PB-244 139
BENZENE. ENVIRONMENTAL SOURCES OF CONTAMINATION,
AMBIENT LEVELS, AND FATE
P. H. Howard, et al
Syracuse University Research Corporation
Prepared for:
Environmental Protection Agency
December 1974
DISTRIBUTED BY:
KUTl
National Technical Information Service
U. S. DEPARTMENT OF COMMERCE
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Reproduced by
NATIONAL TECHNICAL
INFORMATION SERVICE
US Department of Commerce
Springfield, VA. 22151
OF TOXIC SUBSTANCES
Ul PROTECTION AGEHCY
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TECHNICAL REPORT DATA '
(PteaumdlMtaitlleiu on the tevmebefort completing
1. REPORT NO.
EPA 560/5 - 75-005
2.
4. TITLE AND SUBTITLE
Sources of Contamination, Ambient Levels, and
Fate of Benzene in the Environment
PB 244 139
B, REPORT DATE
Decembr 1974
B. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
P.H. Howard and P.R.'Durkin
B. PERFORMING ORGANIZATION REPORT NO.
V
TR 74-591 v
0. PERFORMING ORGANIZATION NAME AND ADDRESS
Life Sciences Division
Suracuse University Research Corporation
Merrill Lane, University Heights
Syracuse, New York 13210
10. PROGRAM ELEMEN NO.
2LA328
.
NO.
68-01-2679
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Toxic Substances
Environmental Protection Agency
Washington, DC 20460
13, TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
18. SUPPLEMENTARY NOTES
16. ABSTRACT
This report reviews and evaluates available information pertinent tx> an assessment
of benzene contamination of the environment. Benzene losses from commercial
(production and use) and non-commercial (automotive emissions and oil ispills) sources
were considered. It is estimated tha^.of the total quantity that is released to
the enviornment taore than half results from motor vehicle emissions. Monitoring
data somewhat support this contention. Available information on the ^environmental
persistence of benzene suggests that it degrades slowly.
»'
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
benzene, environmental
fate, 'environmental
persistence, monitoring,
environmental transport
6A, 6C, 6F, 6J,
6T, 7A, 7C
18. DISTRIBUTION STATEMENT
Document is available to the public
through the National Technical Information
Service, Springfield, Virginia, 22151.
19. SECURITY CLASS (TMtKtfortT
31. NO. OF PAGES
I
nclassified
. SECURITY CLASS (TMl
Unclassified
I.
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EPA 560/5-75-005 TR 74-591.1
Sources of Contamination,
Ambient Levels, and Fate of Benzene
in the Environment
By
P.H. Howard
P.R. Durkin
Life Sciences Division
Syracuse University Research Corporation
Merrill Lane, University Heights
Syracuse, New York 13210
December 1974
Contract No. 68-01-2679
Project L1240-05
Project Officer
Carter Schuth
Prepared for
Office of Toxic Substances
U.S. Environmental Protection Agency
Washington, D.C. 20460
id/
-------
NOTICE
The report has been reviewed by the Office of Toxic Substances,
EPA, and approved for publication. Approval does not signify
that the contents necessarily reflect the views and policies
of the Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or
recommendation for use.
ii
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ABSTRACT
This report reviews and evaluates available
information pertinent to an assessment of benzene
contamination of the environment. Benzene losses
from commercial (production and use) and non-commercial
(automotive emissions and oil spills) sources are
considered. It is estimated that of the total
quantity that is released to the environment more than
half results from motor vehicle emissions. Monitoring
; . ' i.t,,
data somewhat support this contention. Available
information on the environmental persistence of benzejoe
suggests that it degrades slowly.
ill.
-------
. TABLE OF CONTENTS
ABSTRACT ' til
I. INTRODUCTION 1
II. CHEMICAL STRUCTURE AND PROPERTIES 1
III. BENZENE CHEMISTRY . 4
A. Reactions Involved in Uses 4
B. Hydrolysis 4
C. Oxidation 6
D. Photochemistry 1
IV. ENVIRONMENTAL EXPOSURE FACTORS AND MONITORING 10
A. Benzene Contamination from Commercial Sources 10
1. Production 10
2. Losses from Commercial Uses 16
B. Benzene Contamination from Non-Commercial Sources 18
C. Environmental Monitoring and Analysis 23
1. Analysis Techniques 23
2. Monitoring Data 27
V. ENVIRONMENTAL FATE
A. Degradation or Alteration Processes 30
1. Biological Transformation of Benzene 30
2. Chemical and Photochemical 5'0
B. Transport 50
VI. EVALUATION 52
A. Summary 52
B. Recommendations '54
REFERENCES '57
iv
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TABLE OF FIGURES
Title Page
1. Electronic Absorption Spectra of Benzene, Naphthalene
Phenanthrene, Anthracene, and Naphthacene 8
2. Ultraviolet Absorption Spectra 8
3. Commercial Uses of Benzene and Benzene Derivatives 11
4. Geographical Location of Benzene Production Plants 15
5. Geographical Location of Benzene By-Product
Manufacturing Plants 21
6. Microbial Degradation of Benzene to Catechol 36
7. Ortho Fission of Catechol by Pseudomonas putida and
Moraxella Iwoffii and Meta Fission of Catechol by a
Pseudomonas sp. 37
8. Benzene Ortho Fission Pathways by Pseudomonas putida
and Moraxella Iwoffii and Meta Fission by a
9.
10.
Pseudomonas sp.
Proposed Pathways of Mammalian Benzene Metabolism Based
on Studies with Rats and Rabbits
Primary Metabolic Pathways of .'Benzene in Rabbits as
Proposed by Carton and Williams
38
39
40
11. The In Vitro Metabolism of Benzene Oxide Using Rabbit
Liver Microsomes and Soluble Fraction 44
12. Elimination of Benzene in Exhaled Breath of One Subject
After Unspecified Experimental and Occupational
Exposure of About 4 Hours 47
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TABLE OF TABLES
Title
I. Properties of Benzene 2
II. Physical Specifications of Commercial Benzene 3
III. Commercially Important Reactions of Benzene 5
I O
IV. Benzene Consumption
V. Petroleum Based Benzene Production Plant Location... 13
VI. Coke-Oven Operators Producing Coal-Derived Benzene 14
VII. Upper Limit of the Amount of Benzene Lost from
By-Product Manufacturing Facilities 17
VIII. By-Product Manufacturing Plants 19
IX. Comparisons of Benzene Emissions for 1971 23
X. Preconcentration Techniques for Analysis of Benzene
in Air and Water Samples 26
XI. Ambient Monitoring Data for Benzene 28
XII. Degradation of Benzene by Mixed Cultures of
Microorganisms 31
XIII. Pure Cultures of Microorganisms which Degrade Benzene ;35
14
XIV. Metabolic Fate of a Single Dose of C-labelled Benzene
Administered to Rabbits by Gastric Intubation .,46
XV. The Eactors and Times of Post-Exposure Observations,
Benzene Doses and Excretions .48
vi
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I. INTRODUCTION
This report reviews and evaluates available information that is
pertinent to an assessment of benzene contamination of the environment.
i
Physical and chemical properties, monitoring data, and environmental fate
information are considered. In addition, the possible sources (both natural
and man-made) of benzene in the environment are reviewed and quantitatively
compared.
II. CHEMICAL STRUCTURE AND PROPERTIES
"Benzene, C,H,, is a volatile, colorless, and flammable liquid aromatic
hydrocarbon, which possesses a very characteristic odor" (Ayers and Muder,
1964). The compound consists of a planar molecule with six carbon atoms
formed into a hexagon. Several chemical structure representations of benzene
have been suggested (e.g. the Kekule structures I and II), but the most frequently
H
H
Kekule Ring Abbreviated
Formula Kekule Formula ,
I II III
used formula, which gives a more realistic picture of the structure of benzene,
is depicted by a hexagon with a circle in the middle (III). Each C-C and C-H
bond in benzene is 1.39A and 1.08A long, respectively.
Benzene possesses greater thermal stability than would normally be pre-
dicted from the Kekule formula (3 double and 3 single C-C bonds). This difference
(36.0 kcal/mole) between the energy required for dehydrogenation of cyclohexane
-------
to benzene and the energy normally required for the formation of three double
i
bonds is attributed to the resonance energy of benzene. The resonance energy
is considered to be due to the interaction of the six IT electrons which form
"doughnut" shaped electron orbitals above and below the plane of the ring.
A number of physical properties of benzene are listed in Table 1.
The water solubility (1800 ppm) and volatility (vapor pressure - .
100 mm Hg at 26°C) are important parameters to environmental considerations.
These parameters are temperature dependent and may be affected by various
environmental conditions. For example, McAuliffe (1963) has reviewed a number
Table I. Properties of Benzene (Ayers & Muder, 1964)
Constant Value
fp, °C 5.553.
bp, °C 80.100
density, at 25°C,g/ml 0.8737
vapor pressure at 2(S.0759C,mm Hg 100
refractive index, M*5 1.49792
viscosity (absolute) at 20°C, cP 0.6468
surface tension at 25°C, dyn/cm 28.18
critical temp, °C 289.45
critical pressure, atm 48.6
critical density, g/ml 0.300
flash point (closed cup), °C -11.1
ignition temp in air, °C 538
flammability limits in air, vol % 1.5-8.0
heat of fusion, kcal/mole 2.351
heat of vaporization at 80.100°C, kcal/mole 8.090
heat of combustion at constant pressure and
25°C (liquid CeH6 to liquid H20 and
gaseous C02), kcal/g 9.999
solubility in water at 25°C, g/100 g water 0.180
solubility of water in benzene at 25°C, g/100
g benzene, 0.05
-------
of reported values (1730-1790 ppm) for the solubility of benzene in water.
