BENZENE

CAS number: 71-43-2

Synonyms: Benzol; Phenyl hydride

Molecular formula: C6H6

RECOMMENDED BEI®
Determinant Sampling Time BEI Notation
S-Phenylmercapturic acid in urine End of shift 25 µg/g creatinine B
t,t-Muconic acid in urine End of shift 500 µg/g creatinine B

Basis for the Biological Exposure Index polation of past studies. A meta-analysis of 250,000
(14)
petroleum workers indicated that they were not at
The BEI for both determinants is based on the an increased risk of multiple myeloma as a result of
®
TLV –TWA of 0.5 ppm, which itself is derived from exposure to benzene or other petroleum products.
the extensive review with 217 references made by
(1)
the Chemical Substances TLV Committee. The
Uses and Properties
TLV, which also includes a 2.5 ppm short-term expo-
sure limit (TLV–STEL) and a Skin notation, was Benzene is a colorless, highly flammable, non-
established from epidemiological studies of past polar liquid with an odor that is characteristic of
occupational exposure that, in the absence of reli- aromatic hydrocarbons. Benzene can be supplied as
able biological monitoring data, was based on air industrial grade, nitration grade, or refined. Benzene
sampling results. It should be recognized that there has a molecular weight of 78.11 and specific gravity
are considerable uncertainties in the extrapolation of of 0.8765 at 20°C. It has a melting point of 5.5°C, a
estimates of high exposures in the past to levels of boiling point of 80.1°C, and a vapor pressure of 95.2
risk that can be considered acceptable today. torr at 25°C. Conversion factors at 25°C and 760
3 3
Acute toxic effects of narcosis have been recog- torr: 1 ppm = 3.19 mg/m ; 1 mg/m = 0.31 ppm.
nized for many years; chronic effects, such as blood Solubility in water is poor (e.g., 1.8 mg/mL at 25°C),
dyscrasias, have been identified since the 1930s. A but it is miscible in all proportions with ethanol,
(2) (3)
definitive review made by Alice Hamilton in 1931 chloroform, diethyl ether, acetone, and fat and oils.
makes specific reference to the risk of lymphatic and At body temperature, the partition coefficients are
(15)
myeloid leukemia and provides a 125-item biblio- reported to be 7.8 for blood–gas, 425 for fat–
(15) (16)
graphy. In contrast, the 1993 U.S. Agency for Toxic gas, and 334 for adipose tissue–air.
Substances and Disease Registry toxicological pro-
(3)
file lists more than 800 references. While animal Absorption
studies have been helpful in establishing mechan-
isms, the key information was derived from re- Under most workplace exposure conditions,
evaluation of exposure data and medical records of benzene is absorbed by inhalation. Dermal absorp-
workers, particularly those employed in the manufac- tion from gaseous benzene probably contributes
ture of Pliofilm during a period stretching from the rather little to total absorption, but absorption from
(17)
1940s to the 1960s
(4–6)
and elsewhere.
(7,8)
Other liquid benzene can be significant. Gastrointestinal
(9) (10)
studies, principally in Italy, Turkey, and Chi- absorption is practically unknown in occupational
na,
(11,12)
have confirmed acute myelogenous leuke- exposure. The limited solubility in water and prefer-
mia as the most common malignant disease assoc- ential partition in the lipid phase leads to the bioac-
(18)
iated with chronic benzene exposure. Animal studies cumulation of benzene in fat and fatty tissues.
and occupational epidemiological studies have been Pulmonary
extensively reviewed in the TLV Documentation for
(1)
Benzene, and reference should be made to that Inhaled benzene is readily absorbed. The pul-
text for a detailed discussion and interpretation of monary retention stays at approximately 50% for
risk. A review of retrospective exposure assessment several hours at exposures between 2 and 100
(13) (19–22)
published in 1996, which summarized four studies ppm. Assuming a respiratory rate of 16 breaths
of benzene exposure in petroleum marketing and per minute and a tidal volume of 0.5 liter, approxi-
distribution, emphasized the uncertainties of extra- mately 7.5 µL benzene can be expected to be

2001 © ACGIH Benzene BEI – 1

 FIGURE 1. The major pathways of benzene metabolism. Chemical structures in brackets are postulated intermediates.

