

3. Do all soil samples require chemical preservation?

4. Is it important to obtain a pH of 2 or lower

throughout the sample to inhibit microbiological

degradation?

While losses of greater than 80% for some analytes may be attributed to biodegradation when

soil samples held refrigerated for 14 days, much

* Personal communication with Thomas F. Jenkins,

CRREL, 1995.

9
Figure 6. Set 1/trial 1. Contaminated soil preserved

with NaHSO4 and stored at 22°C.

20

0 12345

Holding Time (days)

Ben

Tol

E-Ben

p-Xyl

o-Xyl

TDCE

TCE

PCE

Analyte Concentration (μg/g)

16

12

8

4

Figure 5. Set 1/trial 1. Contaminated soil stored at

4°C.

Figure 7. Set 1/trial 4. Contaminated soil stored

at 22°C.

greater losses occur when sample collection and

handling operations do not maintain the structural integrity or limit atmospheric exposure (Hewitt

et al. 1995). For instance, bulk samples that are

transferred to glass bottles using spatulas, spoons,

or paint scrapers, from which subsamples will be

removed for analysis after several days of storage, are often reduced in VOC concentration by

between 90 and 99.9% as compared to samples

collected using a single nondisruptive transfer

method (Hewitt 1994, Hewitt et al. 1995). Clearly,

how the sample is collected and handled has a

Figure 4. Set 1/trial 1. Contaminated soil stored at 22°C.

14

12

10

8

6

4

2

0 4 8 12 16 20

Holding Time (days)

Analyte Concentration (μg/g)

Ben

Tol

E-Ben

p-Xyl

o-Xyl

TDCE

TCE

PCE

12

8

4

0 4 8 12 16 20

Holding Time (days)

Analyte Concentration (μg/g)

Ben

Tol

E-Ben

p-Xyl

o-Xyl

TDCE

TCE

PCE

12

8

4

0 4 8 12 16 20

Holding Time (days)

Analyte Concentration (μg/g)

Ben

Tol

E-Ben

p-Xyl

o-Xyl

TDCE

TCE

PCE

10
0 20 30

Holding Time (days)

Ben

Tol

E-Ben

p-Xyl

o-Xyl

TDCE

TCE

PCE

10 20

Analyte Concentration (μg/g)

20

16

12

8

4

S

Figure 11. Set 3/trial 3. Contaminated soil stored

at 22°C.

0 10 20 30

Holding Time (days)

20

16

12

8

4

Analyte Concentration (μg/g)

Ben

Tol

E-Ben

p-Xyl

o-Xyl

TDCE

TCE

PCE

Figure 9. Set 1/trial 4. Contaminated soil preserved with NaHSO4 and stored at 22°C.

20

16

12

8

4

MC

1, 1 DCA

CF

1, 2 DCA

BDCM

1, 1, 2 TCA

CB

m-Xyl

0 4 8 12 16 20 24 28

Holding Time (days)

Analyte Concentration (μg/g)

Figure 8. Set 1/trial 4. Contaminated soil stored

at 4°C.

Figure 10. Set 2/trial 2. Contaminated soil

stored at 22°C.

0 4 8 12 16 20 24 28

CDCE

C-Tet

1, 2 DCP

Styrene

iso PB

n-PB

1, 3 DCB

n-BB*

(*× 10)

Holding Time (days)

20

16

12

8

4

Analyte Concentration (μg/g)

11
20

16

12

8

MC

1, 1 DCA

CF

1, 2 DCA

BDCM

1, 1, 2 TCA

CB

m-Xyl

0 4 8 12 16 20 24 28

Holding Time (days)

Analyte Concentration (μg/g)

4

Figure 12. Set 2/trial 2. Contaminated soil

stored at 4°C.

0 4 8 12 16 20 24 28

CDCE

C-Tet

1, 2 DCP

Styrene

iso PB

n-PB

1, 3 DCB

n-BB*

Holding Time (days)

20

16

12

8

4

Analyte Concentration (μg/g)

Figure 13. Set 3/trial 3. Contaminated soil stored

at 4°C.

20

16

12

8

4

MC

1, 1 DCA

CF

1, 2 DCA

BDCM

1, 1, 2 TCA

CB

m-Xyl

0 4 8 12 16 20 24 28

Holding Time (days)

Analyte Concentration (μg/g)

0 4 8 12 16 20 24 28

CDCE

C-Tet

1, 2 DCP

Styrene

iso PB

n-PB

1, 3 DCB

n-BB*

Holding Time (days)

Analyte Concentration (μg/g)

20

16

12

8

4

Figure 14. Set 2/trial 2. Contaminated soil

preserved with NaHSO4 and stored at 22°C.

