Environmental Sources of
Benzene Exposure:
Source Contribution Factors
S. Drill
R. Thomas
July 1979
Contra:! Sponsor U.S. Environmental
rrotection Agency
Contrar.tNo.: 63-01-4635
Projscl No.: 1555D
Dcpt.: V/-56
The h'.iTRE Corporation
Me'rek Division
1820 Doiley Madison Soui-sv.rd
McLean, Virginia 24W?
MITRE Technical R >ov!
f/TR-770'i
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ABSTRACT
The National Interim Primary Drinking Water Regulations are
undergoing review. As part of that effort, the health risks associ-
ated with selected organic drinking water contaminants for which
standards were not promulgated in the interim regulations are being
assessed. This study is intended to assist the Office of Drinking
Water, U.S. Environmental Protection Agency, in that effort by iden-
tifying the frequency of occurrence of benzene in the various envi-
ronmental media, characterizing the benzene levels in these media,
and determining the relative benzene contribution of each of these
sources to an individual16 total daily benzene uptake.
ill
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ACKNOWLEDGEMENT
The authors wish to thank Dr. Charles L. Trichilo for his
continuous support and encouragement during the preparation of this
document.
This document was reviewed in final draft form by Dr. Bernard
D. Goldstein, Institute of Environmental Medicine, Mew York University
Medical Center.
iv
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EXECUTIVE SUMMARY
The MITRE Corporation/Metrek Division has been assisting the
Criteria and Standards Division, Office of Drinking Water, U.S. Envi-
ronmental Protection Agency in assessing the adequacy of the Interim
Primary Drinking Water Regulations. Part of this effort has been the
identification of the frequency of occurrence of benzene in the vari-
ous environmental media, characterization of the benzene levels in
these media, and determination of the relative benzene contributions
of each of the pertinent environmental sources to an individual's
total daily benzene uptake.
Benzene is emitted to the environcent from petroleum refineries
and coke ovens, the two major sources of commercial benzene produc-
tion, and from chemical manufacturing facilities, the major avenue of
benzene consumption. Benzene is highly volatile, and there is there-
fore a considerable potential for evaporitive emissions to the atmo-
sphere during production, storage, transport, and use of the com-
pound. Facilities which produce benzene and .its major by-products
(styrene, phenol, and cyclohexane) are primarily located near the
major domestic sources of oil and coal, i.e., in the Gulf Coast
States and the Middle Atlantic States, respectively, and emissions
from these sources will be greatest in these areas. The majority of
benzene transport in the U.S. is between these centers of production
and consumption, and thus, losses during transport are largely re-
stricted to the interconnecting transportation routes. Emissions
from all of these sources in 1971 have been estimated to be as much
as 738 million pounds (42 percent of total quantified U.S. benzene
emissions).
Benzene is a component of gasoline, and motor vehicle emissions
are thought to constitute the greatest source of benzene emissions.
Atmospheric emissions from this source contained an estimated 1 bil-
lion pounds in 1971 (57 percent of total 1971 emissions). Benzene is
also emitted to the environment by evaporation of gasoline during
transfer. Additional losses result froa evaporation of benzene-
containing solvents and from oil and fuel spills.
Data on atmospheric benzene levels are scarce, as there has been
no routine program for monitoring atmospheric pollution by this com-
pound. Reported values range from 3 to 900,000 ^ig/m-*, although
levels at the high end of this range were measured in areas where
production, use, or disposal of benzene was thought to create a local
air pollution problem. A conservative estimate for the national
average urban benzene concentration is 50
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Data on levels on benzene in food are extremely limited*although
benzene has been measured qualitatively in a large number of food-
stuffs. Eggs have been found to contain high levels (1900 Hg/kg) of
the compound. Daily dietary benzene intake has been estimated to be
as much as 250 ug.
Benzene has been detected in b percent of the 113 U.S. water
supplies surveyed in the National Organics Monitoring Survey (NOMS).
The median concentration for all samples ranged from less than 0.1
to 0.2 ng/1. The highest concentration was 1.8 pg/1* Benzene was
detected in four of ten drinking water supplies iu the National Or-
ganics Reconnaissance Survey (KORS). Concentrations in these four
water supplies ranged from 0.1 to 0.3 ug/1.
Inhalation of benzene is the most frequent cause of industrial
benzene poisoning, and thus inhalation has been the most intensely
studied exposure route. At ambient airborne concentrations, up to
80 percent of inhaled benzene may be absorbed by the lungs. However,
studies in which persons were exposed to benzene contrations over
1000 times higher than urban ambient levels revealed a steady-state
absorption rate of about 45 percent. The rate of benzene uptake
via the gastrointestinal tract is believed to be high, although no
conclusive data are available. It has been conservatively assumed,
therefore, that 1CJ percent of the ingested benzene is absorbed.
Dermal absorption is insignificant under ambient environmental con-
ditions.
After inhalation exposure as much as half or as little as 10
percent of the benzene absorbed by the body is excreted unchanged
through the lung. Most of the remainder is excreted as metabolites
in the urine. Metabolism takes place in the liver, and possibly also
in the bone marrow. The major metabolic products are phenol and its
congeners.
The total daily benzene uptake and the percent contribution to
this total uptake from each of these environmental .ources have been
calculated for an adult male in an urban setting. These calculations
are based upon average concentrations in the various environmental
media (air, food, and water), and estimated consumption and absorp-
tion rates for these media and the benzene contained therein. Based
upon the assumptions utilized, air is the predominant source of ben-
zene absorbed by the general populations. This source contributes
more than 65 percent of the total daily benzene uptake at all drink-
ing water concentrations considered. Drinking water contributes less
than 3 percent at benzene concentrations of 10 ug/1, and well below 1
percent at assumed urban ambient average conditions.
