Polynuclear aromatic hydrocarbon (PAH) release from soil during treatment with Fenton's reagent

0045-6535(95)00274-X

POLYNUCLEAR

AROMATIC

HYDROCARBON

DURING TREATMENT

Chemosphere. Vol. 31, No. 9, pp. 4131-4142. 1995 Elsevier Science Ltd Printed in Great Britain

(PAH) RELEASE FROM SOIL

WITH FENTON’S REAGENT

Fred K. Kawahara*, Brunilda Davila, Souhail R. Al-Abed**, Stephen J. Vesper**, John C. Ireland, Steve Rock

US Environmental Protection Agency, Cincinnati, Ohio 45268 ** Department of Civil and Environmental Engineering. P.O. Box 210071, University of Cincinnati, Cincinnati, Ohio 45221-0071

(Received in USA 20 June 1995; accepted 5 September 1995)

ABSTRACT

Fenton’s Reagent was used to treat soil from a wood-treating site in southeastern Ohio which had been contaminated with creosote. Slurries, consisting of 10 g of contaminated soil and 30 mL water were treated with 40 mL of Fenton’s Reagent (1: 1 of 30% Hz02 : 8.84 mh4 FeSOd). Concentrations of fourteen PAHs were monitored during 24 hours treatment. In preliminary experiments, we observed a significant increase in the extractibility of the PAHs after 1 hour of treatment. Twelve of the fourteen PAHs showed consistent increases (13 to 56%) in extractibility from soil after one hour of contact time with the Reagent, Only acenaphthylene and acenaphthene showed no increase in extractibility. Electron exchange by structural iron in clay mineral and the swelling of clay layers is proposed as the release mechanism of tightly held PAHs. Results obtained in this study suggest that this treatment may enhance soil remediation. The results also indicate that the PAH analytical method employed may provide inaccurate results in some situations.

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INTRODUCTION

Polynuclear aromatic hydrocarbons

(PAHs) are a group of chemicals with two or more fused

benzene rings (Cemiglia, 1992). They are primarily produced as a result of the combustion of fossil tieIs especially from coal gasification, waste incineration, and in the manufacture of fossil fuel derived products, e.g. creosote (Lijinsky 1991). The United States Environmental

Protection

Agency lists PAHs as priority pollutants (Mueller et al., 1989), since some are carcinogens or mutagens (Thacker et al., 1985; Dipple et al., 1990).

The wood-preserving

industry is one of the major users of creosote.

composed of approximately

Coal tar creosote is

85% PAHs (Mueller et al., 1989). About 700 active or inactive

wood treating sites are located in the United States alone (Mueller et al., 1989). The creosote preservation

process can result in spills, leakage from tanks, escape from holding ponds or from

dripping racks that are not properly maintained.

The extent of spilled PAHs adsorption onto soil

surfaces by van der Waal’s forces is governed by the PAHs chemical structure and soil chemicaVmineralogica1 properties (Chiou et al, 1986).

The US EPA regulates the removal, treatment, wastes containing PAHs. The technology available technology.

and ultimate disposal of contaminated

soils and

selected for treating such soils is based on the best

One method of treating PAH contaminated

soil is with incineration.

To

avoid hazardous combustion products, chemical and biological treatments have been considered by the US EPA as alternative treatment technologies

to incineration.

Hydrogen peroxide has the ability to vigorously oxidize organic compounds,

even those with an

aromatic moiety. The ultimate products are carbon dioxide and water. The basic oxidation reaction is as follows:

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Hz02 + C,H, = xHZO + nC0z

Hydrogen peroxide is more effective as an oxidant when used in the presence of ferrous ion (Fenton’s Reagent). The interaction of Fe2’ ions with hydrogen peroxide involves the generation of many intermediates including hydroxyl radicals. Iron sulfate catalyzes the decomposition of hydrogen peroxide, producing hydroxyl radicals according to the following ferrous ion reaction (Walling, 1975):

Fe2’ + H202 a Fe3’ + OK + OH.

The generation of hydroxyl radicals (OH.) in sufficient quantity enhances oxidation and thus degradation of organic compounds (e.g. PAHs). Hydroxyl radicals, very reactive and nonspecific radicals, attack organic molecules by abstracting hydrogen atoms or by adding to double bonds (Sundstrom et. al., 1989).

Structural iron in clay minerals can be reduced or oxidized due to peroxide oxidation. In addition, electron exchange by structural iron causes the swelling of clay layers due to association of water molecules with newly hydroxylated ferric ion in the clay matrix. This swelling increases the space between clay layers and thus releases contaminant molecules trapped between the layers. Middleton etal. (1991) have shown that certain portions of PAHs in soil were physically occluded. These portions were shown be dependent on soil mineral composition. The objective of this study was to examine the effect of the treatment of PAHs in soil with Fenton’s Reagent and explain our observations about the apparent increase in extractable PAH concentration after one hour exposure to Fenton’s Reagent.