Figure 15. Set 3/trial 3. Contaminated soil

preserved with NaHSO4 and stored at 22°C.

12
Table 8. Response (× 100) relative to fresh

standard of solutions preserved with

NaHSO4 and held refrigerated in either

an upright or inverted position.

Storage period

Analyte Day 7 Day 14 Day 21

Upright

TDCE 99.1±1.0* 102±4.9 96.2±3.6

Ben 101±0.1 104±5.3 96.5±0.0

TCE 97.7±0.7 100±4.6 94.1 ±5.2

Tol 99.7±1.1 103±4.8 95.2±1.7

PCE 94.3±0.6 93.9±4.6 86.9±6.1

E-Ben 99.4±12 103±7.12 93.4±3.2

p-Xyl 97.7±1.7 103±2.3 92.0±5.5

o-Xyl 100±0.4 106±1.7 95.3±2.4

Inverted

TDCE 99.7±1.1 100±0.8 97.7±2.7

Ben 101±1.4 104±2.1 98.6±2.0

TCE 99.3±0.7 100±2.1 94.4±2.4

Tol 101±1.0 102±2.2 97.9±0.9

PCE 95.9±0.7 94.2±1.4 87.7±3.6

E-Ben 102±0.8 102±3.1 94.8±3.1

p-Xyl 99.9±0.7 101±3.2 96.3±1.4

o-Xyl 102±1.6 104±5.8 98.7±2.7

Average and standard deviations n = 3.

Figure 16. Aqueous solution of set 1 analytes

preserved with NaHSO4 and stored at 4°C.

VOA Vial, Inverted

110

100

100

90

048

Holding Period (days)

% Relative to Standard

12 16 20

90

110

Ben

Tol

E-Ben

p-Xyl

o-Xyl

TDCE

TCE

PCE

VOA Vial, Upright

much bigger effect on the concentration of the

VOCs than biological degradation. However, if

measures are taken to limit exposure and maintain the structure of the soil during collection,

and if the soil sample is transferred to a vaportight bottle from which it can later be analyzed,

then additional precautions to prevent biological degradation should be taken.

All the samples in this study were stored in

sealed glass ampoules, vessels that do not lend

itself to field sampling practices, and to which

samples could not be transferred without significant volatilization losses. One of the more common vessels for soil sample collection, storage and

shipping is VOA vials. These vials have a Teflonfaced silicone septum for the purpose of sealing

and inhibiting VOC losses; however, this polymeric material has been shown to sorb VOCs from

solution (Gilham and O’Hannesin 1990; Parker

and Ranney 1994; Parker and Ranney, in press).

To see if VOCs associated with soils stored in a

VOA vial would also tend to be lost to Teflon, the

following experiment was performed. Eighteen

aqueous samples of the set 1 analytes were prepared by spiking 30 mL of laboratory water preserved with 0.25 g of NaHSO4 and stored refrigerated (4°C) in 40-mL VOA vials (Eagle Picher).

Half of these replicate solutions were stored upright and half were stored inverted. Triplicate samples of each type were removed and analyzed

after 7, 14 and 21 days of storage, and analyte

concentrations were determined based on a fresh

standard prepared from the same stock solution

used to prepare the samples. In this case all analyses were performed on a field-portable PhotoVac 10S10 gas chromatograph (Hewitt et al. 1992).

The results of this experiment showed that PCE

in either the gaseous or liquid phase tended to be

lost from the vials (Table 8, Fig. 16). Similar results were established for unpreserved aliquots of

the spiking solution transferred to 20-mL auto

sampler VOA vials with Teflon-lined caps

(Wheaton, Table 6). Perchloroethylene had been

identified as one of the analytes showing the greatest rate of loss in earlier solution studies (Parker

and Ranney 1994, Parker and Ranney in press).

Based on these findings we can assume that some

small losses (5 to 15%) will be incurred when either a soil or liquid sample contaminated with

VOCs is stored for an extended period (28 days)

in a VOA vial with a Teflon-lined cap. However,

the probable loss mechanism results from the ability of VOCs to pass through this material and not

because of sorption (Barbeau et al. 1995). Sorption

13
onto glass is another possible explanation, but

appears unlikely in light of the stability of this

analyte in glass ampoules for the experiment with

an equilibration period (Table 6).