vi
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TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES Viii
1.0 INTRODUCTION 1
1.1 Background 2
1.2 Approach 3
2.0 BENZENE INPUT TO THE ENVIRONMENT 4
2.1 Benzene Production, Storage and Transport 4
2.2 Commercial Uses of Benzene 8
2.3 Contamination From Petroleum and Petroleum-
Derived Fuels 9
3.0 ENVIRONMENTAL SOURCES OF BENZENE EXPOSURE 12
3.1 Benzene Concentrations in Ambient Air 12
3.2 Benzene Concentrations in the Diet 16
3.3 Benzene Concentrations in Drinking Water .19
3.4 Benzene Intake From Smoking 22
4.0 ABSORPTION, RETENTION, AND ELIMINATION OF BENZENE
IN HUMANS 23
4.1 Absorption Characteristics 23
4.1.1 Pulmonary Absorption 23
4.1.2 Gastrointestinal Absorption 27
4.1.3 Dermal Absorption 27
4.2 Metabolic Pathways 28'
4.3 Retention Characteristics 30
4.4 Elimination Characteristics 31
5.0 SOURCE CONTRIBUTIONS TO DAILY BENZENE UPTAKE IN
KUMANS 33
5.1 Approach 33
5.2 Basic Assumptions 34
5.3 Estimated Daily Benzene Uptake 34
5.4 Identification of Critical Receptors 41
6.0 REFERENCES 42
vii
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LIST OF TABLES
Table Number Page So.
2-1 Distribution of U.S. Benzene Emissions, 1971 5
2-2 Upper Limit of Benzene Losses from By-Prcduct
Manufacturing in 1971 7
3-1 Benzer.e Concentrations in Air 14
3-2 Atmospheric Benzene Expsoures Attributable to
Major Emission Sources: Number of Persons
Exposed at Various Concentrations 15
3-3 Foods Reported to Contain Benzene 18
3-4 Benzene Concentrations in Drinking Water 20
4-1 Snnmary of Reported Pulmonary Absorption
Rates for Benzene 25
5-1 Basic Assumptions Employed in the Calculation
of Individual Source Contribution Factors 35
5-2 Representative Environmental Benzene Exposure
Levels 37
5-3 Calculation Sequence in Determining Source
Contribution Factors 38
5-4 Estimated Daily Benzer.e Uptake 39
Figure Number
4-1 Proposed Pathways of Human Benzene Metabolism 29
v
iii
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1.0 INTRODUCTION
The Office of Drinking Water (ODW) within the United States
Environmental Protection Agency (EPA) in accordance with the Safe
Drinking Water Act as amended has promulgated National Interim Pri-
mary Drinking Water Regulations for a number of physical, chemical,
biological and radiological contaminants in potable water systems.
These interim standards, which specify maximum contaminant levels
(MCLs) for substances in drinking water, will be replaced by final
Primary Drinking Water Regulations as more definitive information
describing the health risks associated with each contaminant is
accumulated and analyzed.
Because of a paucity of data on the occurrence of various
organic chemicals in drinking water supplies and the associated risks
to human health, and uncertainties over appropriate methods of treat-
ment, the only organic chemicals for which MCLs were specified in the
Interim Primary Drinking Water Regulations were selected pesticides.
In order to be able to specify MCLs for additional organic contami-
nants in the final Primary Drinking Water Regulations, EPA has pub-
lished Special Monitoring Regulations, and in accordance with these
regulations, is conducting a National Organics Monitoring Survey
(NOMS) of drinking water supplier in 113 U.S. cities.
The MITRE Corporation/METREK Division has been assisting the
Criteria and Standards Division, Office of Drinking Water in the
identification of the frequency of occurrence of benzene in the
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various environmental media, characterization of the benzene levels
in these media, and determination of the relative benzene contribu-
tion of each of the pertinent environaentsi sources to an individ-
ual's total daily benzene uptake. The source contribution model
utilized in this study identifies those er.vironmerttal sources afford-
ing the greatest potential for exposure to benzene, enabling the most
effective regulatory action to be initiated.
1.1 Background
Benzene is widely distributed throughout the environment. The
compound is a component of petroleum and light oil produced froQ
coal, and it is produced commercially free both of these sources.
Benzene is also a component of gasoline. Benzene is highly volatile
and therefore the production and use of the conpouni, and of gaso-
line, offer substantial opportunity for atmospheric benzene emis-
sions. Consequently benzene appears to be ubiquitously distributed
in the atmosphere. Benzene has also been detected in a number of
U.S. waterways and community water supplies and in sooe foods.
Because of the multiple exposure pathways, the relative contri-
butions to an individual's daily benzene uptake arising from s-pecific
environmental media are being defined. IP. this way, if benzene
appears to pose a significant health risk as a result of exposure via
daily drinking water intake alone, or if drinking water intake con-
tributes significantly to the total daily benzene uptake, ther. an
intensive review ar.d analysis of the probles will be initiated.
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1.2 Approach
In order to properly assess the health significance of the
ingest ion of benzene contaminated drinking water, it is necessary to
define the contributions to an individual's total daily benzene up-
take from each major source of exposure. These source contribution
factors can be defined in threi successive steps, i.e.,
define and quantify the major environmental sources of ben-
zene exposure,
« determine the absorption/raetaboiisra/retention and elimination
characteristics of benzene in man via each exposure route,
and
estimate total daily uptake of benzene in can, bssed on anci-
ent exposures and absorption/retention characteristics.
By examining the percent contribution to the total uptake from each
route of exposure, one can calculate the source contribution factors
for each type of benzene exposure. In this way, the significance of
benzene exposure via drinking water can be assessed in view of the
other possible exposure routes.
This report defines the percent contribution to the total daily
benzere uptake from all the major environments] sources of exposure.
The report does not, however, consider or evaluate the toxicologf.cal
implications of such benzene uptake. Those instances when critical
data weie insufficient or lacking are pointed out in the text.
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2.0 BENZENE INPUT TO THE ENVIRONMENT
Benzene is emitted to the environment from petroleum refineries
and coke ovens, the two major production sources, and chemical isanu-
factoring facilities; by evaporation of benzene during storage and
transport and during use of bcr.zcr.e as a solvent; and by evaporation
of petroleum-based fuels. Combustion of fossil fuels may also be an
important source of benzene emissions, although the contribution from
this source has not been quantified. Many of the industrial emission
sources are located near the major domestic sources of oil and coal
(in the Gulf Coast and Middle Atlantic states, respectively). The
quantitative and geographical distributions of benzene emissions from
the major quantified emission sources are shown in Table 2-1.