The variation is probably attributable to different temperatures or the low
precision of the techniques. Both salting-in and salting-out (increase and
decrease in solubility) effects have been noted for benzene in aqueous solu-
tions (Giacomelli and Spinetti, 1972). Button and Calder (1974) have noted
a decrease in the solubility of higher molecular weight n-paraffins in salt
water compared to distilled water. A similar decrease occurs with the
water soluble fraction (including benzene) of crude oils (Lee et al., 1974).
Thus the solubility of benzene in salt water is probably less than the
reported distilled water value.
The benzene product available commercially is extremely pure. The
specifications for the various commercial products are noted in Table II.
Table II. Physical Specifications of Commercial Benzene
(ASTM D835, 1973; ASTM D2359, 1974)
Industrial Grade
Distillation Range,
760 mm Not more than
2°C including 80.1°C
Specific Gravity,
15.56/15/56°
Thiophene
Itonaromatics
0.875-0.886
Refined
Not more than
1°C including 80.1°C
0.8820-0.8860
1 ppm max
0.15 percent max
Refined
(Nitration Grade)
Not more than
1°C including 80.1°C
0.8820-0.8860
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Gas chromatographic analysis has shown that no more than about 0.2% and usually
no more than 0.1% hydrocarbon impurities (e.g. paraffinic, cycloparaffinic,
olefinic hydrocarbons and toluene) are found in commercial benzene which has a
boiling range no greater than 1°C. Other impurities in the commercial product
include traces of thiophene and carbon disulfide (Ayers and Muder, 1964).
III. BENZENE CHEMISTRY
This section reviews chemical reactions which are commercially or
environmentally important. Since the major commercial use of benzene is as a
chemical intermediate, the number of commercial reactions is quite large.
A. Reactions Involved in Uses.
Benzene is an important building block for a number of high volume
chemicals including ethylbenzene (raw material for styrene), phenol, dodecyl-
benzene (raw material for surfactants), nitrobenzene (raw material lor aniline),
cyclohexane, chlprobenzene (raw material for DDT), dichlorobenzenes, and maleic. ..
anhydride. Table III depicts the commercial chemical reactions and the yields
and conditions used to make the derivatives of benzene. In all cases, these
reactions are carried out with catalysts, strong acids, or elevated temperatures
and/or pressures and, therefore, are not likely environmental processes.
B. Hydrolysis
The benzene ring does not react with water or hydroxyl ions (OH )
unless it is substituted with a sufficient number of powerful electronegative
groups. For example, nitrobenzene reacts with strong sodium hydroxide to give
o-nitrophenol (Ayers and Muder, 1964). Thus hydrolysis of benzene, .which con-
tains no electronegative substituents, is an extremely slow process^which occurs
only at elevated temperatures and pressures. For example, phenol has been formed
-------
Table III Commercially Important Reactions of Benzene*
(Ayers and Muder, 1964; Erskine, 1972)
r
o
CH = CH
(100%) (97%)
o
-
I
Major Uses
CH--CH = CH?
(88%)
(80%)
Cl-
Cl
Cl Cl
Minor
Catalytic
oxidation
HNO
H g(J
H2S°4
C1
C02H
fc7«\
* "
Uses
Heat
catalysis
reduction
Caustic soda
fusion
(93%)
H-SO,
2 *
Caustic Soda
Fusion
HO
(82Z)
2 CH-CH = CH2
/"-3
CH-
H0~\ U >-OH
* Numbers in parenthesis indicate yields based on benzene starting material.
-------
as a product of autoclave heating of benzene with 20% NaOH at 300-400°C
with oxides of vanadium (Ayers and Muder, 1964). Commercially, benzene is
hydrolyzed to phenol by first placing a good leaving group on the ring
(e.g. - Cl). i{|
C. Oxidation
1
Benzene can be oxidized to a number of different products, but
usually catalysts and/or elevated temperatures and pressures are necessary.
For instance, benzene is not affected by ordinary oxidizing agents (e.g.,
permanganate or chromic acid) until rigorous conditions are realized, in
which case, complete oxidation to water and carbon oxides occurs. Com-
mercially, benzene is catalytically oxidized to maleic anhydride and other
by-products using air or oxygen at elevated temperatures with vanadium oxide
catalyst. Both benzoquinone and phenol have been isolated from benzene
that has been exposed to air and elevated temperatures (410-800°C) without
catalysts.
Boocock and Cvetanovic (1961) have studied the reaction of oxygen
atoms, produced by mercury photosensitized decomposition of nitrous oxide,
with benzene. They reported the formation of a "non-volatile material
probably largely aldehydic in character" as well as smaller amounts of phenol
and carbon monoxide.
Smith and Norman (1963) examined the oxidation of benzene and toluene
I i
with Fentori's reagent (Fe and H_0»). The suggested reactive species is the
hydroxyl radical and the resulting products from benzene are phenol and biphenyl
(dimerization).
-------
D. Photochemistry
As can be seen in Figure 1, benzene does not absorb light directly
o
in appreciable amounts at wavelengths longer than 280 nm (2800A) when dissolved
in cyclohexane. However, slight shifts in wavelength absorption might be
expected in more representative environmental media Ce.g., in water or
adsorbed on particulate matter). For example, Chien (1965) measured the ultra-
violet absorption spectra of liquid benzene under 1 atm. of oxygen (see Figure 2).
In contrast, benzene vapor in air only absorbs light at 275 nm or less (Noyes
et^ al., 1966). Since the ozone layer in the upper atmosphere effectively filters
out wavelengths of light less than 290 nm, direct excitation of benzene in the
environment is unlikely unless a substantial wavelength shift is caused by the
media. However, in water or soil, indirect excitation may be possible due to
the presence of sensitizers. Several investigators have studied the photolysis
of benzene with <290 nm light and these studies will be briefly reviewed.
Benzene has been photolyzed with <290 nm light both in the vapor
phase and in oxygenated aqueous solution. Luria and Stein (1970) exposed an
oxygenated aqueous solution of benzene to 253.7 nm light and reported the
formation of 2-formyl-4H-pyran (I). However, with convincing spectra data
and synthesis, Kaplan et al. (1971) have identified the photoproduct as
0
hv
cyclopentadiene-carboxaldehyde (II). Jackson and co-workers (1967) photolyzed
benzene vapor (10 Torr) at 147 nm after the benzene was first degassed under
vacuum. Gaseous products formed in the reaction included acetylene, ethylene,
-------
5b
4.0
2.5
1.5
Anthracene
COO
Solvent: cyclohenane
j
w
Benrene \
ri
\
v^ i\
Ivenf cyclohexane \
i i
1
1
. L.
1
1
1
--
... .
; i '
i 1
1
: I' i
. i !
I -.--..
i
i
.. L
!
i
21*0
2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 4400 4600 4800
jyavelength (A)
5000
Figure 1. Electronic Absorption Spectra of Benzene, Naphthalene,
Phenanthrene, Anthracene, and Naphthacene (Silverstein^
and.Bassler, 1968, p. 166) Permission granted by
John Wiley & Sons, Inc.
?200 2400 2600 JJOO 3000 3300 HOO 3400 3800
WAVELENGTH. X
Figure 2. Ultraviolet absorption spectra
(1-cm. path length, 1 atm. of
oxygen) of: (1) 2,2-dimethylbutane;
(2) 2-methylpentane; (3) 2,3-
dimethylbutane; (4) n-heptane, 2,2,4-
trimethylpentane (isooctane) and 2,4-
dimethylpentane; (5) 2,3-dimethylpentane;
(6) cyclohexane and methylcyclohexane;:
(7) octene-1; (8) chlorobenzene; (9).
cyclohexene and cyclooctene; (10) benzene;,
(11) cuemen and toluene. (Chien, 1965),.
Reprinted with permission from ^
J. Phys. Chem., 6£, 12, 4317-25.
Copyright by the American Chemical Society.
-------
methylacetylene, vinylacetylene, and butene. However, the major product is
a polymeric material. Irina and Kurien (1973) photolyzed benzene vapor in
the presence of oxygen with 253.7 nm light. They isolated mucondiaidehyde
(HCOCH=CHCH=CHCHO) when organic solvents were used as trapping agents; phenol
was isolated with water in the trap. Matsuura and Omura (1974) have reviewed
sev.eral studies where atomic oxygen photochejlically generated from various
- '^ss^sf' : . .
.'>? -y^1 ' ' ' '
sources reacted with benzene to form phenol? 'Atomic oxygen is generated from the
photodecomposition of nitrogen dioxide, which is frequently found in high con-
centrations in heavily polluted air^Alt^ii3||er and Bufalini, 1971). ,
$p r^ & ' "'- 'i '
Because benzene is frequently^ detected in heavily polluted air
" '-' ,''.->V
samples, it has been photolyzed under' simulated smog conditions. Although
reaction conditions have varied considerably from researcher to researcher
(all use >290 nm light), benzene has been characterized as one of the least
"' ,$"' '' "''
reactive hydrocarbons (in terms of hydrocarbon loss) along with acetylene
and paraffinic hydrocarbons (Altshuller and Bufalini, 1971). However, some
reaction does occur. Laity f-t^ al^. ;(197$^ iirfeported that benzene disappeared
$5£. -**j:-i
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IV. ENVIRONMENTAL EXPOSURE FACTORS AND MONITORING
t
A. Benzene Contamination from Commercial Sources
Benzene is produced in huge quantities in the United States. Over ten
billion Ibs. were produced in 1973 (U.S. Tariff Commission, 1974). In: 1970,
benzene was the second largest primary organic compound in terms of production
and production value (ethylene first) (SRI, 1971). For the most part, benzene
is used for synthesis of other raw materials for the commercial organic* chemical
industry (see Figure 3). Quantities of benzenes consumed in producing the major
by-products for the period 1961-1971 are tabulated in Table IV.
The amount of benzene released to the environment during production,
storage, transport, and raw material uses is unknown. However, some estimates
can be suggested.