Furthermore, these losses are analyte specific

and are likely to be condition dependent (i.e., storage temperature); thus more detailed studies are

warranted. Until such information is available,

we recommend that even chemically preserved

samples be stored refrigerated.

The soil in this study was obtained within 10

cm of the ground surface. In this horizon there is

typically more organic carbon and consequently

more biological activity, as compared to soils obtained from greater depths in the vadose zone.

However, substantial evidence exists showing that

even subsurface soils with organic carbon of less

than 0.5% become biologically active once oxygenated. Hence in-situ aeration systems are being

developed to enhance bioremediation of subsurface oil and gasoline spills (Downey et al. 1994,

Germann and Friesen 1994). Since all conventional sampling methods expose soil samples to the

atmosphere during collection and handling operations, previously oxygen limited biodegradation

reactions could be initiated. For this reason chemical preservation is likely to be necessary whenever aromatic hydrocarbons are of concern.

With regard to whether a slurry condition is

needed to evenly distribute the preservative, an

earlier experiment where 1 mL of water was added to preserved soil ampoules before spiking to

slurry the soil matrix (Hewitt 1995b) was not significantly different (95% confidence level) from

those without excess water. However, laboratorytreated soil does not mimic the cohesiveness of a

native soil. Until more information is available, a

conservative approach should be recommended.

Therefore, enough water should be present in the

VOA vial to create a slurry condition, once the

soil sample has been introduced. Furthermore,

preservation methods that would not rely on acidification (i.e., mercuric chloride) would be necessary when carbonates were present.

CONCLUSION

By preserving with NaHSO4, treated soil samples held at 22°C showed stable VOC concentrations for up to 28 days. This chemical preservation method would complement collection

protocols that minimize volatilization losses during collection, storage and analysis for soil with

low carbonate levels. Confinement of samples in

vaportight vessels throughout handling and analysis procedures is critical to the accurate assessment of both biological degradation and chemical

preservation of VOCs in soil. Using such protocols allows investigators to determine if measures

other than refrigeration are necessary or effective

in maintaining stable VOC concentrations over

regulated holding times.

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Eds.). Madison, Wisconsin: Soil Science Society of

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Downey, C.D., P.R. Guest and J.W. Ratz (1994)

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Environmental Technology Symposium, Williamsburg,

Virginia, June, p. 223–234.

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Collection, handling, and storage: Keys to improved data quality for volatile organic compounds in soil. American Environmental Laboratory,

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Waste, Vol. 1B. U.S. Environmental Protection

Agency, SW–846.

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November 1995

Enhanced Preservation of Volatile Organic Compounds in Soil

With Sodium Bisulfate

Alan D. Hewitt

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 95-26

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland 21010-5401 SFIM-AEC-ET-CR-95081

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

23

Biodegradation Sodium bisulfate

Preservation Volatile organic compounds

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

Sodium bisulfate (NaHSO4) was evaluated as a means of chemically preserving soil samples to prevent the

microbiological degradation of volatile organic compounds (VOCs). Laboratory sample treatment consisted of

spiking soil samples held in glass ampoules with aqueous solutions containing eight different VOCs or gasoline

and then sealing them to eliminate volatilization as a concern. Samples preserved with NaHSO4 were held at

room temperature (22°C), while equal numbers of unpreserved samples were stored refrigerated (4°C) and at

room temperature. Results show that concentrations of all of the halogenated hydrocarbons tested (14) remain

fairly constant, independent of temperature or preservation. In contrast, all the aromatic hydrocarbons (10)

tested as separate analytes, or ones that could easily be identified in gasoline, experienced a complete (>95%)

loss when held for nine days at room temperature. Refrigeration reduced the rate of biodegradation, but two

aromatic hydrocarbons showed substantial losses (>80%) within the currently recommended 14-day holding

period. Over a 28-day refrigerated period, reductions of greater than 95% occurred for 9 of 10 aromatic

hydrocarbons tested. With the exception of styrene, chemical preservation by introducing NaHSO4 mitigated

the loss of all of aromatic hydrocarbons tested over a 28-day holding period when samples were stored at room

temperature. Therefore, NaHSO4 preservation is one way of effectively eliminating biodegradation of VOCs in

soil samples intended for low level (<1-μg/g) analysis.