2.1 BenzeneProduction, Storage and Transport
Benzene has been commercially produced from light oil (generated
by the carbonization of coal to coke) sinca 1849 and fron petroleum
since 1941 (Ayers and Muder, 1964). The compound is still derived
from both sources but petroleum currently supplies most of the ben-
zene produced in the U.S. Approximately 92 percent is derived from
this source (Mara and Lee, 1977). As of early 1975, the total capac-
ity of U.S. benzene production facilities was 1.74 billion gallons
(12.7 billion pounds) per year (SRI, 1975). Actual production of
chemical benzene in 1975 was 8.04 billion pounds (USITC, 1977). U.S.-
benzene production capacity was .more than doubled during the decade
from 1963 to 1973 (SRI, 1975).
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TABLE 2-1
DISTRIBUTION OF U.S. BENZENE EMISSIONS, 1971
Origin
Priraary
Geographic Location
Quantity
(106 Ibs.)
Commercial Benzene
Production, Storage,
and Transport
Gulf Coast States,
Middle Atlantic
States
80'
a
By-product
Manufacture
Gulf Coast States,
Middle Atlantic
States
658'
Oil Spills
Oceans, Rivers
23
Motor Vehicle
Emissions
Approximates
Population
Distribution
1000
Total of quantified
emissions
1761
One percent of tot&l 1971 benzene production,
3Upper limit (see Table 2-2).
SOURCE: Adapted frca Howard and Durkin, 1974,
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Although the Compilation of Air Pollution EmissionFactors (EPA,
1973) states that "there are essentially no emissions from petroleum
reforming operations" the high volatility of benzene suggests that
some degree of evaporative loss during production, storage, transfer
and transport is almost inevitable. Benzene is normally stored and/
or transported in steel tanks, 55-gallon metal drums, tank trucks and
barges (Erskine, 1972) and there is a potential for vapor emission
during transfer to and from each of these containers. In addition,
the rupture of a benzene container may result in high local atmo-
spheric benzene levels, the absolute magnitudes of which will depend
upon the extent of benzene loss and local physical conditions. Quan-
titative estimates of the total benzene emissions from these sources
are not available; however, Howard and Durkin (1974) have assumed
that economic constraints on benzene loss would limit emissions to 1
percent or less of the total quantity produced. The majority of ben-
zene production facilities are located near major domestic sources of
oil (in the coastal areas of Louisiana and Texas) and coal (predomi-
nantly in Ohio and Pennsylvania) (Howard and Durkin, 1974); there-
fore, the quantity of benzene emissions associated with production
will be greatest in these areas. Benzene transport is mainly from
the Gulf Coast States to the Middle Atlantic states, and thus, losses
during transport will be largely restricted to the major intercon-
necting transportation routes (Howard and Durkin, 1974; as indicated
in Table 2-1).
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TABLE 2-2
UPPER LIMIT OF BENZENE LOSSES
FROM BY-PRODUCT MANUFACTURING IN 1971
a
By-Product
Styrene
Phenol
Cyclohexane
Maleic Anhydride
Detergent Alkylate
Aniline
Dlchlorobenzene
DDT
All Other Non-
fuel Usesc
Consumption
(106 Ibs.)
3709
1610
1311
325
323
297
94
43
676
8388(7712°)
Percent Upper Limit of
Yield Lossesb (106 Ibs.)
97 111
82 290
100 0
57 140
80 65
93 21
85 14
60 17
658
a
Quantity not accounted for by end-product yield.
Losses may not only be benzene but also process intermediates.
>«
"Includes synthesis of anthraquinone, benzene hexachloride,
chlorobenzene (for use other than as an intermediate for DDT,
aniline, and phenol manufacture), diphcnyl, nitrobenzene (other
than for aniline), cunene (other than for phenol), and ethylbenzene
(other than for styrene); and solvent uses.
JTotal excluding "Other Konfuel Uses".
SOURCE: Adapted from Howard and Durkin, 1974.
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2.2 Commercial Uses of Ben z e n e
Chemical manufacture accounts for most of the benzene used in
the U.S. (more than 7.7 billion pounds, or 92 percent of the total
U.S. consumption, in 1971 [Howard and Durkin, 1974]). The manufac-
turing processes used in the production of benzene-derived chemicals
vary widely in efficiency; 100 percent of the theoretical yield of
cyclohexane is produced, whereas a yield of 57 percent is attained in
maleic anhydride production (Table 2-2), The difference between the
maximum potential yield of these benzene by-products (100 percent)
and the actual yield, has been used to develop an upper bound of 658
million pounds for the 1971 benzene emissions from facilities manu-
facturing the principal by products (Howard and Durkin, 1974; as
shown in Table 2-2).
The geographical distribution of the aajor benzene by-product
manufacturing facilities is not uniform. The majority of these
facilities are located in the Gulf Coast states (24 of the 49 U.S.
manufacturing facilities are located in Texas, Louisiana, Missis-
sippi, and Alabama; 14 of these are at the site of a benzene produc-
tion facility) and the Kiddle Atlantic States (New Jersey, Pennsyl-
vania, West Virginia, and Maryland have 14 such facilities). Texas
alone has 20 such manufacturing facilities (Howard and Durkin, 1974).
Benzene is used to some extent as an ingredient in paint brush
cleaners, paint and varnish recovers, and other multicomponent sol-
vent formulations (Gosselin et si., 1976). The compound is an
8
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excellent solvent for rubber, and has been used as such in rubber
manufacture (Mara and Lee, 1977) and in rubber cements (Ayers and
Muder, 1964). Benzene will be emitted to the atmosphere by evapora-
tion during use of these products, and'may also be emitted to streams
and rivers via disposal of these products in domestic and industrial
wasrewater.
2.3 Contamination from Petroleum and Petroleum-Derived Fuels
Benzene is a component of petroleum and of gasoline and other
fuels which are derived from petroleum (Howard and Durkin, 1974).
Before 1974, most gasoline produced in the U.S. contained less than 1
liquid volume (Iv) percent benzene (1.3 percent by weight), although
concentrations as high as 2 Iv percent were reported (Runion, 1975).