2 – Benzene BEI ACGIH  2001

absorbed each hour through the lungs of a person sure for 4 hours, triphasic elimination has been
(21)
inhaling air containing 10 ppm benzene. reported with rate constants of 3.66, 0.737, and
0.0158 for men and 3.02, 1.09, and 0.0429 for
Dermal (37)
women. For a single subject exposed for 1 or 8
(23)
Franz concluded from in vivo and in vitro tests hours, half-times of about 1, 4, and 25 hours have
(36)
on human and other skin that contact time was a also been reported, though the first may be better
major factor controlling percutaneous absorption of represented by two phases of about 20 minutes and
benzene. Under conditions where contact time was 2 hours. Elimination studies have recently been
(38)
short, less than 0.2% of the applied dose was reviewed.
absorbed (approximately 0.01 µL/cm ), due to its
2 The long-term retention and elimination of
volatility. Larger doses that persisted on the skin for benzene is influenced by both the concentration and
up to 3 hours resulted in 10 to 100 times greater duration of exposure. The amount of benzene
(17) absorbed and eliminated over 10 or more work
absorption. Blank and McAuliffe determined pene-
tration of benzene in a gasoline solution through hours appears to depend directly on the energy
(36)
human abdominal skin in vitro to be 1.4 × 10
–3 expenditure of the subject. Elimination may also
cm/hour, and the flux of benzene from air saturated be influenced by energy expenditure after work and
with benzene at 31°C to average 1.0 µL/cm /hour.
2 by circadian rhythms.
Based on studies of benzene absorption through the
(24)
skin of hairless mice, Susten et al. estimated that Metabolic Pathways
a worker dermally exposed 150 times per day to a and Biochemical Interactions
rubber solvent containing 0.5% benzene would
The metabolic pathway of benzene in humans is
absorb 4 to 8 mg. This compares to the estimated
shown in Figure 1. The metabolism is very complex
retention of 14 mg after 8-hour exposure at 1 ppm of
(25) and has not been fully elucidated. (See Snyder et
benzene in air. Fiserova-Bergerova reported skin (39) (40)
2 al. and Yardley-Jones et al. for reviews of the
penetration rates of 0.2 to 0.7 mg/cm /hour. Laitinen
(26) toxicity and metabolism of benzene.) Benzene is
et al. reported that the skin was the main route of
oxidized primarily in the liver by the cytochrome P-
absorption of benzene among garage workers
450-dependent monooxygenase to benzene oxide.
exposed to liquid gasoline.
Although several cytochrome P-450 isozymes may
Gastrointestinal catalyze this reaction, at low levels of exposure, the
ethanol-inducible isozyme IIE1 seems to be mainly
Gastrointestinal uptake of benzene has led to responsible.
(39)
acute intoxications, which suggests effective absorp- Benzene is primarily metabolized to phenol,
tion. Animal experiments confirmed that gastrointes- hydroquinone, and catechol. Hydroquinone and
(27)
tinal absorption was essentially complete. catechol are further metabolized to 1,4-benzo-
quinone and 1,2,4-trihydroxybenzene, respectively.
Elimination Benzene is also metabolized to the ring-opened
Metabolism is the main elimination pathway. oxidation product t,t-MA via the corresponding
Approximately one-third of retained benzene was aldehyde inter-mediate. Initial oxidation of benzene
occurs via two concurrent pathways involving either
excreted rapidly in urine as conjugated phenol and
(28–31) direct hydroxylation or formation of an epoxide
dihydroxy-phenols. The remainder was further
(benzene oxide). Enzymatic hydrolysis of benzene
degraded to become incorporated in tissue or
(32) oxide yields phenol and benzene glycol, the latter of
exhaled as carbon dioxide (CO2). Benzene was which dehydrogenates to catechol. Benzene oxide
mainly excreted in the urine as metabolites, notably also forms an addition product with glutathione,
as the conjugates of phenol with glucuronic and which is a precursor to phenylmercapturic acid.
sulfuric acids, and in exhaled air, as the unchanged The majority of these metabolites are excreted
form. Workers occupationally exposed at 100 ppm in urine as glucuronide and sulfate conjugates of
benzene excreted in urine the following proportions phenol are the primary urinary metabolites of ben-
of their absorbed does: 13.2% as phenol; 1.9% as zene. Others include conjugates of catechols and
quinol; 1.6% as t,t-muconic acid (t,t-MA); and 0.5% quinol, mercapturic acids, t,t-MA, and the reaction
(33)
each of catechol and 1,3,4-benezentriol. Small product of benzene with guanine, N-7-phenylgua-
amounts of unmetabolized benzene have also been nine.
(34,35)
detected in the urine. The proportion of Benzene metabolism to phenol, formation of
absorbed benzene excreted via exhalation was water-soluble phenyl glucuronide and sulfate conju-
(20,22,28,36)
reported as 8% to 39%. gates, conjugation with glutathione, and urinary elim-
The elimination of benzene following typical ination of benzene as the S-phenylmercapturic acid
levels of occupational exposure follows first order (S-PMA) are considered detoxication pathways. The
kinetics with several consecutive half-times corres- presence of other hydrocarbons at concentrations
ponding to the disposition of benzene in different about the TLV did not appear to influence the uptake
(36)
body compartments. Following experimental expo- or metabolism of benzene at about 10 ppm.

2001 © ACGIH Benzene BEI – 3

 The TLV Documentation for benzene provides a The determination of benzene in blood provides
summary of benzene biotransformation and the a sensitive and specific method but is markedly
(1)
implication for human health risk assessment. affected by current or recent exposure. Due to the
initial short half-life of benzene in blood, samples
Possible Nonoccupational Exposure taken at the end of shift reflect only the most recent
exposure. Samples taken before the following shift
Exposure to vehicle emissions and smoking are can provide a good measure of exposure during
the two major sources of benzene exposure in the that, and previous shifts, but greater sensitivity is
general population. The emissions result from evap- required for analysis.
oration from gasoline which commonly contains 1% Benzene in exhaled air reflects the concentra-
to 5% benzene, the amount according to country, tion of benzene in blood, and presents the same
(18) problem of interpretation in end-of-shift sampling.
and from the exhausts of automobile engines.
Benzene and other aromatic hydrocarbons are This method has the advantage of offering a non-
(40)
formed during the pyrolysis of tobacco. Side- invasive method, but sensitive methods of sampling
stream smoke (345–529 µg/cigarette) contained and analysis have yet to be standardized.
more benzene than the mainstream smoke (6–68 Sampling of benzene or metabolites in urine
µg/cigarette).
(41) offers the advantage of lower dependence on time
About 400 of 5000 materials and products tested but introduces additional variability due to fluctua-
by U.S. National Aeronautics and Space Adminis- tions in urinary excretion rate. Increased concentra-
tration are understood to emit benzene vapors in tions of benzene in postshift urine samples appear
(42)
amounts ranging from 0.1 to 140 µg/g. Paints, to be a sensitive indicator of benzene exposure in
adhesives, marking pens, rubber products, and the intended TLV range. However, the quantitative
tapes were identified as products that emit benzene interpretation of the measurement is ambiguous at
and may contribute to indoor air benzene present, and the methods require validating. Con-
concentrations. sequently, a specific BEI for benzene in urine could
Benzene is ubiquitous in the environment. not be determined due to insufficient data.
Median indoor benzene concentrations were 7 µg/m
3 The determination of phenol, catechol, quinol,
in 200 homes without a resident smoker and 10 and 1,2,4-benzene-triol is not specific and sensitive
enough for the low-exposure range. At present, it
µg/m in 300 homes in which one or more smokers
3
(43) seems that hemoglobin and albumin adducts are not
resided.
applicable for routine biological monitoring because
The long-term average daily intake of benzene
of the sophisticated methods involved and their
by the general nonsmoking population in the United
limited sensitivity.
States has been estimated to be between 63 and 73
Recent methods developed using high-perfor-
µg/day (maximum 149–222 µg/day) using three in-
(44) mance liquid chromatography (HPLC) and gas
dependent methods. For the average smoker (20 chromatography–mass spectrometry (GC-MS) for
cigarettes/day), an additional exposure of about 600 the determination of t,t-MA and S-PMA in urine
to 800 µg/day can be calculated. This may be com- appear to present an alternative approach for biolog-
pared with a calculated absorption of about 50 mg/ ical monitoring of benzene exposure in a very low
day for a worker exposed at a TWA concentration of range. S-PMA in urine requires a more sophisticated
10 ppm or 2500 µg/day if exposed at 0.5 ppm. technique than t,t-MA.
At the TLV–TWA of 0.5 ppm, urinary S-PMA and
TLV–TWA t,t-MA can be recommended as sensitive indicators
The TLV–TWA for benzene of 0.5 ppm (1.6 of workplace exposure. Both determinants are pres-
3 3
mg/m ) and a TLV–STEL of 2.5 ppm (8 mg/m ), with ent in very low concentrations in urine samples col-
a Skin notation and an A1, Confirmed Human lected from occupationally unexposed persons.
Smokers show higher levels than nonsmokers, and
Carcinogen, notation, was adopted in 1997. The
this may affect the relationship between biological
TLV is based on the prevention of excess risk of
levels and degree of exposure close to the TLV
cancer (leukemia) in humans associated with occu- range.
pational benzene exposure. The recommended TLV BEIs are recommended for measurement of S-
considers all routes of occupational exposure to PMA and of t,t-MA in urine collected at the end of
benzene and is derived from relative risk calcula- daily exposure. The measurements are principally
tions of excess risk of human leukemia associated indicators of exposure during the last shift but may
with chronic occupational exposure to benzene. also be influenced by longer-term retention of ben-
zene in the body.
Summary
The evaluation of occupational exposure to
benzene with biomarkers is based on 1) the determi-
S-PHENYLMERCAPTURIC ACID
nation of the unchanged parent compound in blood, IN URINE
urine, and exhaled air and 2) the determination of
various benzene metabolites in urine. In this Documentation, the units in analytical