1. Production
Benzene can be derived from coal or petroleum, but the majority
(88%) is now produced from petroleum sources. Only small amounts of benzene
'i
are present in crude oil so reforming is usually necessary. Three gallons of
crude light oil (55-70% benzene) are generated for each ton of, coal carbonized
r . .
to coke and this light oil is the major source of coal benzene. ., Table V lists
the benzene capacities, geographical location and name of the large commercial
petroleum derived benzene producers as of January 1, 1972. Table VI presents
the- benzene capacity derived from coke production. Figure 4 depicts the geo-
graphic distribution of the production plants (Erskine, 1972). From the map in
Figure 4, it canrbe seen that a few plants are located along the Mississippi
' "''''
Riverj but the vast majority are located along the Gulf of
along, the Texas coast. :
Benzene is usually stored in steel tanks and shiigp^d in railroad
' '
. . ,
tank cars, tank trucks i 55-gal. returnable and single-trip metal 'drums, and
. ' ' L '- l
10
-------
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r
SUCCINIC ACtO 1 I PCLYESTl%S
1 FtASTICIZJR
TEtPENE ABDUCTS .» ALKYOWSINS 1 PES?ICtDES
AtKYDRIStNS __, I MAi3«-.s» eo» tilNS
POLYESTER RESINS fpLANT GROWTH fECUL*ICtS I
poiPAU PLASTIC17E*',
'[pCLt^nH*-;'.:
-j FIBERS
|_RISINS
MONOflLAMCMTS
Figure 3 Commercial Uses of Benzene and Benzene Derivatives
(Chemical Origins and Markets. Stanford Research
Institute, 1967, pp. 18-19.)
-------
Table IV, Benzene Consumption (millions of pounds)
(Erskine, 1972)
K>
Other
Year
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
% of Total
(1971)
Aniline
110
123
139
152
175
214
202
236
299
357
297
3.5
Cyclo-
hexane
404
477
604
851
1162
1349
1332
-, 1586
1710
1363
1311
15.6
Detergent
DDT Alkylate
125
122
131
90
103
103
76
101
90
43
43
0.5
195
221
202
224
250
286
273
303
298
317
323
3.9
Dichloro-
benzene
70
85
87
80
67
73
73
86
76
85
94
1.1
Ethyl-
benzene
1489
1587
1703
2057
2415
2653
2695
3066
3894
3770
3709
44.2
Maleic
Anhydride
109
110
111
155
179
237
235
254
281
301
325
3.9
Phenol
757
795
890
1083
1207
1325
1345
1526
1712
1803
1610
19.2
Non-fuel
Uses Total
520
299
498
147
375
272
331
-15
412
544
676
8.1
3780
3820
4365
4843
5930
6511
6562
7136
8775
8584
8385
100
-------
Table V Petroleum Based Benzene Production Plant Location
and Capacity (Erskine, 1972)
Company Location
Allied Chemical
Amerada Hess Corp.
American Petrofina, Inc.
Ashland Oil, Inc.
Atlantic Richfield Co.
Atlantic RichfieId-Union Oil
Charter International Oil Co.
Cities Service Co., Inc.
Coastal States Gas Prod. Co.
Commonwealth Oil Refining Co.
Crown Central Petroleum Corp.
Dow Chemical Co.
Gulf Oil Corporation
Marathon Oil Co.
Mobil Oil Corp.
Monsanto Co.
Pennzoil United, Inc.
Phillips Petrol. Co.
Shell Oil Co.
Skelly Oil Company
Southwestern Oil & Ref. Co.
Standard Oil Co. of Calif.
Standard Oil Co. (Ind.)
Standard Oil Co. (N.J.)
Standard Oil Co. (Ohio)
Sun Oil Co.
Tenneco, Inc.
Texaco, Inc.
Union Carbide Corp.
Union Oil Co. of Calif.
Union Pacific Corp.
Winnie, Texas
St. Croix, Virgin Islands
Big Spring, Texas
Ashland, Kentucky
Tonawanda, New York
Houston, Texas
Wilmington, California
Nederland, Texas
Houston, Texas
Lake Charles, Louisiana
Corpus Christi, Texas
Penuelas, Puerto Rico
Houston, Texas
Bay City, Michigan
Freeport, Texas
Alliance, Louisiana
Philadelphia, Pa.
Port Arthur, Texas
Detroit, Michigan
Texas City, Texas
Beaumont, Texas
Alvin, Texas
Shreveport, Louisiana
Sweeny, Texas
Guayama, Puerto Rico
Deer Park, Texas
Odessa, Texas
Wilmington, California
Wood River, Illinois
El Dorado, Kansas
Corpus Christi, Texas
El Segundo, Calif.
Texas City, Texas
Baton Rouge, Louisiana
Baytown, Texas
Port Arthur, Texas
Marcus Hook, Pa.
Corpus Christi, Texas
Tulsa, Oklahoma
Chalmette, Louisiana
Port Arthur, Texas
Westville, N.J.
Taft, Louisiana
Lemont, 111.
Corpus Christi, Texas
Benzene
Capacity
(10° Ibs.)
37
169
220
441
184
323
118
132
59
184 .
73
1176
37
220
294
(514)
242
279
44
44
440.
551
88
162
808
478
37
147
294
88
59
110
625
441
441
110
110
110
88
110
331
257
367
220
66
Total Jan. 1, 1972 10,817
Future Total (11,332)
13
-------
Table VI Coke-Oven Operators Deducing
Coal-Derived Benzene (Erskine,
"v.-. v.'.'
Company
Armco Steel Corp.
Bethlehem Steel Corp.
C.F. & I. Steel Corp..
Interlake, Inc.
Ling-Temco-Vought, Inc.
Mead Corporation
Northwest Industries, Inc.
Republic Steel Corp.
U.S. Steel Corp.
Location
Middletown, Ohio
Houston, Texas
Bethlehem, Pa.
Lackawanna, New York
Sparrows Point, Maryland
Pueblo, Col.
Toledo, Ohio
Aliquippa, Pa.
Chattanooga, Tenn.
Woodward, Ala.
Lone Star, Texas
Cleveland, Ohio
Gladsden, Ala.
Youngstown, Ohio
Clairton, Pa.
Geneva, Utah
Benzene Capacity
January 1. 1972
(10° Ibs.)
Total
778.3
14
-------
Also ,
2 plants-Puerto Rico
1 plant-Virgin Island;
Figure 4 Geographical Location of Benzene Production Plants
Derived from petroleum
* Derived from coal
-------
barges. Because benzene is fairly volatile, it is likely that some release
to the environment takes place during production, storage and transport. Although
the quantity is unknown, it seems reasonable to assume that no more than 1% of the
total production is lost in commercial production, storage and transport, especially
because of the economic incentives to reduce losses. This loss would amount to
approximately 80 million pounds in 1971 centered in relatively specific
geographical areas.
2. Losses from Commercial Uses
As Figure 3 and Table IV demonstrate, the major commercial appli-
cation of benzene is as a raw material for by-product synthesis. The efficiencies
of these synthetic processes vary from approximately 100% yield (reduction of
benzene to cyclohexane) to a low yield of 57% (oxidation of benzene to maleic
anhydride) (Erskine, 1972). If one assumes that the difference between 100% yield
and the reported yield (Erskine, 1972) is the amount of benzene potentially lost
to the environment, the upper limit calculation in Table VII is possible. Of
course these losses are much higher than is actually the case since some of
the benzene is probably recycled or converted to a by-product and losses due ;
to secondary synthetic steps are not excluded from the calculation. 'The "other
non-fuel uses" include consumption for synthesis of anthraquinone, benzene
hexachloride, chlorobenzene (other than for DDT, aniline, and phenol), diphenyl,
nitrobenzene (other than for aniline), cumene (other than for phenol), and
ethylbenzene (other than for styrene). Only extreme small amounts of benzene
are used for solvent purposes. The quantity in this other non-fuel category
is determined by difference (Erskine, 1972) and the losses vary depending
upon the processes. Thus no loss calculation was made. However, this
category only amounts to 8% of the total benzene consumption, at least in 1971
(in some years this figure is a minus number because it is determined by
difference see Table IV).
16 -.'.- . ;
-------
Table VII Upper Limit of the Amount of Benzene
Lost from By-Product Manufacturing
Facilities (106 Ibs.) in 1971
By-Product
Ethylbenzene
Phenol
Cyclohexane
Maleic Anhydride
Detergent Alkylate
Aniline
.Dichlorobenzene
DDT
Other Nonfuel Uses
Benzene
3709
1610
1311
325
323
297
94
A3
676
Consumption
% of Total
44
19
15
4
4
3
1
1
8
100% minus
% Yield *
3
18
0
43
20
7
15
40
Amount of Benzene
Unaccounted for
111
290
0
140
65
21
14
.17
--
658
* The yields used are for overall yields to the various by-products. Some of these
processes (e.g., phenol) are more than one step and, therefore, the losses may be
not only benzene but also the intermediate compounds (e.g., chlorobenzene or cumene
with phenol production).
17
-------
Astwith production, the losses during synthesis of by-products
are not evenly distributed geographically. Table VIII lists the major by-
product producers along with the product manufactured, the capacity of the plants
in terms of benzene required, and the geographical location. The]latter is also
depicted in Figure 5. The locations marked by an asterisk in Table IX indicate
sites where the by-product producer also has a benzene production plant. In those
instances where the by-product producer and benzene manufacturer are located in the
1
same city, the possible losses due to transport are considerably lower.. By compar-
/
ing Figure 4 with Figure 5, it appears that the by-products are manufactured some-
t
what more in the northeast (closer to the market) while the benzene feed stock is
-------
Table VIII. By-Product Manufacturing Plants
(Erskine, 1972)
Company
Allied Chem. Corp.
American Cyanamid Co.
American Petrofina, Inc.
Ashland Oil, Inc.
Baychem Corp.
Clark Oil & Refining Co.
Coastal States Gas Prod. Co.
Continental Oil Co.
Cos-Mar, Inc.
Dow Chemical Co.
E.I. DuPont de Nemours
El Paso Natural Cas Co.
first Mississippi Corp.