Sanders and Maynard (1968) analyzed regular and premium gasolines and
found them to contain 1.35 and 0.81 percent benzene by weight,
respectively. As the average lead content of U.S. gasoline has de-
creased, however, it has been necessary to increase the benzene con-
centration to maintain the same average octane rating. More recent
estimates (PEDCo Environmental, Inc., 1977) of the average benzene
content of U.S. gasoline range from 1.24 to 2.5 Iv percent.
The concentrations of benzene in U.S. gasolines are limited by
both the refinery process methods used and economic considerations.
Because of the refinery methods utilized, most gasolines produced in
the U.S. contain between 15 and 35 percent aromatic-rich reforaatea,
whereas European gasolines generally contain 85 to 90 percent
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refortnates (Runion, 1975). Furthermore, selective separation of ben-
zene is economically practical, as it offers a much higher return to
the refiner than when benzene is sold as a fuel component (Runion,
1975).
Howard and Durkin (1974) have calculated the total 1971 benzene
motor vehicle emissions based on total hydrocarbon emissions of 2.94
billion pounds. If it is assumed that evaporated gasoline consti-
tutes 20 percent by weight of the total emissions, and benzene con-
stitutes 1 percent of these vapors, then benzene emissions from
gasoline evaporation would amount to 58.8 million pounds. In addi-
tion, benzene constitutes 2.15 percent by volume of the hydrocarbon
exhaust emissions from a reciprocating (piston) engine (Schofield,
1974). This is about 4 percent by weight (Howard and Durkin, 1974).
Therefore, the amount of benzene in the hydrocarbon exhaust emissions
(the remaining 80 percent of the total hydrocarbon emissions) would
be about 941 million pounds, and the total 1971 motor vehicle benzene
emissions would be about 1 billi-rn pounds (Table 2-1). From these
projections, motor vehicle emissions were projected to be the largest
source of atmospheric benzene in 1971. The geographic distribution
of these emissions would vary with traffic density and would there-
fore be approximately the same as that of U.S. population. Evapora-
tion of gasoline during pumping and bulk loading operations will also.
result in atmospheric benzene emissions; however, these emissions
have not been quantified.
10
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Environmental benzene contamination may also result from oil and
fuel spills and from the evaporation and incomplete combustion of
benzene-containing fuels other than gasoline. The total influx of
oil into the oceans from routine discharges from tankers, tanker
accidents, leaks during storage, pipeline breaks, disposal of spent
lubricants, incompletely burned fuels, and untreated industrial and
domestic sewage is estimated to be between 11 and 12 billion pounds
per year (Blutner et al., 1971). Ascuming that the concentration of
benzene in these discharges is the same as the average concentration
in crude oil (0.2 percent by weight, Howard and Durkin, 1974), the
total annual emission of benzene into the oceans is 22 to 24 million
pounds.
11
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3.0 ENVIRONMENTAL SOURCES OF BENZENE EXPOSURE
Although many potential sources of environmental benzene con-
tamination have been identified, monitoring data that would allow
prediction of the extent of the benzene exposure of the general pop-
ulation attributable to these sources are extremely limited. Benzene
levels have been measured in the ambient air and water in a number of
locations throughout the western world and in a small number of food-
stuffs. The results of these measurements can be used to develop
tentative estimates of average ambient environmental Levels and expo-
sure rates.
3.1 Benzene Concentrations in Ambient Air
The ambient concentration of benzene in urban air is estimated
to range from about 4 to 200 Hg/"^; (Altshuller, 1969; Bertsch et
al., 1974; Pilar and Graydon, 1973). This estimate is based on a
very small body of data, as the level of benzene in ambient air is
not routinely monitored. Concentrations of airborne benzene reported
in the literature range from a trace to 900,000 pg/m-* for areas as
widely dispersed as Zurich, Switzerland; Vancouver, Canada; Edison,
New Jersey; and Iberville Parish Louisiana (Grob and Grob, 1971;
Williams, 1965; RTI #9, 1976; RTI #2, 1977). Values at the upper end
of this range probably do not reflect conditions encountered by a
large majority of the population, however, as eany of the reported
atmospheric benzene concentrations were measured in areas where pro-
duction use, or disposal of organic chemicals was thought to produce
12
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a local air pollution problem. A summary of reported benzene levels
in air is presented in Table 3-1.
Mara and Lee (1977) calculated the number of persons exposed to
benzene from each of the major emission sources in selected concen-
tration ranges above 0.1 ppb (0.32 jig/m-*) and the total exposure
(in ppb-person-years) attributable to each source. The results are
shown in Table 3-2.
Schewe (1977) estimated the average atmospheric benzene concen-
trations in four U.S. cities (Dallas, Los Angeles, St. Louis, and
Chicago) based upon estimated automotive emissions, area, and average
wind conditions. The estimated concentrations ranged from 3.0
(Dallas) to 13.8 jig/n^ (Chicago). However, these estimates are con-
tradicted by reported levels in Los Angeles and other cities (Table
3-1), and a more realistic estimate of the average urban value is
about 50 jig/m^. This high benzene concentration is primarily
associated with high levels of motor vehicle traffic.
Evaporative emissions froa gasoline service stations are also
responsible for a large amount of human exposure to atmospheric ben-
zene, through exposure of both nearby residents and customers, espe-
cially those using self-service facilities. Based upon limited data,
Runion (1975) reported that gasoline vapor concentrations to which
service station attendants were exposed were less than 10 ppau
Assuming benzene constituted 1 lv percent of these vapors, thie cor-
responds to a benzene concentration of 320
13
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The use of benzene-containing solvents and the misuse of gaso-
line as a solvent cleaner for machine parts, paint brushes, hands,
etc., probably results in the greatest short-term atmospheric benzene
levels encountered by the general public (Runion, 1975). Limited
testing in an enclosed room with no positive ventilation showed that
when gasoline is used in this way, concentrations of 100 ppra total
hydrocarbons (about. 3200 fig/ra^ benzene) would be reached frequently
in the breathing zone, and momentary peaks-would be as high as 500 to
1000 ppra total hydrocarbons (16 to 32 mg/m-* benzene).