4 – Benzene BEI ACGIH  2001

methods for urine samples are always expressed in ± 0.29 µg/g creatinine in 38 nonsmokers and 3.61 ±
µg/L. Reports on samples from occupational expo- 0.57 µg/g creatinine in 14 smokers. S-PMA was
sure are quoted in units of µg/g creatinine. The latter present at detectable concentrations in the urine of
is used to reduce the effect of the variability of urin- all smokers and in 20 of the 38 nonsmokers.
ary flow rate, and in this document, the creatinine
concentration is taken to be 1 g/L. For purposes of Kinetics
conversion, 1 µg/L is assumed to be equal to 1 µg/g
creatinine. The proportion of benzene taken up by the lungs
excreted in urine as S-PMA was estimated to be
Analytical Methods between 0.05% and 0.29% (average 0.11%). The
percentage was calculated from S-PMA concentra-
For adequate sensitivity of S-PMA determination tions in samples collected at the beginning and the
(48,49)
in urine, sophisticated methodology is necessary. S- end of a shift during several consecutive days.
PMA excretion in urine of exposed and nonexposed A higher conversion of about 0.9% was found by
(47)
persons has been assessed using liquid chromato- Stommel et al. In most workers, S-PMA was
(45,46) (47–50)
graphic and GC-MS methods. excreted in a single phase, but in some workers, a
The HPLC method, described by Maestri et biphasic excretion was found, and the highest S-
(46)
al., appears to be highly sophisticated and has not PMA concentrations were detected in samples at the
been validated in other laboratories. The detection end of the shift.
limit is 0.5 µg/L, the recovery of S-PMA is 90%, and In some workers, the highest S-PMA concentra-
the coefficient of variation is 3.8%. tions were measured at the beginning of the next
Determination using GC-MS is preferred shift. This difference may be due to interindividual
because it is the more sensitive and specific of the differences in toxicokinetics or the exposure of skin
two methods. The detection limits are 1 to 5 µg/L to benzene in the second group of workers, which
urine using S-benzylmercapturic acid as an internal may have led to a slower absorption of benzene into
standard. The detection limit is dependent on matrix the body than through respiratory exposure. The
effects, conditions of the ion selection detector, and average urinary half-time of elimination was nine
(48)
experience of the operator. In a recent study from hours [standard deviation (SD) = 4.5 hours]. In some
the same working group, a deuterium labeled S- workers, a tentative second phase of elimination
(pentadeuterophenyl)-mercapturic acid internal was seen with half-time of 45 hours (SD = 4 hours).
standard was used. The use of this internal standard From the half-time exposure to benzene, some S-
(49)
allowed a detection limit of 1 µg/L. The coefficient PMA (16%–30%) may still be excreted in samples
(48)
of variation of replicate analyses was 2.5% and collected at the beginning of the next shift.
3.5% at a spiked concentration of 13.1 and 50.1
µg/L, respectively. Factors Affecting Interpretation
The GC-MS method recommended by the Work- of Measurements
ing Group for Analysis of Hazardous Substances in
Biological Materials of the German Commission of Analytical Procedure and Sampling
(50)
Health Hazards at the Workplace utilizes S-p-
Because the outcome of the chemical analysis
fluorophenylmercapturic acid as an internal stan-
depends on the analytical procedure, the selection
dard. It has a detection limit of 1 µg/L urine.
® of the method is critical. For S-PMA determination,
ACGIH recommends GC-MS methods.
GC-MS is required for adequate sensitivity, and the
detection limit should be about 1 µg/L urine. The
Sampling and Storage
elimination kinetics indicate that the timing of sample
The urine specimen should be collected at the collection is critical for quantitative evaluation of
end of shift in polyethylene bottles and acidified to exposure. Since S-PMA is not likely to be present in
pH 2 with hydrochloric acid. Stability studies of S- the workplace, special precautions are not neces-
PMA in urine have shown that concentrations did not sary to avoid contamination of the sample.
(48)
change for at least one month if stored at 4°C.
Exposure
Biological Levels The following factors can affect the biological
Without Occupational Exposure levels: dermal exposure, interindividual differences
in toxicokinetics (see Kinetics), and smoking.
With the HPLC technique, a mean of 9.4 ± 5.9 (49)
Boogaard and van Sittert suspected that the
µg/g creatinine for nonexposed smokers, and 1.5 ± formation of S-PMA may be influenced by co-
1.2 µg/g creatinine for nonexposed nonsmokers was exposure to other aromatic hydrocarbons.
(35,46)
reported. According to the study of van Sittert et
(48)
al., S-PMA concentrations in smoking and non- Justification
smoking control persons were mostly below the
detection limit of 1 to 5 µg/L urine. With the improved Relationships between external benzene expo-
(49)
GC-MS method, the mean S-PMA level was 1.99 sure and renal S-PMA excretion have been evalu-
2001 © ACGIH Benzene BEI – 5
 3
ated in field studies. Controlled laboratory and ìg/m (1 ppm) benzene, the average S-PMA
simulation studies are not available. Significant concentration in urine samples was 45 µg/g
correlations were observed for the relationship creatinine (90% CI = 20–95 µg/g creatinine). From
between benzene in air and S-PMA in postshift urine the extrapolation to the TLV–TWA of 0.5 ppm, there
(35,47–49,51)
specimens. would be a S-PMA level in urine of about 25 µg/g
(48)
Van Sittert et al. validated S-PMA as a bio- creatinine.
marker in 12 separate studies. The studies, on
workers who were potentially exposed to benzene Current Database Available