Gulf Oil Corp.
Hoppers Co. , IncV
"~ -''"-*": :..'"' _._";*?'- *%"
Marathon Oil Company'- ;"-'r-::.~"n5?-v
-- _;.. '-...-*:'--- - X**-£yV7-
Kbosanto Co. . - * "
Petro-Tex Chem.- Corp. - -'
Phillips Petroleum Co
Location
Houndsvllle, W.V.
Bound Brook, N.J.
Ulllon Island, W.V.
*
Big Spring, Texas
*
Ashland, Kentucky
Hew Martlnsville, W.V.
Blue Island, 111.
*
Corpus Christ!, Texas
Baltimore, Maryland
Carville, Louisiana
*
Freeport, Texas
Midland, Mich.
Beaumont, Texas
Gibbet own, N.J.
Odessa, Texas
-Paecagoula, Miss.
** '' '
Donaldaonvllle, Ga.
Philadelphia, Pa.*
Port Arthur, Texas*
Brldgeville, Pa.
Texas City, Texas*
.Alvin, Texas*
St. Louis, Missouri
Houston, Texas
Sweeny . Texas *
Guayaha, P.R. *
Product (Benzene required 10 Ibs.)
Aniline
35.9
53.8
358.6
89.7
179.3
121.0
62.8
Cumene
222.67
74.2
103.9
7.42
259.8
334.0
155.9
475.0
'i
Cyclohexane
46.7
200.6
200.6
331.3
Detergen
79.4
89.3
Ethyl-
68.1
503.4
567.7
264.9
208.1
427.7
1067.7
Maleic
27.9
47.5
146.6
69.8
Phenol
236.6
(continued)
-------
Table VIII.(continued)
ro
o
Reichhold Chemicals, Inc.
Rubicon Chemicals, Inc.
Shell & Common. Chem. , Inc.
Shell Oil Co.
Sinclair-Koppers Co.
Skelly Oil Co.
Standard Oil Co. (Calif.)
Standard Oil Co. (Ind.)
Standard Oil Co. (N.Y.)
Standard Oil Co. (Ohio)
Sun Oil Co.
Tenneco Inc.
Texaco Inc.
Union Carbide Corp.
Union Oil Co. of Calif.
Union Pacific Corp.
U.S. Steel Corp.
Uitco Chem. Co., Inc.
Totals, January 1, 1972
Elizabeth, N.J.
Morris, 111.
Tuscaloosa, Ala.
Geismar, La.
Penuelas, P.R.
Deer Park, Texas *
Tor ranee, Calif.
Port Arthur, Texas
El Dorado, Kansas *
El Segundo, Calif. *
Richmond, Calif.
Texas City, Texas *
Bay town, Texas *
Port Arthur, Texas *
Corpus Chrlstl, Texas *
Fords, N.J.
Port Arthur, Texas * .
Hestville, N.J. *
Institute, W.V.
Seadrift, Texas
Ponce, P.R.
Nederland, Texas
Corpus Chrlstl, Texas *
Seville Island, Pa. .,{ V
Wilraington, Calif.
46.6
;''"'"'- ':'~"~
645.6
" 59.4
59.4
74.2
37.1
185.6
103.9
341.4
::' -'- -
_
2493.9
181.9
242.7
242.7
200.6
84.0
^c , -^
1731.1
79.4
23.8
59.5
257.4
J.1_!. -
15.9
347.2
196.8
408.8
681.3
70.4
5338.8
41.9
83.8
30.7
55.9
504.0
151.0
387.7
* Location where the
benzene production
by-product producer has a
plant at the same site.
-------
Figure 5. Geographical Location of Benzene By-Product
Manufacturing Plants
-------
Releases of benzene in motor vehicle emissions are somewhat more
difficult to estimate. Both evaporation of the fuel and benzene emissions
with the exhaust can be appreciable sources. In an urban envirbtiitneilt^ approxi-
mately 20% of the transportation hydrocarbon emissions (in termsv';(df;;grams per
vehicle mile for passenger vehicles) are due to evaporation, thj$fjf||$rtK 'coming
from exhausts (Wendell e_t al., 1973). The total emissions of K||!|ifl||i^«rittS ,
from transportation sources is estimated to be 29,400 million pf^|fi||i|ij&971
(about ,55% of the total hydrocarbon emission) (Council on EnvirbnteefrE Quality,
1973). Benzene is found in varying amounts in gasoline (regular 1.35% by wt.,
premium 0.81%, API fuel 0.12%; Sanders and Maynard, 1968). 'When the gasoline
evaporates, the relative proportion of benzene may increase or decrease depending
upon the volatility of all the gasoline components (benzene is one of'the more
volatile components of gasoline; Mair, 1964). However, if it is assumed that
benzene is 1% of the gasoline vapors and gasoline vapors are 20% pf the total
annual motor vehicle emissions (29,400 x 10 Ibs. x .20 = 5,880 x 10 Ibs.),
the total annual (1971) emission of benzene from gasoline evaporation is 58.8
million pounds. 'Benzene consists of 2.15% by volume of the hydrocarbon emissions
from a reciprocating engine (Schofield, 1974). On a weight basis, the percentage
would amount to approximately 4%, since the lower molecular weight hydrocarbons
(methane, acetylene, ethylene) make up more than 50% of the hydrocarbon emissions.
Thus, the annual benzene emissions from motor vehicle exhausts would''amount to
approximately 940 million pounds in 1971. The total benzene motor vehicle
emissions in 1971 would be approximately 1,000 million pounds and would be
geographically distributed very similar to population.
*American Petroleum Institute
22
-------
Table IX summarizes benzene emissions from both conmercCji^Xprodtiction
,' - * i * .*.-'
ViU>Vi,V ("
and use and non-production sources. These sources are -probably t^itaaipr 'sources,
'. - " "- :'~f:^ >' ' ' "
but other sources may be significant. For example, the other 455? of the.hydro-
_';:(i
carbon emission from non-transportation sources may contain considerable amounts
of benzene, especially fossil fuel combustion processes (e.g., power plant). The
quantities involved are unknown.
Table IX Comparisons of Benzene Emissions for 1971
Source Geographic Location Quantity
(106 Ibs.)
Commercial benzene Mostly the Southwest "80
production, storage (assumed 1% of
and transport total production)
Commercial benzene Southwest and Northeast 658
use (upper limit based
on reaction yields)
Oil Spills Oceans and Rivers 22-24
Motor Vehicle Similar to Population , 1,000
Emissions Distribution
C. Environmental Monitoring and Analysis
1. Analysis Techniques
Techiques for determining benzene in air, water and blood have
been reported. Usually some type of preconcentration step is required when
measuring low concentrations, but a number of researchers have used direct
analysis. For example, Bradley and coworkers (Bradley and Franzel, 1970;
Bradley et^ aJL , 1972) used laser Raman spectroscopy for detection and identi-
fication of benzene down to approximately 20 ppm in water. The technique has
23
-------
the advantage of no sample work-up and it can be used in the field. However,
because of its low-sensitivity, application is probably limited to, monitoring
high concentration effluents. >(
Harris e_t aU (1974) have investigated the potential for? a direct,
aqueous injection technique using combined gas chromatography-mass spectrometry
i
(GC-MS). Although benzene was not one of the compounds examined, the technique
' -i
is generally good to between 1-50 mg/jl (ppm) of water, which is not sufficient for
relatively clean water.
Bramer et_ al. (1966) devised a continuous flow instrument for
determining relative amounts of trace organics in chemical plant effluents
based upon the ultraviolet (UV) absorption of the aqueous solution. A, mercury
discharge, lamp (mostly 253.7 nm) was used as the light source. The mejthod was
sensitive to 50 ppb benzene, but since many other compounds besides benzene
absorb UV light, the method is not specific for benzene.
s
In order to study animals subjected to 5000 ppm benzene, Fati
(1969) used a technique which required the injection of 1 yfc of b^opd directly
into a gas chromatograph. Concentrations of 0.03 mg/1000 ml (ppm) of blood
could be detected.
Direct analysis of air samples has also been used by Altshuller
and coworkers (Altshuller and demons, 1962; Altshuller and Bellar, 1963). They
used a direct injection (3 ml air sample) technique with gas chromatography to
analyze benzene in ambient air samples and in synthetic photochemical "smogs".
The flame ionization (FI) detector used with the gas chromatograph was sensitive
enough for detection of individual aromatic hydrocarbons in the 0.05 - 1 ppm
range in synthetic smogs (Altshuller and demons, 1962) and in the 0.005 to 4 ppm
range in ambient air samples (Altshuller and Bellar, 1963).
24
-------
Preconcentration or extraction techniques used for detecting
low concentrations of benzene in air or water samples have varied considerably
as is noted in Table X. Both liquids and solids have been used as adsorbents
for concentrating the sample. The increased sensitivity derived from this
approach is accompanied by greater work-up and handling times. Since handling of
the sample increases the potential for losses, Wasik and Tsang (1970) have suggested
the addition of predeuterated benzene before processing of the sample. By measuring
the deuterated to undeuterated ratio after concentration, an accurate concentration
of benzene in the sample can be determined. This technique has not been used in
any of the preconcentration techniques.
For water samples, the most sensitive technique for benzene is
the inert gas stripping method of Novak et^ al_. (1973). In fact, the method was
so sensitive that benzene and chloroform were found in relatively pure drinking
-4
water (benzene -10 mg/X.). The authors suspect, and have some proof t;hat the
compounds are adsorbed from the laboratory atmosphere (chloroform is adsorbed
from the laboratory atmosphere to concentrations of several ppm in water within
1 hr.) (Novak et al., 1973). This emphasizes the need for careful handling of
the sample during manipulation in order to prevent contamination. The carbon-
chloroform extract procedure used by Gordon and Goodley (1971), U.S. EPA (1972),
and Friloux (1971) is a common procedure for isolating enough material for
qualitative determinations. However, the procedure provides only approximate
quantitative information because the adsorption and desorption efficiencies
are usually not determined. For quantitative information, the efficiencies
of adsorption on the carbon, losses during drying of the carbon, efficiency
of the chloroform extraction, and losses during solvent reduction would have
to be determined.