Reclamation of spent solvents may be another source, however
minor, of atmospheric benzene. In May 1970 the Maryland State Health
Department contracted with the Thiokol Chemical Company to collect
and analyze air samples from a small v&lley nenr Elkton, Maryland.
It was believed that higher-Chan-normal concentrations of various
solvents would be found due to the presence of a reclamation facility
in the vicinity (Capurro, 1973). Benzene was found in the "...air of
the valley within two miles of the plant," in "...the blood of people
in the valley," and in water from a nearby creek. A maximum atmos-
pheric concentration of 73,375 ng/m-* was reported.
3.2 Benzene Concentrations in the Diut
According to Mr. Corbin Miles, Chief of the GRAS* Review
Branch of the Food and Drug Administration, exposure to benzene via
Generally regarded as safe.
16
-------
Che diet is not considered to be a problem of the general population
(Miles, 1977). However, benzene has been detected in fruits, nuts,
vegetables, dairy products, meat, poultry, eggs, fish, and several
different beverages (Table 3-3), and is thought to occur naturally
(possibly at a flavor component) in many or all of the foods in which
it is found. Concentrations of benzene have been measured in only a
small number of these foods: butter (0,5 jig/kg; Siek and Lindsay,
1970); cooked beef (2 to 19 |ig/kg; National Cancer Institute, 1977);
eggs (500 to 1900 |ig/kg*; MacLeod, 1976; MacLeod and Cave, 1976);
haddock (100 to 100 ng/kg; Merritt, 1972); and Jamaican Rum (120
US/kg; Liebich et al., 1970), The benzene level in heated lamb, mut-
ton, and veal, and in chicken, is less than 10 fag/kg (Herritt, 1972).
In some cases, ,the concentration of benzene in foods may be af-
fected by food preparation techniques. Chang and Peterson (1977)
found large amounts of benzene in the volatile fraction of boiled
beef and canned beef stev. It has been speculated that the cooking
of meats causes an increase in their benzene content due to the
breakdown of the aromatic amino acids (phenylalaninc and tyrosine)
(FASEB, 1977). However, the benzene concentration ir. nonirradiated
haddock (stored for 14 days) was found to be twice as great as that
in irradiated haddock (stored for 30 days) (Merritt, 1972).
f
Calculated from the fraction of benzene in total egg volatilec
(0.1 to 0.38 percent) and the fraction of volatiles ir. the whole egg
(0.05 percent) for a 50 g egg.
17
-------
TABLE 3-3
FOODS REPORTED TO CONTAIN BENZENE
Fruits
Apple
Citrus Fruits
Cranberry and Bilberry
Currants
Feyoa and Guave
Pineapple
Strawberry
Tomato
Nuts
Filbert (roasted)
Peanut (roasted)
Macademia Nut
Vegetables
Beans
Leek
Mushroom
Onion (roasted)
Paraley
Potatoe
Soya Bean
(cooked)
Dairy Products
Butter (0.5)1!2
Bleu Cheese
Cheddar Cheese
Other Cheese
Meat, Fish and Poultry^
Beef (cooked) (2 to 19)3
Chicken (
-------
It has been estimated that an individual's dietary benzene in-
take from beef, eggs, and rum alone, may be as high as 250 fig/day
(National Cancer Institute, 1977). Of the foods in which benzene
levels have been quantified, eggs are the most significant source;
one egg may contain as much as 100 ug of benzene.
3.3 Benzene Concentrations in Drinking Water
The literature does contain a small number of references to ben-
zene concentrations in drinking water (Table 3-4). Benzene was one
of a number of organic drinking water contaminants identified in U.S.
cosaunity water supplies in the National Organics Monitoring Survey
(MOMS) of the U.S. Environmental Protection Agency (See Table 3-4);
MOMS Phase I; Phase II; Phase III). The majority of water supplies
tested were located in urban areas. The nedian benzene concentration
was less than 0.2 H8/l« Benzene was detected in only about 6 percent
of the 113 water supplies surveyed. These results essentially veri-
fied the drinking water benzene concentrations reported In the earli-
er National Organics Reconaissance Survey (U.S. Environmental
Protection Agency, 1975). Benzene was detected in 4 of 10 water
supplies surveyed, in concentrations ranging froa 1.0 to 3.0 pg/1.
An analytical study of tap water derived fro:: the Mississippi
River compared chemicals in the water with substances in waste efflu-
ents of 60 industries discharging wastes into the river (U.S. Envi-
ronmental Protection Agency, 1972). A total of 53 organic chenicals
were detected in the effluent from 11 of the plants monitored.
19
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Although a trace of benzene was found in the tap water, it was not
detected in the effluent from any of the facilities, suggesting a
source of contamination other than the industrial waste.
Dovty et al., (197S) thermally extracted low molecular weight
organi.cs from water samples obtained at the intake of a Kew Orleans
area municipal water treatment plant, in the effluent from the clari-
fier before chlorination, and at the tap. Values or various organics
were reported as relative percent abundance in a gas chromatogram.
Absolute concentrations were not determined. The samples tcken from
the Mississippi River at the plant entrance had a relative percent
abundance of a combination of benzene, carbon tetrachloride, and
dichloroethane (which were inseparable chromatographically) of 12.17
while the value for this same combination from the clarifier effluent
was 3.26 and from New Orleans tap water was 36.61. The high relative
abundance of this mixture in tap vater was apparently the result of
chemical disinfection using chlorine and aaaonia. Commercially
bottled artesian water and deionized, charcoal-filtered tap water
processed by a commercial filter unit, were also" sampled and ana-
lyzed. The relative percent abundance of benzese was 16.16 in the
bottled artesian water and 2.17 ia the deionizec charcoal-filtered
water.
Samplings of the effluent fro'a five benzene production and/or
consumption facilities revealed concentrations iron less than 1.0 to
179 jig/1 benzene in the effluent from the plants. However, theae
21
-------
concentrations soon dissipated, as samples from downstream receiving
waters had lower benzene concentrations, ranging from less than 1.0
to 13.0 jig/1 (Batteile-Colunbus Laboratories, 1977)*
3.4 Benzene Intake From Smoking
One source that could be of significance to selected individuals
is the vapor phase of tobacco smoke* The quantity of benzene in one
AO ml pull of cigarette smoke is 6.1 |ig (Newsome et al., 196S).