during manufacturing and maintenance operations in
chemical plants and refineries and in natural gas Sufficient data from four field studies are avail-
installations began in 1989. An 8-hour exposure at 1 able to support a BEI.
ppm benzene corresponds to 46 µg S-PMA/g
creatinine [95% confidence interval (CI) = 41–50 Recommendation
µg/g creatinine]. The authors estimated that with the ACGIH recommends monitoring S-PMA in urine,
sensitivity of their method, TWA exposure of 0.3 collected at end of shift, as a determinant of occupa-
ppm could be determined reliably. An airborne tional benzene exposure. The value of 25 µg/g (12
benzene exposure at the TLV–TWA of 0.5 ppm µmol/mol) creatinine is recommended as a BEI.
corresponds to a S-PMA excretion of 25 µg/g The test is specific, but inhalation of tobacco
creatinine. smoke will introduce elevated background values,
A similar study was performed by the same although these are likely to only reach the level
(49)
working group, including the determination of t,t- recommended for the BEI for very heavy smokers.
MA and S-PMA in urine. For the determination of S-
PMA in urine, a more reliable and sensitive method
was used. For the comparison of the method, 12 t,t-MUCONIC ACID IN URINE
studies at eight locations in four countries were
performed from 1992 to 1994 on workers who were Analytical Methods
potentially exposed to benzene during manufac-
turing and maintenance operations in natural gas Specific and sensitive HPLC methods have
production installations, refineries, and chemical been developed for determining t,t-MA in urine and
plants. Strong correlations were found between t,t- are preferred to gas chromatographic–mass spectro-
MA and S-PMA concentrations in samples from the metric (GC-MS) methods. The latter are more
end of shift and between either of these variables tedious as derivatization to trimethylsilyl esters is
and airborne benzene concentrations. Exposure at necessary.
an 8-hour TWA of 1 ppm benzene leads to a Analytical techniques for t,t-MA were only suit-
calculated average concentration of 47 µg S-PMA/g able in the past for measuring exposures to benzene
creatinine in samples from the end of shift. The in air greater than 1 ppm. Recent techniques are
(52)
value of 47 µg/g creatinine for S-PMA agrees well based on the work of Ducos et al., where methods
(53)
with the findings from the previous studies, where a have been compared by these workers and by
(54)
similar value was found. Therefore, the TLV–TWA of Ong et al.
(55)
0.5 ppm would correspond to a S-PMA excretion of Lauwerys et al. reported a sensitivity corres-
(49)
25 µg/g creatinine. This study confirmed the ponding to an 8-hour TWA of 0.5 ppm. The most
(56)
suitability of S-PMA to detect benzene exposures as sensitive method was probably that of Lee et al.,
low as 0.3 ppm. Due to its superior specificity and its who reported that concentrations as low as 25 µg/L
longer elimination half-life, S-PMA was considered could be detected, and a within-assay coefficient of
by the authors to be a more reliable and sensitive variation of < 7%. The more recent technique used
(57)
biomarker than t,t-MA in urine. by Ghittori et al., which employs a preloading
(51)
Popp et al. reported in a study on automobile column in the HPLC, and ultraviolet (UV) measure-
mechanics that the best correlation to benzene in air ment at 259 nm, is reported to have a detection limit
was found with S-PMA concentration in urine at the of 3 µg/L with an interassay coefficient of variation of
end of shift with a correlation coefficient of: 3.8% and a recovery of about 90%. To ensure
consistent results, strong anion exchange (SAX)
r = 0.81 [S-PMA-urine mg/g creatinine = 4.10
clean-up is essential, and the urine samples should
+ 10.98 benzene-air (mg/m3)].
be alkalized to pH 7–10. The paper by Bartczak et
(58)
Therefore, a TLV–TWA of 0.5 ppm should al. clearly demonstrates the enhanced sensitivity
correspond to S-PMA excretion of 22 µg/g of the new techniques.
creatinine. Other publications that describe analytical meth-
For a group of 145 workers exposed to benzene ods for t,t-MA include those by Boogard and van
(35) (49) (59)
in a chemicals plant, Ghittori et al. found a Sittert, and Inoue et al. A less-labor intensive
significant correlation between benzene in air and S- method using capillary electrophoresis has recently
PMA (µg/g creatinine) in postshift urine. From the been reported for discriminating urinary t,t-MA down
(60)
calculated regression at an 8-hour TWA of 3250 to 25 µg/L from nonsmokers and smokers.
6 – Benzene BEI ACGIH  2001
Sampling and Storage 1953, Parke and Williams recovered 1% to 1.8% of
(49) an oral dose in rabbits. These data are quoted by
Boogard and van Sittart report that samples (64)
Ducos and Gaudin, who provide a useful general
acidified to pH 2 with 6 M hydrochloric acid are sta- background to the t,t-MA determinant for benzene,
ble at least up to a month if stored at room tempera- (65)
as do Ong et al. The former conclude that their
ture or 4°C. Although t,t-MA was stable in urine sam- own studies
(52,53) (56)
and those by Lee demonstrate
ples stored at room temperature for up to one week that the percentage of inhaled benzene that is
without preservation, low concentration samples retained (assumed to be 50%) which is eliminated
kept at room temperature without a preservative lost as t,t-MA is 2.0%, 1.5% and 1.4% respectively. t,t-
(56)
10% to 30% t,t-MA after two weeks. MA is considered to have a half-life comparable to
that of phenol ( 5.7 hours). The longer half-life for
Biological Levels phenol (about 24 hours) demonstrated by Sher-
Without Occupational Exposure (36)
wood and others may be masked by the natural
The principal source of t,t-MA in urine of nonoc- background of t,t-MA and the effect of smoking.