Both silica gel and activated charcoal have been used as room
temperature adsorbents of benzene in air samples. With silica gel, a prefliter
of molecular sieves is commonly used to remove the water vapor. Whitman and
25 ;' ' ,' ',.
-------
Table X. Preconcentration Techniques for Analysis
of Benzene, in Air and Water Samples
Reference
Zarrelta « a_l. (1.967)
Novnk e£ a^. (L973)
Gordon and Goodley (1971)
U.S. EPA (1972)
Frlloux (1971)
U.S. EPA (1974)
Dambrauskas and Cook
(1963)
Bencze (1965)
Whitman and Johnston (1964)
Sherwood (1971)
Elklns e£ al. (1962)
Koljkowsky (1969)
Cooper ec_
-------
Johnston (1964) have demonstrated that water vapor can have a drastic effect
on benzene adsorption on silica gel. This problem is eliminated when activated
charcoal adsorbent is used since the affinity of water .for activated charcoal
(or carbon) is very low. Thus, in moist atmosphere?, activated charcoal has
been recommended for sampling compounds that are weakly adsorbed on silica
gel (Buchwald, 1965).
Cold trap concentration of benzene from air samples followed by
direct injection into a gas chromatograph appears to be the most sensitive
technique. However, the procedure has the disadvantage that the analyst has
only one sample with which to work. In contrast, the charcoal or silica gel
adsorption procedure followed by solvent extract provides the analyst an
opportunity to store the sample and to inject numerous aliquots into the gas
chromatograph.
2. Monitoring Data
The available ambient monitoring data for benzene are summarized
in Table XI. The information provides some suggestive evidence (but not proof)
of the environmental contamination sources of benzene. For example, the EPA
analytical study of finished waters (US EPA, 1972) drawn from the Mississippi
River also examined the organic waste effluents from sixty industries which are
discharging into the Mississippi. Fifty-three organic chemicals ranging from
acetone to toluene were identified in eleven plants. Benzene was not detected
thus suggesting a contamination source other than industrial water effluents.
Pilar and Graydon (1973) studied the concentration> of benzene
and toluene at seventeen sampling stations and took samples continuously at
one-hour intervals for nine days. Based upon (1) the ratio.of toluene to
benzene, (2) the distinct maxima for both toluene and benzene at 0700, 1500
and 2100 hrs., and (3) the relative concentrations at various sampling stations,
the authors concluded that there was little doubt that the benzene contamination
was linked to automotive transportation. The.toluene-benzene ratio found in
27
-------
Table XI Ambient Monitoring Data for Benzene
Reference
Gordon and Goodley (1971)
U.S. EPA (1972)
Friloux (1971)
Novak et_ al. (1973)
Williams (1965)
Smoyer et al. (1971)
s
Neligan e_t al. (1965)
Altshuller and Bellar
(1963)
Lonneman et^ al. (1968)
Grob and Grob (1971)
Stephens (1973)
-------
Pilar and Graydon (1973)
Type of Sample
Water and mud
Finished water
Finished water
"Polluted" and
"pure" drinking
water
Ambient air
Ambient air
Ambient air
Ambient air
Ambient air
Ambient air
Ambient air
- - .
Ambient air :
Geographical
Location
Lower Tennessee River
Carrolltdn Plant,
New Orleans
U.S. PHS Hospital
Carville, La.
Prague, Czechoslovakia
Vancouver, Canada
Vicinity of solvent
reclamation plant
Los Angeles basin
Downtown Los Angeles
Los Angeles basin
Zurich, Switzerland
Riverside,. ..California
-Toron tby. Canada >' p^"1 ' ;
Sampling*
Method Used
CCE liquid-liquid
extract
CCE
Inert gas
stripping
Cold trap -
GC column
Grab sample
Cold trap -
firebrick
Grab sample
Cold trap -
glass beads
Charcoal trap -
carbon disulfide
extract
Cold trap -
GC column
.Cold trap -
GC column
Analysis*
Technique
GC-MS
Preparative GC,
GC, GC-MS
rapid heating
into GC
direct injection
into GC; MS, IR
rapid heating
into GC
direct injection
into GC
rapid heating
into GC
GC-MS
GC-FI
GC-FI
-GC-FI
Quantities
Detected
Not reported
Not attempted
"trace" ppb-ppm
range
-0.1 ppb
1-10 ppb
23 ppm
.005-. 022 ppm (V/V)
0.015-0.06 ppm (V/V)
aver. 0.015 ppm
highest 0.057 ppm
(V/V)
0.054 ppm
0.007-0.008 ppm
aver. 0.013 ppm;
highest 0.098 ppm
*CCE - carbon chloroform extract; GC - gas chromatography; FI - flame ionization; IR - infrared spectrometry; MS - mass
spectrometry.
-------
Toronto air was higher than in automotive exhaust. This high ratio in ambient
air has also been noted by Lonneman e_t al. (1968). Several possible explanations
were suggested by Pilar and Graydon (1973) including (1) the fact that gasoline
vapors have a relatively high toluene-benzene ratio suggesting the possibility
'' , ";!'
of direct evaporation as a source, (2) Inapplicable automotive exhaust monitoring
data for the Toronto situation, and (3) physical or chemical;changes between
emission and air sampling.
'.tf.* ..'
''--f ,'-11'.,'
, .Jv'iy (VI V .
. .A';, ;.
29
-------
V. ENVIRONMENTAL FATE
A. Degradation or Alteration Processes
1. Biological Transformation of Benzene
a. Microbial Degradation . '.^'V:^. ;
While the microbial degradation of bferizener; :fti£Jf|$^n the
subject of much recent research and review, attention haa;
on the enzymatic mechanisms of degradation and their re]
malian systems (e.g., Smith and Rosazza, 1974) rather than
of biodegradation under conditions approximating environment^ l-'eji
Nonetheless, the information that is available indicates that benzene is
susceptible to attack by a variety of microorganisms utilizing pathways
analogous to those of a number of aromatic compounds. While such degradation
probably occurs under certain environmental conditions, the rates of degrada-
tion in the natural environment cannot be extrapolated from the available data.
(i) Degradation by Mixed Cultures of Microorganisms
The effect of mixed microbial cultures on benzene
has been studied primarily to determine if benzene can
or will be degraded under waste treatment plant condi-
tions. These studies indicate that benzene can be
. degraded but that the rates of such degradation vary
considerably depending upon the incubation period and
previous acclimation of the microorganisms. The results
of these experiments are given in Table XII.
30
-------
Table XII: Degradation of Benzene by Mixed Cultures of Microorganisms
Benzene cone.
Reference
Bogan and
Sawyer
(1955)
Source of
Microorganisms Adaptation
Activated sludge none
Incubation [Activated
Time sludge cone.]
5 days (standard
dilution BOD
technique)
Oxygen
Consumed
1.9% of theoretical
Domestic sewage
14 days (10 ppm up to
100 ppm then 48 hrs.
with no exposure to
test compound)
5 days (standard
dilution BOD
technique)
6 hr (Warburg)
50-100 ppm
[-3000 ppm]
2.4% of theoretical
3.3% of theoretical
Marion and
Malaney
(1963)
Activated sludge
none
24 hr (Warburg)
160 hr (Warburg)
500 mg/1
[2500 mg/1]
500 mg/1
[2500 mg/1]
about equal to
endogenous control
1.1-1.3 times
endogenous control
Malaney
(1960)
Activated sludge
aniline as sole carbon 190 hr (Warburg) 500 mg/1
source (20 day feeding [2500 mg/1]
program)
2 times endogenous
control
Chambers Soil, compost, or
et al. mud from a petro-
(1963) leum plant waste
lagoon (predomi-
nantly
phenol as sole carbon
source
28 hr (Warburg)
100 mg/1
1.6 times endogenous
control
0.2 times phenol
control
-------
Interpretation of the results obtained la' very
difficult. The sludge used by Marion and Malaney (1963)
was not washed before placement in the Warburg flask and,
therefore, the carbon sources in the sludge "weiee available
to the microorganisms. In several of thep24 hr test runs,
the oxygen uptake measured with benzene was less than the
control, suggesting inhibition. In the longer runs, only
a slight difference was noted between the control and
i
benzene. The results of Bogan and Sawyer (1955) have the
endogenous rate subtracted from the reported oxygen con- .
sumption. Again only a small increase in oxygen consumption
is noted and, of the five hydrocarbons studied, only
^-butylbenzene was more resistant to biochemical oxidation.
Chambers et^ al. (1963) concluded that with their phenol
adapted seed, the "benzenes were oxidized, with difficulty
or not at all." In fact, the benzene rate was similar to
v
such compounds as 1,3,5-trichlorobenzene and 1,3,5-
trinitrobenzene which one would expect to be fairly per-
sistent. Perhaps the safest conclusion from the four studies
in Table XII is that benzene may be biodegradable, but at a
very slow rate.
In a study of the biodegradability of chlorinated
analogs of hydrocarbons, Okey and Bogan (1965) developed
an adapted sludge that was capable of growing on benzene
as the sole source of carbon (50 mg/O. The sludge utilized
about 45% of the total substrate (benzene) COD in 10 hours.
32 ."';'.
-------
Thus, it has been demonstrated that benzene can serve as
a carbon and energy source for a culture enriched on
benzene and derived from a treatment plant activated
sludge.