Assuming 15 pulls per cigarette, an individual smoking one pack of
cigarettes each day would inhele 667«95 rog of benzene each year from
smoking alone.
22
-------
4.0 ABSORPTION, RETENTION, AND ELIMINATION OF BENZENE IN HUMANS
Benzene can be absorbed into the body after inhalation, inges-
tion, and, to some extent, dermal contact. Approximately half of the
absorbed benzene is rapidly eliminated as unchanged benzene via the
pulmonary route, and a small amount of benzene is eliminated in the
urine. The remainder is metabolized to a number of different com-
pounds, or retained at various sites. Benzene is retained for the
longest time in the fatty tissues and bone marrow*
Metabolism of benzene takes place pricarily in the liver{ mainly
producing phenolic compounds. The toxic effects associated with ben-
zene exposure are thought to be caused by one or more of these meta-
bolic products. The metabolites conjugate with glycine, sulfuric
acid, and glucuronic acid, and are subsequently eliminated in the
urine. The following sections describe the primary absorption,
retention, and elimination mechanisms for benzene.
4.1 Absorption Characteristics
Inhalation of benzene vapors is the predominant cause of benzene
poisoning and is therefore the subject of most phsrmacokinetic
studies. Benzene is rapidly and efficiently absorbed from the lungs
and presumably also from the GI tract. Denial absorption is an
insignificant route of uptake under ambient environmental conditions.
4.1.1 PulmonaryAbaorptipn
Because of the high vapor pressure of benzene (100 cm Hg at
26.075°C [Ayers and Muder, 1964J) most incidents of human benzene
poisoning in the workplace have been attributed to inhalation (NIOSH,
23
-------
1974). Therefore, most of the research on benzene absorption has
focused on uptake from the lung. A summary of the reported pulmonary
benzene absorption rates is given in Table 4-1.
Determinations of the rate of pulmonary benzene absorption have
been based upon human exposures to airborne concentrations ranging
from 80 to 19140 mg/m^. These concentrations are at least three
orders of magnitude higher than ambient atmospheric levels. Under
the conditions of these studies, absorption rates varied from 20 to
68 percent, although values found in the older literature are as high
as 85 percent (Srbova et al., 1950). The mean absorption rate for
benzene, based on the results of the eight studies reported in Table
4-1, is about 45 percent.
The rate of pulmonary absorption, at least at these intake
levels, is dependent upon the duration of exposure, and is presumably
also dependent upon the concentration of benzene in the inhaled air.
Srbova and coworkers (1950) reported that 81 percent of the benzene
in inhaled air containing 306 ing/ur* of the compound was absorbed
through the lungs of one subject after 5 minutes of exposure, whereas
the absorption rate declined to 52.5 percent after 15 minutes, and
remained at approximately this level thereafter. In similar studies
with additional subjects (Srbova et al., 1950; Noraiyaraa and Nomiyaraa,
1974b), absorption rates continued to decline very slowly, reaching
an apparent steady state after 2 to 3 hours. This decrease in ab-
sorptive efficiency is thought to be due to increasing saturation of
the blood and tissues with benzene (Srbova et al., 1950; Nomiyaaia and
24
-------
Table 4-1
SUMMARY OF REPORTED PULMONARY ABSORPTION
RATES FOR BENZENE
Percent
Absorption
20.42a
20-50
28-34
45. 8,48. Oa
.46
47
53-63
63
Concentration
(ng/m3)
191-255
150-350
19140
*
166-198
320
112
80-100
b
Duration
of Exposure
4 hours
2-3 hours
4 hours
5 hours
5-7 ninutes
3-4 hours
>2 hours
Reference
Nomiyama and Noniyarns, 1969
Srbova et al., 1950
Duvoir et al.t 1946
Nomiyama and Nomiyania, 197Ab
Teisinger et al., 1952
Hunter, 1966
Hunter and Blair, 1972
Fiserova-Bergerova et al.f 1974
values for males and females, respectively.
Not specified.
25
-------
Nomiyama, 197AB). If this is the case, then at much lower atmo-
spheric concentrations,.such as those ordinarily encountered by the
general population, the degree of saturation achieved at an equilib-
rium state will be quite low (since metabolism and elimination of
must of the absorbed benzene is fairly rapid; See section 4.1.4) and
the absorption rate should never drop far below the initial value (60
to 80 percent based on studies of Srbova et al.. 1950; Fiserova-
Bergerova et al., 1974). Although the absorption rates given in
Table 4-1 do not show a clear dependence upon concentration, as would
be required to confirm this reasoning, a comparison of absorption
rates and concentrations utilized suggests that there were signifi-
cant differences in the methods utilized and/or considerable varia-
bility in individual physiological parameters of the test subjects.
Because of the uncertainty over pulmonary absorption kinetics in the
ambient exposure situation, two values, 80 and 45 percent, will be
used in subsequent calculations.
One study (Nomiyama and Nomiyama, 1969) revealed significant
differences in the absorption rates of males and females. It was
suggested that females would therefore be more susceptible to benzene
intoxication. However, a more recent study by the same authors
(Nomiyama and Noniyaraa, 1974b) failed to confirm the original re-
sults.
An individual's degree of physical activity nay be an important
mediating factor. Egle and Gochberg (1976) observed an inverse
26
-------
relationship between the degree of benzene uptake and the ventilatory
rate in dogs.
4.1.2 G as t ro int e s t i n a 1Absorption
Acute benzene poisoning due to ingestion of the compound is rel-
atively uncommon (Gosselin et al., 1976), therefore little or no re-
search has been undertaken to determine the rete of gastrointestinal
absorption. However, because benzene is raiseible with organic sol-
vents and fairly soluble in water (the solubility in water is 820
Hg/l) (NIOSH, 1974; Howard and Durkin, 1974), it can be estimated
that nearly 100 percent of a small quantity of ingested benzene would
be absorbed. This estimate is supported by the high initial pulmon-
ary absorption rate. The presence of food in the GI tract may inhib-
it complete benzene absorption, since the compound may bind with or
be otherwise sequestered within bulk food materials. However, 100
percent will be considered a reasonable value for GI absorption.