cupationally exposed persons is benzene in tobacco These percentages are reasonably consistent with
(49)
smoke. Sorbitol, which is present in some foods, the report of Boogard and van Sittert that, on
may also elevate background values of t,t-MA.
(52,61) average, 3.9% (range 1.9%–7.3%) of an occupa-
(56)
For 23 nonsmokers, Lee et al. reported a tionally inhaled dose was excreted as t,t-MA with an
(49)
mean value of 0.13 mg/L t,t-MA (range, 0.03–0.33) apparent half-life of 5.0 (SD = 2.3) hours. They
and 0.14 mg/g creatinine (range, 0.01–0.29). For 35 show that some elevation of urinary t,t-MA was still
smokers, corresponding values were 0.25 mg/L evident 16 hours after exposure.
(0.03–0.77) and 0.19 mg/g creatinine (0.06–0.43).
Geometric mean values have been reported by Lau- Factors Affecting Interpretation
(55)
werys et al. as 0.13 mg/g creatinine for smokers of Measurements
not exposed to benzene, and as 0.06 mg/g creati-
(59)
nine for nonsmokers. Inoue et al. reported a Analytical Procedure and Sampling
97.5% value of 1.4 mg/L in unexposed persons, but Because the outcome of the chemical analysis
the sensitivity of the method they used did not permit depends on the analytical procedure, the selection
detection of t,t-MA in 64% of the men and women of the method is critical. For t,t-MA determination,
(57)
tested. Ghittori et al. reported similar values of only the most recently reported methods should be
0.207 and 0.067 mg/g creatinine, and 95th used. Urine samples must be alkalized at the start of
percentiles of 0.56 and 0.30 mg/g creatinine. the analytical procedure to ensure reproducible
(62)
Melikian et al. showed that mean levels of t,t-MA recoveries greater than 95% from all ion-exchange
in groups of male, female, and pregnant smokers columns.
were 3.6, 4.8, and 4.5 times those of nonsmoking The elimination kinetics indicate that the timing
(62)
counterparts. Ruppert et al. reported a median of sample collection is particularly critical for quanti-
background concentration of 0.13 mg/g creatinine tative evaluation of exposure. Samples should be
t,t-MA in 32 smokers and 0.065 mg/g creatinine in collected within one hour of the end of a shift. If
82 nonsmokers. In eight nonsmokers, they reported expo-sure is known to occur early in the shift,
an increase in t,t-MA excretion from 0.08 to 0.88 samples should be taken at a mid-shift break. Since
mg/24h from a dietary supplement of 500 mg sorbic t,t-MA is not likely to be present in the workplace,
(61)
acid. From this, Rupport et al. deduced that a special precautions are not necessary to avoid
typical dietary intake of 6 to 30 mg/day of sorbic acid contamination of the sample.
accounts for 10% to 50% of background t,t-MA in
nonsmokers, and 5% to 25% in smokers. Exposure
Further studies on levels from smokers are re-
The following factors can affect biological levels
ported under Field Studies in the “Justification” sec-
of t,t-MA: dermal exposure, interindividual differ-
tion below. The significant absorption of benzene
ences in toxicokinetics (see Kinetics), smoking,
from inhalation of tobacco smoke limits the sensitive- (61)
ity of monitoring for occupational exposure. A de- pregnancy, and absorption of sorbitol.
(59)
tailed study of benzene-related compounds in the Inoue et al. suggest that the level of elimina-
urine of cigarette smokers has been reported by tion may be suppressed by the concomitant absorp-
Ong et al.
(63) tion of toluene. The ability to convert benzene into
t,t-MA may be genetically determined and varies
(66) (67)
Kinetics significantly. Gobba et al. compared concentra-
tions of muconic acid in urine with those of benzene
The biological formation of muconic acid from in urine (as a surrogate of benzene exposure)
benzene was first demonstrated by Jaffe in 1909. In among bus drivers, and concluded that they could
1924, Thierfelder and Klenk determined that 3.7% of be grouped as poor muconic metabolizers and effi-
benzene injected as an intraperitoneal dose in rab- cient metabolizers, with mean values for muconic
bits was eliminated in urine as muconic acid. In acid of 108 and 916 µg/g creatinine, respectively.
2001 © ACGIH Benzene BEI – 7
TABLE 1. Database of Field Studies of t,t-Muconic Acid as a Benzene Exposure Determinant
Index for 0.5
Sex and Number ppm in air
Date Ref. # of Workers RegressionA (µg/g creat.)
1989 59 All: 365B MA (mg/g cr) = 0.989 benzene (ppm) + 4.429 4900
(r = 0.8270)
Male: 177B MA (mg/g cr) = 1.223 benzene (ppm) + 2.123 2700
(r = 0860)
Female: 188B MA (mg/g cr) = 0.939 benzene (ppm) + 5.396 5900
(r = 0.814)
1992 53 23 log MA (mg/L) = 0.891 log benzene (ppm) + 0.041 (610 µg/L)
1993 56 19 MA (mg/g cr) = 0.8502 benzene (ppm) + 0.02 430
(r = 0.88)
1994 55 Male: 38 log MA (mg/g cr) = 0.86 log benzene (ppm) + 0.15 800
(r = 0.81)
1995 49 58 Benzene (mg/m3) = 2.38 MA (mg/g cr) – 0.900 1000
(r = 0.959)
1995 35 Male & Female: 145 For air concentrations in limited range 0.01 to 0.5 ppm:
log MA (mg/g cr) = 0.506 log benzene (ppm) – 0.213 430
(r = 0.56)
For all air concentrations measured (up to 20 ppm):
log MA (mg/g cr) = 0.429 log benzene (ppm) – 0.304 370
(r = 0.58)
1996 57 Male & Female: 171 log MA (mg/g cr) = 0.549 log benzene (ppm) – 0.18 450
(r = 0.614)
1995 65 64 log MA (mg/g cr) = 1.05 log benzene (ppm) + 0.20 770
(r = 0.89)
1996 69 Male: 131 log MA (µg/g cr) = 0.69 log benzene (ppb) + 0.09 760
(r = 0.53)
1997 68 Male: 410 (r = 0.58C) 390
3
1998 70 31 log MA (µg/g cr) = 0.4815 log benzene (mg/m ) + 2.2208 208
(r = 0.46)
A
MA = t,t-muconic acid; cr = creatinine.
B
Includes non-exposed subjects. Values for women are heavily influenced by exposures > 100 ppm.
C
Based on 151 workers who excreted t,t-muconic acid above the limit of detection.