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EXPERIMENTAL

PROCEDURES

AND ANALYSIS

Soil from the wood treating site in southeastern Ohio was shipped in refrigerated coolers and tested in the Summer of 1993. For all experiments (unless otherwise stated), ten grams of soil and 30 mL of deionized water were added to 125 mL Erlenmeyer flasks. For the Fenton’s Reagent, fresh 30% hydrogen peroxide (Fisher, Chicago, IL) and 8.84 mM ferrous sulfate (Fisher, Chicago, IL) were used. The slurries were mixed on a gyrotary water-bath (New Brunswick Inc, New Brunswick, NJ) at 175 rpm and incubated at 25°C. in the dark. All samples were analyzed by extracting first with methylene chloiide in a Tecactor Soxtec extractor (Fisher, Chicago, IL) using EPA Draft Method 3561 and analyzed by GUMS using EPA Method 8270B (USEPA, 1994). All samples were gravity filtered to remove the water and allowed to air dry. Since all PAHs, with the exception of a few hydrogenated derivatives, are solids at ambient temperatures and are the least volatile of the hydrocarbons (Lee et al, 198 I), we assumed that the volatilization of PAHs during the experiment was minimal.

Soil Characterization:

Size classification was performed using standard soil sieves (ASTM

Method D421-58). Elements composition was determined by ICP-MS (EPA Method 200.8). Soil pH was measured after adding 5 mL of deionized water to 5 g of soil and mixing for 30 min. The soil was allowed to settle for 1 hr, then the pH was measured using a soil pH probe (Orion, Boston, MA).

Fenton’s Reagent Concentration

and Method of Addition: Fenton’s Reagent was added to

the soil slurry by dripping. A peristaltic pump (Cole Parmer, Niles, IL) with two identical heads (one for the peroxide and the other for the ferrous sulfate) was used to make the additions of 20 mL of each component. Three flasks were prepared, as described above, for times 0, 1,4, and 24 hr. The Fenton’s Reagent was applied quickly (about 30 min.) by adding the Fenton’s Reagent components. The reaction flasks were removed at the designated time and immediately analyzed (as described above). Each sample was dewatered and extracted before analysis. Triplicate

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values were obtained for each sample analysis. A total of 168 samples were analyzed for the fourteen PAHs. Each of the four time period samples were analyzed in three replications.

RESULTS AND DISCUSSION

As expected, the Fenton’s Reagent was effective in reducing the concentrations of PAHs in this soil (Figures 1 to 4). Results show that the amount of PAHs remaining after 24 hr of oxidation with Fenton’s Reagent was in the range of 7% (Acenaphthylene) to 28% (Naphthalene), after being corrected for the weight addition to the original amount in the soil. The values of naphthalene and 2-methylnaphthalene have the highest percentages of original mass left unreacted by the OH. free radicals. This may be due to their initial high concentration in the soil, intercalation between clay layers more tightly (less accessible to extraction), or their resistance to oxidation.

Unexpectedly the concentrations of twelve of the fourteen PAHs studies appeared to increase in a range from 13 to 56% relative to the initial analysis, after one hour of exposure to Fenton’s Reagent. We also noted that the soil in the reaction flasks nearly doubled in volume and appeared very dispersed. In the following discussion, we propose an explanation for these observations.

The Soil sample used in these experiments was analyzed for the concentration of 11 metals (Table 1).

TABLE 1: Concentrations of 11 elements in PAH contaminated soil determined by ICP/MS (EPA Method 200.8). Element

Al

Mn

Na

K

Mg

Fe

Cu

Zn

Pb

Ni

Ba

Concentration

8220

500

182

1210

2170

17,300

19

121

17

109

85

Wg)

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Soil conditions and chemistry are critical to the use of Fenton’s Reagent (Smith and Norman, 1963). The pH of this soil was 7. The concentration of metals was typical of soils from southeastern Ohio. Since the pH was above 6, it is likely that the iron would be in the Fe3’ oxidation state. Particle size analysis indicates that the soil has 17.6% clay (Table 2). Clay particles are more reactive than any other size fraction in soil due to high surface charge, surface area, pH sensitivity, and adsorption capacity (Middleton et al, 1991). Therefore, some of the PAHs were probably tightly held in the clay fraction.

TABLE 2: Particle Size Analysis of PAH Contaminated Soil determined by ASTM Method D421-58.