.4.1.3 Derma1 Absorp t ion
Dermal contact with benzene should not be appreciable under
ambient environmental conditions, although exposure may result from
occasional contact with gasoline and benzene-containing solvents.
Benzene may be slowly absorbed through the skin (Hanke et al., 1961),
although in one study, in which subjects arms were iraeersed in ben-
zene for 25 to 35 minutes, no evidence of dermal aboorption was ob-
tained (Conca and Haltagliati, 1955). Given the extent of deraal
27
-------
exposures to benzene for the general population, deraal absorption
can be considered insignificant.
4.2 Metaboilc Pathways
The proposed scheme of benzene metabolism in huoans (Figure 4-1)
has been inferred from in vivo studies with mice, rats and rabbits,
and in vitro studies with isolated tissues and tissue fractions from
these animals (Gibson, 1971; NIOSH, 1974; Howard and Durkin, 1974).
The metabolic end-products shown In Figure 4-1 have been identified
in the urine of benzene-exposed persons (Teislnger et al., 1952;
Hunter and Blair, 1972). The relative proportion of metabolic
products has been determined in laboratory animals (Rusch et al.,
1977) but similar data from humans are not available.
Oxidation of benzene to the arene oxide (benzene-1,2-oxide) is
thought to be the initial metabolic step although this has not been
conclusively demonstrated (Gibson, 1971). The arene oxide is then
converted to one of three liydroxylated benzene derivatives; phenol,
trans-benzenediol (trans-1,2-dlhydro-l,2-dlhydroxybenzcne) , or S-(l,
2-dihydro-2-hydroxyphenyl)glutathione. The latter Is converted to
phenylmercapturic acid. Phenol may be conjugated with sulfates,
glycine, and glucurcnides or converted to quinol dihydroquinone
(hydroquinone) and conjugated. trans-Benzenedlol is also excreted in
conjugated form. Catechol (pyrocatechol), formed froa both phenol
and trans-benzenediol, is transformed to either hydroxydihydroquinone
(hydroxyquinol) or trans, trans-muconic acid. Catechol and
28
-------
S-Glu-Cys-Gly
S-CH2-CH-COOH
NH-CO-CH,
% , t
S-(l,2-dihydro-2-hydroxyphenyl}glutathione
Phenylmercapturic Acid
Benzene Benzene-1,2-oxide
Excretion via
Lung
IH
OH
S-
OH
trans-Benzcned iol Catechol
(trana-l,2-dihydro-(Pyrocatechol)
1,2-d ihydroxybenzene
trans,trons-
Muconic Acid
Phenol
Excretion via
Urine
Kyd roxydIhydroquinone
(Hydroxyquinol)
Quinol Dihydroquinone
(Hydroquinone)
SOURCE: Adapted from Truhaut, 1968; Gibson, 1971; Howard and Durkin, 1974.
FIGURE 4-1
PROPOSED PATHWAYS OF HUMAN BENZENE METABOLISM
29
-------
hydroxyquinol are also eliminated as conjugates. Conjugated phenol
appears to be the primary metabolic end-product in humans (Hunter and
<
Blair, 1972).
Benzene metabolism takes place mainly in the liver (Gibson,
1971; Howard and Durkin, 1974) although it is not restricted to this
organ. Experiments with mice suggest that benzene is also metabo-
lized in bone marrow (Andrews et al., 1977).
4.3 Retention Characteristics
The presence of benzene in the body is, for the most part, high-
ly transient (Howard and Durkin, 1974; Srbova et al., 1950; Hunter
and Blair, 1972; Fiserova-Bergerova et al., 1974). Benzene is re-
tained for the longest period in those tissues which exchange the
compound most slowly with the blood, i.e., fat and bone marrow
(Fiserova-Bergerova et al., 1974; Hunter and Blair, 1972), although
the available evidence suggests that the compound is almost complete-
ly eliminated from these compartments within a few days after the
cessation of exposure (Fiserova-Bergerova et al., 1974; Howard and
Durkin, 1974). Parke and Williams (1953) found only 2.6 percent of a
benzene dose in rabbit fat after two days. Most of the remaining
tissues appear to freely equilibrate with the blood (Fiserova-
Bergerova et al., 197.4).
Andrews and coworkers (1977) obtained evidence suggesting that
benzene is metabolized within the bone marrow of the mouse. If human
30
-------
bone marrow also has the capacity to metabolize benzene, then benzene
lifetime within the marrow will be shorter than that dictated by ex-
change kinetics. However, metabolites thereby produced may be
responsible for some of the toxic consequences of benzene exposure.
4.4 Elimination Characteristics
The primary routes of elimination of benzene from the body are
excretion, as benzene, from the lung, and as phenolic compounds in
the urine. Srbova and coworkers (1950) determined that 30 to 50 per-
cent of the absorbed benzene is eliminated as benzene by the lungs.
Furthermore, the rate of elimination via this route was seen to de-
cline rapidly, obeying a logarithmic relationship (indicating thac
the rate of benzene removal from the blood is proportional to the
blood-benzene level). In 10 subjects, 16.4 to 41.6 percent of the
absorbed benzene was eliminated via the lungs in 5 to 7 hours.
Elimination via the kidney is the second main route of benzene
excretion, although in this case the major excretion products are
phenol and its congeners, produced in the liver and possibly also in
the bone marrow. Only 0.1 to 0.2 percent of the absorbed benzene
dose is eliminated as benzene in the urine.
Following relatively short exposures (several hours), up to 87.1
percent of the absorbed benzene has been found to be eliminated with-
in 50 hours cs phenol (free and conjugated) by the urinary route
(Hunter and Blair, 1972). As with pulmonary benzene excretion, the
31
-------
rate of phenol excretion in the urine is proportional to the absorbed
benzene dose (and therefore the level in the blood) (Hunter and
Blair, 1972).
32
-------
5.0 SOURCE CONTRIBUTIONS TO DAILY BENZENE UPTAKE IN HUMANS
To evaluate the potential health risks associated vith benzene
in drinking water, it is necessary to ascertain an individual's total
dose of benzene, froia all exposure sources, and to determine the rel-
ative magnitude of the benzene contribution from drinking water.