Field data generally indicate a greater variation of HPLC to urine samples from 64 men and 88
in urinary t,t-MA concentrations than in S-PMA. women occupationally exposed to benzene and from
However, in a study of 410 workers exposed to 213 nonexposed controls. The latter were mostly
(68) below the detection limit of the analytical method.
benzene, Hotz showed a correlation coefficient of
0.58 between air concentration and urinary Correction of results from exposed workers for cre-
elimination of t,t-MA for the 151 urine samples atinine concentration or specific gravity of urine
above the limit of detection, and of 0.41 for S-PMA. made little difference to the correlation coefficients.
The following correlations were reported for exposed
Justification and nonexposed persons:
Men + Women:
Field Studies
t,t-MA (mg/g cr) = 0.989 benzene in air (ppm) + 4.429
Relationships between external benzene expo- (r = 0.827)
sure and renal t,t-MA excretion have been evaluated Men:
in numerous field studies. The principal data are
shown in Table 1. In most of these, comparison was t,t-MA (mg/g cr) = 1.223 benzene in air (ppm) + 2.123
also made with elimination of S-PMA. Significant (r = 0.860)
correlations were observed for the relationship Women:
between benzene in air and t,t-MA in post-shift urine
(35,49,51,53,55–57,59,65,68–70) t,t-MA (mg/g cr) = 0.939 benzene in air (ppm) + 5.396
specimens. Controlled
(r = 0.814)
laboratory and simulation studies are not available.
(59)
In 1989, Inoue et al. reported the application From these, the following urinary concentrations
8 – Benzene BEI ACGIH  2001
of t,t-MA, corresponding to 0.5 ppm benzene in air shift concentrations were twice those in preshift
(8-hour TWA), are deduced: 4.9 mg/g creatinine for samples. The data presented did not permit estima-
men+women; 2.7 mg/g creatinine for men alone; tion of t,t-MA concentration after exposure to a ben-
and 5.9 mg/g creatinine for women alone. These zene concentration of 0.5 ppm (8-hour TWA). At the
calculated values may not be valid at concentrations mean value for benzene concentration in air of 2.6
3
around 0.5 ppm, as the exposure concentrations mg/m (0.8 ppm), the mean urinary excretion of t,t-
measured were generally much higher (up to 200 MA was 1.28 mg/g creatinine at the end of the shift,
ppm). A significant difference between men and which suggests a value of about 0.8 mg/g creatinine
women was reported. after an 8-hour TWA benzene exposure at 0.5 ppm.
(53)
In 1992, Ducos et al. reported that sampling The authors conclude that t,t-MA is suitable for rou-
results from 23 workers demonstrated a linear cor- tine biological monitoring, at least on a group basis.
(49)
relation between benzene exposure and urinary Boogaard and van Sittert. summarized 12
concentration of t,t-MA and that at a TLV–TWA of studies of urinary t,t-MA in 188 workers with mea-
0.5 ppm the concentration in urine is 0.61 mg/L. sured exposure to benzene vapor, and 52 control
Only 16% of air samples were below 1 ppm workers with no exposure. The regression equation
(53)
benzene. Unlike subsequent publications, they for the highly significant correlation obtained for 58
reported no improvement of correlation coefficients workers exposed for about 8 hours was:
after correction for creatinine concentration. The
(64) Benzene in air (mg/m3) =
1995 review by this group includes an analysis of
2.38 t,t-MA (mg/g creatinine) – 0.900
results obtained by other workers.
(56)
Lee et al. determined urinary t,t-MA in 19 (r = 0.959)
refinery workers exposed to benzene in the range From this, the t,t-MA concentration in urine
0.01 to 0.63 ppm. From linear correlation of the corresponding to the TLV–TWA of 0.5 ppm is 1.0
difference between t,t-MA concentration before and mg/g creatinine. No separate regression was given
after shift and benzene exposure, they determined for exposures in a limited range about the TLV; the
the following relationship: statistical analysis was on exposure concentrations
3
t,t-MA (mg/g creatinine) = up to 80 mg/m (25 ppm). The mean concentration
0.8502 benzene in air (ppm) + 0.02 was 0.037 mg/g creatinine among the unexposed
controls in 38 nonsmokers, and 0.058 mg/g creati-
(r = 0.614) (49)
nine in 14 smokers. The authors found it essential
From this, the urinary t,t-MA concentration following to alkalize urine samples to ensure reproducible
exposure at 0.5 ppm (8-hour TWA) can be calcu- recoveries from all ion-exchange columns > 95%.
(35)
lated as 0.43 mg/g creatinine. Urinary t,t-MA concen- In 1995, Ghittori et al. reported a significant
trations in non-exposed persons were determined to correlation between benzene exposure in air and t,t-
be 0.19 mg/g creatinine in 35 smokers and 0.14 MA (µg/g creatinine) in postshift urine of a group of
mg/g creatinine in 23 nonsmokers. 145 workers in a chemicals plant. For exposure
(55)
Lauwerys et al. reported a statistically signifi- concentrations in the limited range 0.01 to 0.5 ppm
cant correlation between air concentrations of ben- (geometric mean = 0.1 ppm, geometric standard
zene and t,t-MA in postshift urine of 38 male sub- deviation = 4.16) after logarithmic transformation,
jects employed in garages and coke ovens. After the linear regression was found to be:
logarithmic transformation, the linear regression was
log t,t-MA (mg/g creatinine) =
found to be:
0.506 log benzene in air (ppm) – 0.213
log t,t-MA (mg/g creatinine) (r = 0.56)
= 0.86 log benzene in air (ppm) + 0.15
Over the full range of air concentrations measured
(r = 0.81)
(< 20 ppm), the regression was:
The urinary concentration of t,t-MA corresponding to log t,t-MA (mg/g creatinine) =
a benzene exposure at 0.5 ppm (8-hour TWA) is 0.8 0.429 log benzene in air (ppm) – 0.304
mg/g creatinine.
(r = 0.58)
In 21 nonsmokers and 14 smokers not occupa-
tionally exposed to benzene, geometric mean values At the 8-hour TLV–TWA of 0.5 ppm benzene in
for t,t-MA in urine were 0.06 mg/g creatinine and air, the regressions predicted values for t,t-MA in
0.130 mg/g creatinine, respectively. The authors urine of 0.43 and 0.37 mg/g creatinine, respectively.
concluded that t,t-MA is a reliable indicator of ben- These may be compared with the reported back-
zene exposure even as low as 0.5 ppm. ground arithmetic mean values among those not
(51)
Popp et al. measured t,t-MA elimination in 26 occupationally exposed to benzene of 0.23 mg/g
car mechanics exposed to benzene up to a maxi- creatinine for 20 smokers and of 0.062 mg/g creati-
mum of 4 ppm. The authors reported significant cor- nine for nonsmokers. The authors also warn that the
relation between benzene exposure and concentra- ability to convert t,t-MA has been reported to vary
(66)
tion of t,t-MA in postshift urine (r = 0.54). The post- significantly and that this may complicate assess-