Particle Separate

%IWeight

Gravel

23.8

Sand

21.9

Silt

36.7 17.6

The Fenton’s Reagent makes the PAHs more available to extraction in the first hour of exposure (Figures 1 to 4). The large increase is probably due to the iron ions complexing with the PAHs and weakening the adsorptive bonds of the PAH-complex formed with soil surfaces. The ironaromatic complex is extractable with methylene chloride. The PAHs occluded from solvent in the soil particles may have become more available due to the weakening of the adsorptive bonds of the aromatic with the soil surfaces. PAHs occluded in the internal surfaces between internal clay mineral sheets may become more available to extraction by the solvent as interstitial spaces begin to swell on exposure to Fenton’s Reagents. The exceptions, acenaphthylene and acenaphthene (Figure 1 and 3) appeared to be readily accessible to the solvent, methylene chloride, from the beginning. This is probably due to the fact that the structures of both of these molecules are bent

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and not as planar on the surface of the soil as the other twelve PAHs and thus they may not be significantly trapped between clay layers. For the remaining twelve PAHs, we believe that the addition of the Fenton’s Reagent increased the amount of extractable PAHs ostensibly as a result of contact with ferrous-ferric

ions.

The ability of clays to shuttle electrons between structural redox centers (Fe2’.3’) and organic molecules adsorbed on the external or internal surfaces allows the PAHs to be released.

The iron

on the internal surfaces is able to engage in redox reactions with contaminant molecules encapsulated

within the clay layers by changing them into charged radicals; thus, making them

more easily extracted.

These redox processes can be illustrated by the following equation:

[Fe”] + Ar 9

[Fe’*“] + Arm’

This electron transfer reaction was demonstrated

by Rzenson and Heller-Kallai (1978). During

this reaction, Fe2+.3+in the clay lattice can accept or donate electrons.

For the electron to be

transferred from the aromatic ring to the iron ion center, the iron ions must be partially dehydrated to allow for the close approach of the two species and for the binding of the aromatic ring to the metal center via electron donation (Warren et al, 1986). Furthermore, Fe*’ to Fe3’ in the octahedral layer of the clay transformed into a high-swelling

smectite (Egashira and Ohtsubo,

the oxidation of

a low-swelling smectite (clay mineral)

1983). Oxidized structural iron attracts

hydroxyl radicals into the internal surfaces of the clay and thus causes clay to expand and increase in volume (swelling).

This expansion may have allowed the solvent to reach tightly held PAHs

between clay layers due to the association of water molecules with the hydroxylated ferric ion in the clay structure.

The point should be made that the extrapolation

of the concentration

curves to zero time would

result in even greater differences between measured zero time concentrations be true zero time concentration.

and what appears to

This suggests that the standard procedure used to analyze soil

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FIGURE

I: The Concentration

of extractable (acenaphthylene.

naphthalene. 2-methylnaphthalene,

and

benzo(a)pyrene) from the Fenton’s Reagent treated soil at 0. I, 4, and 24 boors. All samples were analyzed by extracting the soil with methylene chloride in a tecactor soxtec extractor using EPA draft method 3561 and analyzed by GCiMS using EPA method 8270B.

1 1401

n

-I

120

100:

g

-C<-

acanaphthyiene naphtialene

+

Z-methylnaphthalene

-a-

benm(a)pynne

1; d

i

c

40-

?z

2

20 O-

0

5

10

1s

20

25

30

nmmm FIGURE 2: The Concentration

of extractable (dibenzofuran,

from the Fenton’s Reagent treated soil at 0.1.4,

chrysene, beruo(b)fluoranthene,

benzo(a)anthracene)

and 24 hours. All samples were analyzed by extra&g

the soil

with methylene chloride in a tecactot soxtec extractor using EPA draft method 3561 and analyzed by Gc/Ms EPA method 8270B.

600

-

I-

Cl-

-I 0

s

10

20

IS

nma (hrs) 8

25

30

using

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FIGURE 3: The Concentration of extractable (pyrene, fluorene. accnaphthene) from the Fenton’s Reagent treated soil at 0, 1,4, and 24 hours. All samples were analyzed by extracting the soil with methylene chloride in a t-or soxtec rxtractor using EPA draft method 3561 and analyzed by G0M.S using EPA method 82708.

1600

’

1

1400

-z s s6

12w

-

la00

-

= g

600 -

B

600 -

0 = 2

-z-

pyrene

-z-

i%Xl-Sfle

*

aconachhenc

4w-

200 OS

0

10 1s nrne (hn)

20

2s

30

FIGURE 4: The Concentration of e,xtmctable(fluoranthene. phe.nanthrene, anthracene) from the Fenton’s Reagent treated soil at 0, 1.4. and 24 hours. All samples were analyzed by extmcting the soil with mcthylene chloride in a tecactor sox& extraaor using EPA draft method 356 I and analyzed by GC%fS using EPA method 8270B.