5.1 Approach
The method employed in this study to estimate the degree to
which each major environmental source of benzene exposure contributes
to an individual's total daily uptake is based on probable exposure
cocditions (i.e., ambient benzene levels) as veil as absorption rates
for each exposure route. The method consists of a fivestep process:
o Definition of ambient concentrations of benzene for the major
exposure source (i.e., air, food, and drinking water)
o Determination of daily benzene intake from each exposure
source according to the relationship
1i ° ci " (Benzene>£
where 1^ is the daily benzene intake from each source, C^
is the consumption per day of each source (i.e., air, food,
drinking water), and (Benzene)^ is the concentration of
benzene in each source i
o Calculation of the amount of benzene absorbed from each ex-
posure source:
Ui » Ii Aj
where U^ is benzene uptake for each exposure source i, Ij
is daily benzene intake from each source i, end A: is the
fraction of benzene absorbed for each particular exposure
route j (i.e., inhalation or ingescion)
33
-------
o Calculation of the total daily benzene uptake (Uc):
U
t
i Aj) -SU£
for all appropriate pairs of i and j
o Determination of percent (?£> of total daily uptake (Ut)
provided by each of the three exposure sources (i.e., source
contribution factors):
Pi
»t
5.2 Basic Assumptions
Several assumptions were made in defining the amount of each
source material consumed each day. Reference Kan (ICRP, 1975) values
are utilized for daily air and food consumption rates. Values for
daily consumption of drinking water are those suggested by NAS (1977)
as conservative estimates (see Table 5-1).
Pulmonary and gastrointestinal absorption rates utilized in
subsequent calculations are specified in Table 5-1. Two pulmonary
absorption rates have been used. The first, 80 percent, is the ap-
proximate initial rate in humans exposed to high atmospheric concen-
trations (see Section A. 1.1). The second pulmonary rate, 45 percent,
is the average steady-state value measured in the same studies. The
gastrointestinal absorption rate is a worst case estimate but is jus-
tified, to some extent, by a number of considerations (see Section
4.1.2).
5.3 Esticated Daily Benzene Uptake
The relative contribution from each exposure route (i.e., air
food, drinking water) to an individual's total daily benzene uptake
34
-------
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was determined by using the estimated average environmental benzene
occurrence levels and absorption rates in the calculation sequence
previously described. Several concentrations of benzene in drinking
water were selected to represent the range of empirically determined
values. The benzene concentrations are thought to be representative
of average and maximum urban values. The level in food is a crude
estimate (see Section 3.2). Table 5-2 provides the exposure values
used in subsequent calculations. Table 5-3 provides an example of
the actual calculation sequence employed. In Table 5-4, the source
contribution factors for air, food, and drinking water are indicated
for an average adult.
Based upon the assumed urban ambient exposure levels, air is the
predominant source of absorbed benzene, contributing over 65 percent
of the total daily uptake at even the highest drinking yater concen-
trations utilized. Assuming the benzene concentration in air is 50
fig/n^ (the estimated urban average) and the pulmonary absorption
rate is 80 percent, drinking water contributes 1.7 percent of the
daily uptake of benzene when the benzene concentration is 10 |ig/l,
0.1 percent at 1 pg/l, and well below 0.1 percent at 0.1 and 0.3
pg/1, the values presumed to represent average ambient conditions.
Using the low estimate of pulmonary benzene absorption (45 percent)
adds at most 1.7 percent to the source contribution factor for water.
At the estimated maximum ambient urban air-benzene level of 200
a-', greater than 88 percent of the total daily benzene uptake is
36
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contributed by this source at all drinking water levels utilized and
less than 1 percent is contributed by drinking water.
The distribution of benzene in the atmosphere is apparently
highly non-uniform. Because gasoline combustion is a major source of
benzene emissions, concentrations of benzene in air are presumed to
generally be higher in areas with high traffic density (urban areas)
than in areas with low traffic density (rural areas). This has not
yet been confirmed, as ambient benzene levels in rural areas have not
been reported. Atmospheric concentrations of benzene are also ex-
pected to vary on a regional basis, that is, levels will generally be
higher in areas near benzene production and by-product manufacturing
facilities (particularly the Gulf Coast and Middle Atlantic States)
than in other areas of the -country. Whether or not these same fac-
tors also affect drinking water benzene concentrations has not been
determined.
Smoking may be a major source of absorbed benzene. The results
of one study indicate that a person may inhale as much as 91.5 fig of
benzene per cigarette or 1830 fig/pack. The latter figure is higher
than the total daily benzene intake from air (at 50 pg/m^), food
and drinking water. The percentage of benzene absorbed from the
inhaled smoke has not been determined.
Benzene intake during use of gasoline as a solvent cleaner may
also be significant. A person exposed to a gasoline concentration of
lOOppm (3200 ng/m^ benzene) as a result of this practice would
-------
inhale about 3840 jig of benzene per hour*, and would absorb 1728 to
3072 ug/hour.
5.4 Identification of Critical Receptors
As mentioned in Section 4.0, there is some evidence to suggest
that females are more susceptible to benzene intoxication than males.
These results have been attributed to the female's higher percentage
of body fat. Koaiyama and Nomiyama (1969) reported that female sub-
jects absorbed benzene frca the lungs more than twice as efficiently
as males; however, this result was contradicted by a more recent
study (Komiyaaa and Nomiyama, 1974b). In another study by these
authors (Noraiyama and Xomiyama, 1974a), the.percentage of absorbed
benzene excreted by the respiratory route was three times higher .in
men than in vonen and, therefore, women excreted a greater proportion
as urinary metabolites. This is presumably supported by Hunter and
Blair's (1972) finding in men that as the proportion of body fat
increases, the proportion of benzene excreted as urinary phenol also
increases. These results say indicate an increased susceptibility in
women, since the toxic effects of benzene may be due, at least in
part, to one or core of the metabolic products (Andrews et al.t
1977).
*Assuuning a coxsusption rate of 1.2 ro^ air/hr during "light
activity" <1CRP, 1975).
41
-------
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