2001 © ACGIH Benzene BEI – 9

ment of benzene exposure. with a range of 0.2 to 0.6 mg/g. Very few false posi-
An extension of this study to 171 workers was tive results were found, and the method was found
(57)
published in 1996. The following linear correlation reliable even around the cut-off airborne exposure
was reported: level of 0.1 ppm. These authors also applied likely-
hood ratios to test the probability of exposure given
log t,t-MA (mg/g creatinine) =
a specific test result.
0.549 log benzene in air (ppm) – 0.18 (70)
Javelaud et al. reported a study of benzene-
(r = 0.614) exposed car mechanics and road tanker drivers, and
The t,t-MA concentration in urine corresponding to for the 31 drivers reported the regression
the TLV–TWA of 0.5 ppm is 0.45 mg/g creatinine. log t,t-MA (µg/g) =
This is in close accord with the earlier assessment.
2.2208 + 0.4815 log atmospheric benzene (mg/m3)
Fifty smokers not occupationally exposed to ben-
zene showed a geometric mean of 0.207 mg/g From this, a value of 208 µ/g t,t-MA for 0.5 ppm
creatinine, while 50 nonsmokers showed 0.067 mg/g benzene in air was deduced, which is considerably
(57) (70)
creatinine. Ghittori et al. further reported a 95% less than reported in other studies. The authors
upper limit of 0.563 mg/g creatinine for smokers and suggested that this could be explained by the
0.296 mg/g creatinine for nonsmokers. A value of differences in jobs or in the air sampling devices.
0.45 mg/g creatinine in urine appears to correspond
to over 50 cigarettes per day. Laboratory and Simulation Studies
(65,69)
Ong et al. undertook the most detailed Neither human laboratory studies nor simulation
studies of urinary t,t-MA in workers exposed to ben- studies specific to t,t-MA as a determinant for
zene, from which they concluded that t,t-MA was not benzene exposure have been reported.
specific for monitoring benzene exposures below
(63)
0.25 ppm. The first paper covered studies of nine Summary/Current Database Available
car mechanics and 13 pump attendants at filling
kiosks who were generally exposed below 1 ppm, Sufficient data from 11 field studies are available
and 42 nonsmoking workers in the shoe industry, to support a BEI.
whose exposure was generally above 1 ppm and
occasion-ally peaked at 100 ppm. The following Recommendation
linear regres-sion of logarithmic values was
ACGIH recommends monitoring of t,t-MA in
determined:
urine, collected at end of shift, as a determinant of
log t,t-MA (mg/g creatinine) = benzene exposure. The value of 500 µg/g creatinine
1.05 log benzene in air (ppm) + 0.20 is recommended as a BEI.
(r = 0.89) The test is specific, but inhalation of tobacco
smoke will raise background values, restricting
From this, the urinary t,t-MA concentration following monitoring to workers with benzene exposures
exposure to a benzene concentration of 0.5 ppm (8- greater than 0.25 ppm (8-hour TWA). Sorbitol, which
hour TWA) is calculated to be 0.77 mg/g creatinine. is present in some foods, may also elevate
(69)
The later paper reports samples from 131 non- (62)
background values, while concomitant exposure
smokers chosen from a larger group who were to toluene may depress t,t-MA concentrations.
(59)
randomly selected from petroleum refinery workers. The ability to convert benzene into t,t-MA is
The following linear regression was determined after genetically deter-mined, varies significantly between
logarithmic transformation of all results: (66)
individuals, and may depend on the efficiency of
(67)
log t,t-MA (µg/g creatinine) = t,t-MA metabolism.
0.69 log benzene in air (ppb) + 0.09
(r = 0.53) Other Reference Values
for those exposed to less than 0.25 ppm: r = 0.14 The German Commission for the Investigation of
for those exposed to more than 0.25 ppm: r = 0.55 Health Hazards of Chemical Compounds in the
(71)
Work Area treats benzene as a carcinogen and
From the regression, the urinary t,t-MA concentra- provides EKA values (exposure equivalents for
tion following exposure to a benzene concentration carcinogenic substances), rather than Biological
of 0.5 ppm (8 hour TWA) is calculated to be 0.76 Tolerance Values (BAT) values, for various degrees
mg/g creatinine. This paper also reported back- of inhalation exposure. The EKA values, as well as
ground values in non-exposed persons, but the the corresponding airborne level, appear in Table 2.
application of their conclusions is restricted to
nonsmoking workers. Other Indicators of Exposure
(68)
Hotz et al. compared S-PMA and t,t-MA acid
(54) (72)
in urine in 410 male workers, 95% of whom were Ong et al. and Schaller reviewed the
exposed to benzene below 0.5 ppm. Nonsmokers variety of monitoring indicators (e.g., blood, urine,
exposed at 0.5 ppm averaged 0.39 mg/g creatinine, and alveolar air) for the assessment of exposure to
10 – Benzene BEI ACGIH  2001
TABLE 2. German EKA Values for Benzene (71) ACGIH, Cincinnati, OH (2001).
2. Hamilton, A.; General Review: Benzene (Benzol)
Sampling Time: Poisoning. Arch. Path. Lab. Med. 11:434–454, 601–
End of Exposure or End of Shift 632 (1931).
Airborne Whole Urine 3. U.S. Agency for Toxic Substances and Disease
Concentration Blood Registry: Toxicological Profile for Benzene (Update).
of Benzene Benzene S-PMA t,t-MA TP-92/03. DHHS, PHS, ATSDR, Atlanta, GA (1993).
in ppm3 (µg/L) (mg/g cr)* (mg/L) 4. Kipen, H.M.; Cody, R.P.; Crump, K.S.; et al:
Hematologic Effects of Benzene: A Thirty-Five Year
0.3 0.9 0.010 — Longitudinal Study of Rubber Workers. Toxicol. Ind.
0.6 2.4 0.025 1.6 Health 4:411–430 (1988).
0.9 4.4 0.040 — 5. Hornung, R.W.; Ward, E.; Morris, J.A.; Rinsky, R.A.:
1.0 5.0 0.045 2 Letters to the Editor. Toxicol. Ind. Health 5:1153–1155
(1989).
2.0 14 0.090 3 6. Kipen, H.M.; Cody, R.P.; Goldstein, B.D.: Letters to the
4.0 38 0.180 5 Editor. Toxicol. Ind. Health 5:1156–1158 (1989).
6.0 — 0.270 7 7. Infante, P.F.; Rinsky, R.A.; Wagoner, J.K.; Young,
R.J.: Leukaemia in Benzene Workers. Lancet 2:76–78
*cr = creatinine
(1977).
8. Rinsky, R.A.; Smith, A.B.; Hornung, R.; et al.: Benzene
benzene. Table 3 provides an overview of other and Leukemia. An Epidemiologic Risk Assessment. N.
indicators currently available for biological Engl. J. Med. 316(17):1044–1050 (1987).
monitoring of benzene exposure. The advantages 9. Vigliani, E.C.: Leukemia Associated with Benzene
and disadvantages are listed for each parameter Exposure. Ann. N.Y. Acad. Sci. 271:143–151 (1976).
taking into particular consideration specificity, 10. Aksoy, M.: Benzene as a Leukemogenic and
sensitivity and practicability. Carcinogenic Agent. Am. J. Ind. Med. 8:9–20 (1985)
(34)
Ghittori et al. demonstrated that the 11. Yin, S.N.; Li, G.L.; Tain, F.D.; et al: A Retrospective
Cohort Study of Leukemia and Other Cancers in
determination of benzene in urine can provide a
Benzene Workers. Environ. Health Perspect. 82:207–
sensitive and specific indicator for the biological 213 (1989).
monitoring of occupationally exposed workers. Ong 12. Yin, S.A.: A Cohort Study of Cancer Among Benzene-
(65,69)
et al. reported that unmetabolized benzene in Exposed Workers in China: Overall Results. Presented
urine provided good correlation with ambient at the International Conference on the Toxicity,
benzene, but data were insufficient to confirm it as a Carcinogenicity and Epidemiology of Benzene.
useful biomarker of exposure, and serious technical Environmental Health Sciences Institute, Piscataway,
drawbacks limit its use. At present, the experience NJ (June 17–20, 1995).
with the benzene in urine parameter is quite limited, 13. Rushton, L.; Thar, W.E.: Retrospective Exposure
and the method requires validating. This determinant Assessment for Benzene: Issues, Methods and
has been applied, together with a simple but Recommendations from an International Workshop on
sensitive method of determining benzene in exhaled Petroleum Marketing and Distribution Worker Studies.
(73)
breath, by Nordlinder et al. to determine Occup. Hyg. 3:295–305 (1996).
14. Wong, O.; Raabe, G.K.: Multiple Myeloma and
occupational exposure to gasoline.
(65) Benzene Exposure in a Multinational Cohort of More
Ong et al. also reported from two field studies than 250,000 Petroleum Workers. Regul. Toxicol.
that urinary hydroquinone shows a good correlation Pharmacol. 26:188–199 (1997).
with benzene concentrations in the breathing zone, 15. Fiserova-Bergerova, V.: Gases and Their Solubility: A
even at concentrations below 1 ppm. This finding Review of Fundamentals. In: Modeling of Inhalation
was based on one study and requires validation. In a Exposure to Vapors: Uptake, Distribution, and
(69)
subsequent review, they reported that a study of Elimination, Vol.1, pp. 16, 21. V. Fiserova-Bergerova,
hydroquinone excretion showed good correlation Ed. CRC Press, Boca Raton, FL (1983).
with exposure but could not detect airborne 16. Pierce, C.H.; Dills, R.L.; Silvey, G.W.; Kalman, D.A.:
exposure below 0.25 ppm. Partition Coefficients between Human Blood or
Excretion of 1,2,4-benzenetriol in the urine of Adipose Tissue and Air for Aromatic Solvents. Scand.
workers exposed to benzene was investigated by J. Work Environ. Health 22:112–118 (1996).
(33) 17. Blank, I.H.; McAuliffe, D.J.: Penetration of Benzene
Inoue et al., using an HPLC method that required Through Human Skin. J. Invest. Dermatol. 85:522–526
more complex preliminary treatment than t,t-MA. The (1985).
detection limit was 0.5 mg/L, which corresponded to 18. International Programme on Chemical Safety:
an 8-hour TWA benzene exposure of about 2 ppm. Benzene. Environmental Health Criteria 150. World
Excretion was suppressed by concomitant exposure Health Organization, Geneva (1993).
to toluene. 19. Srbova, J.; Teisinger, J.; Skramovsky, S.: Absorption
and Elimination of Inhaled Benzene in Man. Arch. Ind.
References Hyg. Occup. Med. 2:1–8 (1950).
20. Nomiyama, K.; Nomiyama, H.: Respiratory Retention
1. American Conference of Governmental Industrial Uptake and Excretion of Organic Solvents in Man. Ing.
Hygienists: Benzene. In: Documentation of Threshold Arch. Arbeitsmed. 32:72–83 (1974).
Limit Values and Biological Exposure Indices, 7th ed. 21. Rusch, G.M.; Leong, B.K.; Laskin, S.: Benzene