--o 2soo g 2000 -

-Z-&--

R

lluomnthena phemnthmne analncEna

3 i 1saa 1 10000 3

saaQ-

0

s

10

15

nma (hrs) 9

20

25

30

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for PAHs may not truly reflect the actual concentrations of PAHs in soil.

CONCLUSION

The Fenton’s Reagent was effective in enhancing the extraction of the PAHs from this particular soil. We believe that the presence of iron and changing the soil oxidation state enhances the release of some PAT-Bfrom tightly held positions between clay layers in the first hour. Further studies are necessary to demonstrate the actual mechanism of this process, Enhanced extraction efficiency of PAHs due to Fenton’s Reagent might necessitate a modified analytical procedure.

Acknowledgments - Although the research described in this article was funded wholly or in part by the United States Environmental Protection Agency under the assistance agreement 6%C9003 1 to the University of Cincinnati, it has not been subjected to the Agency’s Review and therefore does not necessarily reflect the views of the agency, and no official endorsement should be inferred. The information presented in this article does not constitute endorsement, recommendation, or use of commercial products by the USEPA. We would like to thank D. Fred Bishop, Carl Brunner, Teresa Hat-ten, and Michael Roulier for their helpful discussion of this paper. We would also like to thank Sam Hayes and Melissa Bowlin for their analytical help in the PAH measurements.

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REFERENCES

Chiou, C. T., Malcolm, R. L., Brinton, T. I., and Kile, D. E. 1986. Water solubility enhancement of some organic pollutants and pesticides by dissolved humic and tilvic acids.

Environmental Science and Technology 20:502-508.

Dipple, A. Cheng, S. C., and Bigger, C. A. H. 1990. Polycylic aromatic hydrocarbon carcinogens,

pp. 109-127. In: Mutagens and Carcinagens in the Diet. pp. 109-127.

(Paiza, M. W., Aeschbacher,

H. U. Felton, J. S. and Sato, S., Eds.), Wiley-Liss.

Egashira, K. and Ohtsubo, M. 1983. Swelling and mineralogy of smectites in puddy soil derived from marine alluvium, Japan. Geodmna 29: I 19- 127.

Gauger, W. K. Kelley, R. L., and Srivastava, V. J. 1992. Application of pretreatment

step in biological degradation

Gas, Oil Coal, and Environmental

of polyaromatic

Biotechnology

Fenton’s Reagent as a

hydrocarbons,

pp. 105-120.

II. Institute of Gas Technology,

Chicago.

Kremer, M. L. 1963. Oxidation-reduction

step in catalytic decomposition

of hydrogen peroxide

by ferric ions. Trans. Faraday Sot. 59:2535-42.

Lijinsky, W. 199 1. The formation and occurrence

of polynuclear aromatic hydrocarbons

associated with food. Mutat. Rex 259:25 l-26 I.

Middleton A.C., D.V. Nakles, D.G. Linz. 1991. The influence of soil composition biremediation

of PAH-contaminated

Soils. Remediation Autumn:391-406

on

4142

Mueller, J. G. Chapman, P. J., and Pritchard, P.H. 1989, Creosote-contaminated sites. Environ. Sci. Technol. 23: 1197-1201.

Smith, J. R. and Norman, R. 0. 1963. Hydroxylation Part I: The oxidation of benzene and toluene by Fenton’s Reagent. J. Chem. Sot. 13: 2897-2906.

Rozenson, I., and L. Heller-Kallai. 1978. Reduction and oxidation ofFe’+ in dioctahedral smectites-III. Oxidation of octahedral iron in montmorillonite. CZaysand CfuyA4inerulogv 261%92.

Solomon, D. H.,and D. G. Hawthorne. 1983. Chemistry of pigments and tillers. John Wiley and Sons, New York.

Sundstorm, D., Weir, B., Klei, H. 1989. Destruction of aromatic pollutants by UV light catalyzed oxidation with hydrogen peroxide. Environmental Progress 8:6- 11.

U. S. EPA, 1990. Test methods for evaluating solid waste, physical/chemical methods. SW-846, U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, 3rd ed., Washington, D.C. Method 8270B, Table 2, Revision 2, Sept. 1994.

Walling, C. 1975. Fenton’s Reagent revisited. Act. Chem. Res. 8: 125-131.

Warren, D.S., A.I. Clark, and R. Perry. 1986. A review of clay-aromatic interactions with a view to their use in hazardous waste disposal. Science of Total Environment 54: 17-172.