Biodegradation of hydrocarbons in marine water
relative to fresh water is seriously limited by the
scarcity of nitrogen and phosphorus (Atlas and Bartha,
1973). Since benzene is a component of crude oil, under-
standing its fate in marine waters, where most large oil
spills take place, is very important. Unfortunately, no
mixed culture studies with benzene in sea water have been
attempted. However, with fifteen microorganisms isolated
from sea water or sediment, Bartha (1970) only found one
organism (Brevibacterium) capable of utilizing benzene for
growth. In a similar study by Perry and Cerniglia (1973),
where a large number of microorganisms were isolated and
the number of organisms capable of growth on the substrate
was used as criteria for biodegradability, the aromatics,
in general, were found to be more recalcitrant than any ,
other hydrocarbon except for cycloalkanes. Art assessment
of benzene degradation under marine conditions should
consider the results of Walsh and Mitchell (1973). These
authors showed that 0.1 ppm benzene inhibits ch^motaxis
(chemical communication resulting in attractio^'ijif a
''if'- * .'"
microorganism to a test substrate) by 50% in oofcile marine
.'W- >:'"..
Pseudomonas . The importance of the effect is .lOaknown since
' ''
*'£ e ' ' . i"
the concentration of 0.1 ppm is considerably highel than
'. ' »S« '..""/'">. ' ',.:.','
-------
what would be expected in marine waters, but the inhibi-
tion may have immediate effects on the rate of degradation
or long-term effects on the diversity and population of
marine organisms. ?<
(ii) Degradation by Pure Cultures of Microorganisms
From the studies listed in Table XIII, it can be
concluded that benzene can be degraded by a number of
v'
microorganisms. In some instances, the organism can use
benzene as a carbon and energy source. However, pure
culture studies provide very little degradation rate
information because they are considerably removed from...con-
ditions experienced in nature. Rarely is the test substrate
(benzene) the only source of carbon. Competition between
different microorganisms for the available nutrients is
ignored in pure cultures. The concentration of the test
substrate is considerably higher than would occur In nature
thus questioning whether the necessary enzymes that are
Induced at the high test concentrations would ever be induced
tinder natural conditions. The work by Cofone at al. (1973)
suggests that the Induction period with Cladosporium resinae
>i
is slow (22 days) even at high concentrations (10 ;oi benzene
overlayed on 100 ml of sterile salts solution). Nevertheless,
> T. ', j
. .'.,'f '"
the pure culture studies, combined with information obtained
' '. ' .' --"XT
with cell-free extracts, do provide a great deal bf1 Inforoia-
. .''.
tion about the pathways of benzene degradation by j , ';
1 . . ' ' v ,,
microorganisms.
34
-------
XIII. Pure Cultures of Microorganisms
Which Degrade Benzene
Reference
Cofone et al., 1973
Smith and Rosazza,
1974
"
"
-
Bartha, 1970
Hogn and Jaenicke,
1972
Gibson ct al. , 1968
Gthson et al.. 1970
Claus and Walker, 1964
"
Marr and Stone, 1961
Organism
Cladosporlum resinae
Penicilltum chrysogenum
Cunn inghame 1 la
blakealeeana
Gliocladium deliquescens
Streptomyces sp.
Cunninghamella bainieri
Brevibacterium (K)
Moraxella B
Pseudomonas putlda
Pseudomcmas putlda 39/D
(mutant strain)
Achromobacter sp.
Pseudomonas sp.
Mycobacterium rhodochrous
Pseudomonas aeruginosa
Source
Jet Fuel
Culture Collection*
n ii
M it
It H
.,
Sea water and
sediments
River mud (by
enrichment culture
technique vlth
benzene)
Soil (by enrichment
culture technique
with toluene)
M
..
ii
Soil (by enrichment
culture technique
with benzene)
M
Incubation
Period
34 daya
1-3 days'1"
"
tl
..
not specified
60 mln.
40 mln.
30 hrs.
ISO mln.
ISO min.
120 mln.
120 mln.
Prior
Acclimation
_
24 hrs on
fresh soybean
meal-glycose
medium
"
tt
..
.
_
_
_
-
_
Metabolites Identi-
fied or Proposed
_
Phenol and two
unknown phenols
u
>
>
"
_
cis-l , 2-Dihydroxy-
1,2-dihydrobenzene
Catechol
cis-l, 2-Dlhydroxy-
1 , 2-dihydrobenzene
Catechol
cis-l, 2-Dihydroxy-
1,2-dlhydrobencene
.
-
Catechol
+ benzene not used as sole source of carbon
* selected for known ability to metabolize aromatic compounds
35
-------
(ill) Pathways of Microbial Breakdown of Benzene1
1
(a) Ring Attack
The primary step in the degradation of benzene
^ by moat bacteria seems to involve a dioxygenase'enzyme .
li
leading to the formation of catechol via cis-1,2-
dihydroxy-l,2-dihydrobenzene. Such a scheme is outlined
in Figure 6.
02
NADH
Benzene
Hypothetical cis - 1,2-Dihydroxy- Catechol
Dioxetane 1,2-dihydrbbenzene
Figure 6: Microbial Degradation of Benzene to Catechol
(modified from Gibson, 1971; HOgn and
Jaenicke, 1972) Courtesy of Springer-Verlag.
Such a pattern is indicated'by the results of
Gibson and coworkers (1968, 1970) and Hbgn and Jaenicke
(1972). Using 1802> Gibson et_.al> (1970) showed ttiat both
oxygen atoms added to benzene are derived from atmospheric
oxygen. In addition to dioxygenase modification, evidence
by Smith and Rosazza (1974) seems to indicate that mono-
oxygenase systems also operate in certain microbial systems,
resulting in the hydroxylation of benzene to phenol. Although
phenol has long been proposed as an intermediate in the oxi-
dation of benzene by some microorganisms (Kleinzeller and
36
-------
Fencl, 1952), phenol has only recently been isolated
from cultures grown in the presence of benzene (Smith
and Rosazza, 1974).
(b) Ring Cleavage
Although a number of microorganisms have the
ability to modify benzene, no organism is able to cleave
the unsubstituted benzene ring directly. Instead,
cleavage occurs with the metabolism of catechol which
can be derived from benzene either by dioxygenase dihy-
droxylation or by the further hydroxylation of phenol.
Bacterial ring cleavage of catechol may proceed by either
ortho or meta fisshion as illustrated in Figure 7.
cis, cij>-Muconic Acid
ro u
lU 2 cc-OH-Muconic semialdehyde
Figure 7: Ortho Fission of Catechol by Pseudomonas
putida and Moraxella Iwoffii and Meta
Fission of Catechol by a Pseudomonas sp.
(adapted from Chapman, 1972). :
Both types of cleavage involve the addition of
molecular oxygen through a non-heme ion dioxygenase
(Dagley, 1972). With ortho cleavage, catechol is converted
37
-------
to g-ketoadipic acid, whereas meta cleavage has been
*
shown to result in the formation of acetaldehyde' and
pyruvic acid (Chapman, 1972). The details of these
pathways are illustrated in Figure 8.
ORTHO
'COOH
c-o
'COOH
,COOH
B-Ketotdipic acid
CH.
META
'OH
COOH
Acetaldehyde
COOH
C=O
Pyruvlc acid
Figure 8: Benzene Ortho Fission Pathways by Pseudomonas
putlda and Moraxella Iwoffii and Meta Fission
by a Pseudomonas sp. (adapted from Chapman, 1972).
(b) Mammalian Metabolic Pathways
Since the initial demonstration of benzene
conversion to phenol by mammals C>chultzen and Naunvn, 1867),
a number of studies have been conducted in an attempt to
delineate the pathways involved in the mammalian metabolism
of benzene and related aromatic compounds'.' With the infor-
mation available on the metabolism of benzene by-;;rats and
38
-------
rabbits, Gibson (1971) described the pathways of mammalian
benzene metabolism illustrated in Figure 9. Although
benzene oxide has not yet been conclusively demonstrated
as a benzene intermediate and the formation of trans,-
trans-muconic acid from catechol is still not completely
understood, the metabolic scheme as presented does seem to
account for what is currently known about the fate of
benzene in mammals.
S-CH2-CH-COOH
NH-CO-CH3
Phenylmercapturlc Acid
T
S-Glu-Cys-Gly
Cl
W-^c
Conjugates
S-(l, ;'-Dihydro-2-hydroxyphenyl)glutathione
t
"e ^.Benzen
o
Conjugates
OH
OH
Uxepln Phenol
Hydroxydihydroquinone
t
OH
H "-^ H
Benzene-l,2-oxide trans-l,2-Dlhydro- Catechol
1,2-dihydroxybentene
:2H
trans, trans-
Muconlc Acid
Conjugates
Conjugates
Quinol
dihydroqulnone
Figure 9: Proposed Pathways of Mammalian Benzene Metabolism
Based on Studies with Rats and Rabbits
(Adapted from Gibson, 1971) Courtesy of CRC Press.
(1) In Vivo Studies
Most of the general pathways presented in
Figure 9 were proposed on the basis of early in vivo studies
using rabbits. Porteous and Williams (1949a) administered
39
-------
benzene orally to rabbits at a dose of 500 tng/kg. On
analyzing urine samples, about twenty percent of the dosage
was accounted for as conjugates of phenol, catechol, dihy-
f
droquinone, and hydroxydihydroquinone, with phenol conjugates
comprising about half of the total conjugates recovered.
In addition, small amounts of free phenol' and muconic acid .
were also,detected. On the basis of this study and experi-
ments using related aromatic compounds, Carton and Williams
(1949) postulated the following.pattern of benzene metabolism:
,[ 1,2-dihydro-l,2-dihydroxybenzene]
20%
Benzene
Quinol
Quinol
Conjugates
Pheno
Hydroxyquinol
Phenol
Conjugates
v.
Catechol
Conjugates
Hydroxyquinol
Conjugates
Figure- 10: Primary Metabolic Pathways of Benzene in
Rabbits as Proposed by Carton and Williams (1949)
In addition to. the pathways identified through the analysis
of metabolites, indicated by solid lines in Figure 10,
Porteous and Williams (1949b) proposed an alternate pathway
for the formation of.catechol involving 1,2-dihydro-l,2-
dihydroxybenzene. This supposition was based on a comparison
40
-------
of dihydroquinone:catechol ratios which were 1:1 with
benzene and 10:1 with phenol as the substrate. The high
ratio with phenol metabolism identified dihydroquinone as
the primary metabolite, since it would be expected that
the ratio would not change if phenol were the sole inter-
mediate in the production of catechol from benzene (Porteous
and Williams, 1949b). Parke and Williams (1953a and b)
attempted to pursue this hypothesis with more quantitative
14
analysis of C-benzene. However, because they were unable
to synthesize trans-1,2-dihydro-l,2-dihydroxybenzene and did
not detect muconic acid in phenol fed rats, they erroneously
suggested that the benzenediol was the sole precursor of
muconic acid (parke and Williams, I953b).
With oral administration of benzene to
rabbit.s at doses of 500 mg/kg, Parke and Williams (1951)
demonstrated that muconic acid excreted in ;the urine was
the trans,trans isomer and not the cis,cis form which
might be expected on the basis of stereochemical considera-
tions and which is found in microbial ortho cleavage
(see Figure 7). The trans,t_rans_ isomer formation was
subsequently confirmed in studies using radiolabelled
benzene (Parke and Williams, 1953a). The details of forma-
tion of trans,trans-muconic acid are still not understood
(Gibson, 1971).
41
-------
Parke and Williams (1953a) also proposed
r
phenylmercapturic acid as a minor metabolite (0.4-0.7%
of dose) of benzene in rabbits. In rats administered
benzene (1000 mg/kg) by stomach tube, a precursor of
phenylmercapturic acid, which converted to, phenylmercapturic
acid on treatment with l.Syil HC1, was identified in the mice
(Knight and Young, 1958). A similar mercapturic acid pre-
cursor identified as N-acetyl-S-(l,2-dihydro-2-hydroxyphenol)
cysteine was found in the urine of rabbits given intra-
peritoneal doses of 0.5 ml benzene (Sato e_t £d., 1963).
i
A more significant aspect of the study by Sato 'and coworkers
(1963) was the tentative identification of l,2-
-------
preparations, the metabolism of benzene to phenol and
phenol conjugates was shown to be enhanced by pretreat-
ment with benzene. This stimulation of benzene metabolism
involved increased amino acid incorporation into microsomal
protein and was suggestive of enzyme induction (Snyder et al_.,
1967). Recently, Gonasum and coworkers (1973) have impli-
cated a mixed function oxidase and the binding of benzene
to cytochrome P-450 in the metabolism of benzene to phenol
by mouse liver microsomes.
The in_ vitro metabolism of trans-1,2-
dihydro-l,2-dihydroxybenzene has been studied by Ayengar
and coworkers (1959) using a partially purified enzyme
from rabbit liver. After incubation for thirty minutes,
catechol was identified as the sole metabolic product
which is consistent with Figure 9. The enzyme involved
was named diol-dehydrogenase and the oxidation to catechol
was coupled to the reduction of nicotinamide-adenine
dinucleotide phosphate.
A major advance in the understanding of
benzene metabolism was the synthesis of benzene oxide and
its subsequent use in in vitro metabolism by Jerina and
coworkers (1968). In this study, rabbit liver microsomes and
the soluble fraction were incubated with benzene oxide for
thirty to sixty minutes. The results of this work are
summarized in Figure 11.
43
-------
S-U^-dihydro^-hydroxyphenyD-glutathlne
>K
lutathlme -/
Soluble Fraction
microsomes or soluble
Oxepin * =; Benzene Oxide 8olu^le fraction^ tranB-l.Z-Dihydro-l^-dihydroxybenzene fra*tioi> catechol
>l
nonenzymatic
Phenol
Figure 11: The In.. Vitro Metabolism of Benzaae, Oxide
Using Rabbit Liver Microsomes and Soluble
Fraction (adapted from Jerina et al., 1968)
Although the metabolites of benzene oxide, coincide with
those of benzene and thus implicate benzene oxide as an
intermediate in the metabolism of benzene, benzene oxide
itself is highly unstable and has not yet been isolated
in the metabolism of benzene. Although no .metabolites of
oxepin were found by Jerina and :coworkers .(1968), oxepin
is known to be in equilibrium with benzene oxide and is
thus included in the pathway diagrams. The conversion
of benzene oxide to phenol was conclusively shown to be
nonenzymatic but catalyzed by acid, protein, simple
peptides, or acetamide (Jerina e£ al-, 1968).
44
-------
The role of benzene oxide in benzene
metabolism, while not conclusively demonstrated, is
nonetheless generally accepted. In this respect,
benzene metabolism seems analagous to the metabolism of
various other aromatic hydrocarbons which also involve
arene oxide intermediates (Jerina et^ al., 1970; Kaubisch
et^ a^., 1972). In addition, the bone marrow toxicity of
benzene might be related to the formation of benzene oxide
because the latter is an electrophile with alkylating
properties (Daly e± _al., 1972). General reviews of
arene oxide formation have recently appeared supporting
the role of benzene oxide in benzene metabolism based on
the common metabolites of the two compounds, particularly
on the formation of trans-l,2-dihydro-l,2-dihydroxybenzene
and the mercapturic acid precursor (Jerina, 1974; Jerina
and Daly, 1974).
(3) Kinetics of Benzene Metabolism and
Elimination
For the most part, the kinetics of benzene
metabolism in mammals has not received detailed attention.
14
Parke and Williams (1953a) administered C -benzene to
rabbits by gastric intubation at doses ranging from
340 mg/kg to 500 mg/kg and attempted to monitor all
metabolites over a thirty to seventy hour period. A
partial summary of their results is presented in
Table XIV.
45
-------
Table XIV: Metabolic Fate of a Single Dose of C-labelled Benzene
Administered to Rabbits by Gastric Intubation, 30-70 Hours
After Dosing (Parke and Williams, 1953a) ,
43
Nature of .metabolite
Benzene exhaled unchanged
Respiratory CO-
Phenol*
Catechol*
Qulnol*
Hydroxyquinol*
trans-trans-Muconic acid
-Phenylmercapturic acid
(Urinary radioactivity)
Metabolized benzene in tissues and
faecest
Total accounted for
* These phenols are excreted conjugated
t About 0.5% of dose in faeces
// Benzene in expired air + urinary radioactivity.
% of dose (average)
44.5 in expired air
32.6 in urine
23.51
2.2
4.8
0.3
1.3
0.5J
(34.5) : .
About 5-10 in body
77 (79)#
Although most of the dose was eliminated by the third day,
."' .', *-'
elimination measured as urinary metabolites dropped pre-
cipitously to only 0.3% in the fourth through seventh days
14
after benzene administration. Measurements of C-labelled
a ."
CO, were riot uade after the third day, thus a potential shift
£, -r , "-
,:b. -
in excretory pathways cannotgbe determined.
Most of the more recent studies on benzene
metabolism have been concerned with monitoring urinary
phenol or benzene elimination from the lungs. Bakke and
Scheline (1970) administered benzene by stomach tube at
doses of 100 mg/kg and 1000 mg/kg to rats and found that
only 3.1-3.7% was excreted as urinary phenol after 48 hours.
This low level of urinary phenol was inconsistent with the
46
-------
above work of Parke and Williams (I953a) on rabbit as
well as the study by Cornish and Ryan (1965), which
indicated that rats metabolized 23% of an intraperitoneal
dose of benzene (400 mg/kg) to urinary phenolic compounds.
Measurements of unchanged benzene in expired
air and urinary phenol have been suggested as techniques
for determining levels of occupation exposure to benzene
(Sherwood, 1972). In measuring respiratory elimination in
man, Sherwood found evidence for a two compartment system
of elimination, the first having a half life of 2.5 hours
and the second of about 22 hours (see Figure 12).
i or
10
0
5
a
00
II 1
2 JMOUHS
yfj -22 HOURS
£ AFTER OCCUP1IIONAL
-Q. /' Cxposunt
- '32 HOURS
10 20 30 40 SO 60
HOURS AFTER EXPOSURE
Figure 12: Elimination of Benzene in Exhaled Breath of
One Subject After Unspecified Experimental
and Occupational Exposure of About 4 hours.
(Sherwood, 1972) Courtesy of Pergamon Press Ltd.
47
-------
This type of elimination pattern is indicative pf rapid
elimination of benzene from the lungs to the alveolar
air with less rapid removal of benzene from the body
tissues.
Hunter and Blair (1972) have correlated per-
cent body fat to percent of benzene excreted vs. urinary
phenol after exposure to benzene vapor, as illustrated
in Table XV.
Table XV: The Factors and Times of Post-Exposure
Observations, Benzene Doses and Excretions
in 5 Adult Males Exposed to the Vapours of
Benzene on Single Occasions (Hunter and
Blair, 1972)
Body
Subject fat
number (X wt)
1 8.3
2 , 13.0
3 16.0
4 18.2
5 19.7
Concentration
of benzene
In teat
atmosphere
(ug/D
63
309
133
340
328
328
88
103
294
405
103
Post-exposure
time of
observation
(hr)
24.7
49.8
30.8
31.9
48.0
30.5
38.2
28.9
29.5
23.0
43.5
Dose
Benzene
(mg)
33.0
118.0
184.0
116.0
117.0
75.0
167.0
99.0
217.0
58.0-
52.0
Weight of
benzene
excreted
i as phenol
(mg)
16.7
70.0
; 139.3
85.0
90.7
64.4
137.6
71.3
170.3
49.1
45. :i
Excreted
benzene as
percentage
of dose
<* wt)
50.6
59.4
75.7
73.3
77.6
85.9
82.4
72.0
78.5
84.6
87.1
From this, it was postulated that benzene accumulation
in the body probably occurs in the fat deposits, although
Parke and Williams (1953a) noted only 2.6% of a benzene
dose in rabbit fat two days after exposure. In further
48
-------
contrast to studies in nonhuraan mammals, Hunter and
Blair (1972) calculated that only 12% of a benzene dose
is eliminated unchanged in expired air in man.
(c) Degradation by Plants
Benzene has recently been isolated from pine-
apple (Flath and Forry, 1970). However, the potential
role of plants in the degradation of benzene has not been
extensively investigated in the United States. Jansen
14
(1964) found that benzene- C can be synthesized from
14
ethylene- C in avocados. In a subsequent study exposing avo-
14
cados to benzene- C vapor, 25-28% of the benzene was absorbed
14
by the plant and 0.004-0.007% was metabolized to C02. In
addition, volatile and nonvolatile substances other than
benzene were noted (Jansen and Olson, 1^69). Similar
results have been recently reported by Durmishidze and
coworkers (1974), who reported that potatoes, apples,
tomatoes, quince, pepper, lemons, grapefruit, tung, and
14
bananas absorb C-benzene from the atmosphere at benzene
levels of 10 mg/1. Most of the benzene is converted to
muconic, fumaric, succinic acids, and phenylalanine with
only a small amount being oxidized to (XL.
Benzene degradation by plants has received con-
siderable attention in the U.S.S.R. Durmishidze and
Ugrekhelidze (1967) found that tea, laurel, grape, and
corn roots absorbed radiolabelled benzene, which was
subsequently metabolized to C0? in all parts of the plants,
14
Tea plants administered C-benzene through the roots were
49
-------
found to convert 16% of the total dose to organic and amino
r ,
acids. In this experiment, the following metabolic pathway
was proposed: Benzene -» Phenol -* Catechol * 'jo-Benzoquinone
-» Muconic acid (Durmishidze and Ugrekhelidze,' 1969). Grapes,
during all stages of growth including germination, are
reported to oxidize C-benzene to CO- and other aliphatic
compounds (Tkhelidze, 1969). More recently,;peas admin-
14
istered C-benzene through the roots have metabolized
benzene using copper containing enzymes including o-
diphenol oxidase (Ugrekhelidze and Chrikishvili, 1974).
In summary, there is a strong indication that
plants may perform a major role in the degradation and
synthesis of benzene in the environment.
2. Chemical and Photochemical
The available studies on the photochemical degradation or
alteration of benzene under environmental conditions (wavelengths of light
>290 run) have been previously reviewed in Section III. No other chemical
reactions, iwhich might take place under environmental conditions, have been
noted in the literature.
B. Transport
Transport of benzene from the point of release to various points
in the environment is not well understood. In fact, only Pilar and Graydon
(1973) have presented convincing evidence that the source of benzene in air
in correlat'ed to automotive emissions. However, from the physical properties
of benzene >some projections of benzene distribution in the environment are
50
-------
possible. The relatively high water solubility (1780 mg/fc at 25°C) and
vapor pressure (95.2 ram Hg at 25°C) are perhaps the most important parameters.
From these parameters, Mackay and Wolkoff (1973) have calculated that the
half-life of benzene, undergoing constant mixing and at less than saturation
concentrations in a square meter of water, would be 37 minutes. In compar-
ison, ri-octane's half-life would be 3.8 seconds; DDT, 3.7 days; and dieldrin,
723 days. However, because of its fairly high solubility in water, benzene
will probably be washed out of the atmosphere with rain and thus a continuous
cycling between air and water would occur.
Neely et al. (1974) have demonstrated a relationship between
octanol-water partition coefficients and bioconcentration potential in fish.
Although the logarithm of the partition'coefficient for benzene (2.13) is
outside the region treated by Neely .et al. (1974), the calculated bio-
concentration factor, nineteen, would suggest little potential for
bioaccumulation.
In summary, although little is known about the -transport of
benzene in the environment, based on physical properties the compound should
be quite mobile with a low bioaccumulation potential.
51
-------
VI. EVALUATION
A. Summary
Benzene is a major synthetic organic chemical intermediate which
is probably being produced at a rate of about ten billion pounds per year.
Over the period from 1963 to 1973, benzene production more than doubled.
However, because benzene is derived primarily from petroleum products and
the petroleum'market is currently in a state of flux, it is difficult to
estimate the continued growth potential of benzene. For the most'part,
production sites are localized in areas rich in raw materials; petroleum
based production concentrated along the Texas Gulf and coal based pro-
'duction in the northeast and south central area. Commercial use of benzene
is similarly localized but the amount used in the northeast seems considerably
more than the amount produced, thus requiring transport of benzene from the
Texas Gulf to the northeast.
Benzene is also a significant constituent of gasoline (about 1%
by weight) and automotive exhausts (^ 4%). Unlike the chemical intermediate
usage, benzene release from these sources is much more diffuse and probably
approximates population density distribution.
Although precise estimates of benzene release are difficult to make,
approximate calculations indicate benzene release into the environment approaches
1.8 billion pounds annually. Total motor, vehicle emissions make up well over
half of this release. Release from commercial use probably does'not exceed
30% of the total. Other sources are relatively insignificant: production
a little over 2% and oil spills under 1% of total release.
52
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The relatively high volatility and water solubility of benzene
would indicate that significant amounts of benzene could reside both in the
atmosphere and in aquatic systems. Although no direct studies have been
encountered on the bioaccumulation of benzene, benzene's octanol-water
partition coefficient does not indicate a high potential for bioaccumulation
in fish. . . . -t
Due to the high degree of resonance stabilization in the unsub-
stituted aromatic ring, benzene is a relatively stable hydrocarbon. Under
environmental conditions, the rates of hydrolysis and oxidation are probably
negligible. Although photochemically initiated reactions may be a factor in
benzene degradation, these processes also seem to proceed at a relatively
slow rate and their significance is difficult to assess with the information
currently available.
The biological stability of benzene under environmental conditions
is similarly difficult to estimate. A variety of pure cultures of microorganisms
have been shown to possess enzymatic systems capable of metabolizing benzene
at concentrations much greater than would be expected in the environment.
However, with mixed cultures in the standard 5 day BOD test or using Warburg
respirometry technique, only a slight increase in the respiration rate was
observed. When the microbial respiration rates of benzene are compared to
presumably stable analogs of benzene, such as 1,3,5-tricHlorobenzene, it seems
that while benzene may be susceptible to microbial attack, its rate of degra-
dation by microorganisms would be slow at best. Mammals and plants are also
capable of metabolizing benzene, but the ultimate degradation - i.e., breakdown
to carbon dioxide and water - is slight. Nevertheless, the alteration of benzene
to phenolic conjugates by plants may be a significant environmental process for
the removal of benzene.
53
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The available monitoring information supports the experimental data
-'
on the chemical and biological behavior of benzene, indicating that benzene is
' ' ' ','.*'<
at least moderately persistent and a potential contaminant of both air and .f
water. However, benzene monitpring data is incomplete at best.. With the excep-
tion of the air monitoring done by Pilar and Grayden (1970), fixed-interval
measurements in the same area over extended periods have not been made. Thus,
most monitoring studies are of little use in determining the major source(s)
of benzene pollution. Similarly, only Novak and coworkers (1973) offer
reliable quantitative measurements of benzene water contamination. However,
even with these limitations, the monitoring information does suggest that
benzene may be, a widespread air and water contaminant in the low ppb range.
Also, the monitoring data suggest that benzene is partially resistant to
normal drinking water treatment procedures. While the work of Pilar and Grayden
(1970) indicates automotive exhaust as a major source of benzene air contamination,
the relatively high level (23 ppm) found by Smoyer and coworkers (1971) near a
solvent reclamation plant suggests that industries handling benzene may also
be significant sources of contamination.
B. Recommendations
Given the type of information currently available on the biological
degradation of benzene, little can be concluded about benzene's persistence.
At the presumably low (ppb) background levels found in the aquatic environment,
substrate inhibition would not be expected and benzene degradation may proceed
by the pathways previously described. Equally probable, the enzyme(s) required
to hydroxylate benzene may not be active at low benzene levels or in the
presence of other suitable carbon sources. These possibilities could be easily
54
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examined using C-labelled benzene at low (10-100 ppb) concentrations in mixed
or pure cultures of microorganisms commonly found in fresh water, salt water,
or sewage treatment plants. The effects of temperature and alternate substrates
should also be examined. Similarly, the importance of benzene adsorption by
vegetation should also be examined in the low ppm range.
While the methods for the quantitative determination of benzene in
air seem satisfactory, the only quantitative method used for benzene in water
is the inert gas stripping technique of Novak and coworkers (1973). The tech-
nique of gas stripping followed by concentration on a gas chromatographic column
(EPA, 1974) appears to be a desirable method for determining low concentrations
of benzene ;Ln water, although no benzene was detected in the water examined
(EPA, 1974). The reliability and limits of detection of the techniques probably
should be examined further.
j_
More extensive benzene monitoring should be considered a necessity.
Besides the obvious need for more extensive air and water analysis, monitoring
might be most productively concentrated near benzene production and by-product
manufacturing plants in order to quantitate the losses. The 1% loss during
benzene production used in this report may well be conservative, especially
for coke-based production where considerable loss could take place during stoking
of the ovens. The calculated losses (100% minus % yield of final product)
during by-product manufacturing are upper limits since the loss is assumed to
to be entirely benzene. Much of the actual loss during certain operations
may occur between the intermediate and final product stage. Detailed moni-
toring studies would, no doubt, provide more realistic estimates of benzene
loss from manufacture and use.
55
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«. reUtive environ^! ha,ara ««» *«- -ta.in.tion reouire,
the intention of in^ation on reiease t. *. environs, persistence in
consiae.ations . «
benzene eolation ^ aiso ,e ^ on consi^ations o£
e£fecta * >_ as «U as in^ion on other environmental contaminants
_ ^ ,e e,ally i^tant. ~re, it ~» W note, that « reUti.
1088M o£ ben,ene .o.ecte, in tHia report are confieo by «nitoring aata
PoSslH1ity ,or elective re^aia! action (1.... el-ation o£: ,en«ne iosses
from automotive emissions) seems rather remote.
56
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