2001 © ACGIH Benzene BEI – 11

TABLE 3. Indicators, Other than S-Phenylmercapturic and t,t-Muconic Acids, That Have Been Used or Tested
for Assessment of Benzene Exposure at the Workplace and in the Environment
Minimum
8-Hour
Exposure
Detected
Determinant Advantages Disadvantages Method (ppm)
Measurement of Benzene in Biological Samples
Benzene in exhaled Specific, sensitive, simple Limited practicability, not GC-MS <1
air widely used, influenced by a
number of parameters
Benzene in blood Specific, sensitive Invasive, influenced by GC-FID head- <1
sampling time space technique
Benzene in urine Specific, sensitive, Limited experience GC-FID head- <1
noninvasive; correlates well space
with exposure technique

Measurement of Benzene Metabolites in Urine

Phenol Well-established methods Insensitive, nonspecific HPLC, GC 5
Catechol and quinol Limited experience, insensitive GC-HPLC 10
1,2,4-Benzene-triol Specific to damage route, Limited experience and HPLC 10
low background level sensitivity
N-Acetyl-cysteine Sensitive Influenced by tobacco smoking, HPLC
and thiophenol limited experience,
sophisticated methodology
N-7-Phenyl-guanine Specific to damage route Insensitive, rat data only GC-MS 5
Hydroquinone Sensitive, correlates with Very limited experience HPLC 0.25
external exposure
Other Indicators
Hemoglobin & Specific to damage route Insensitive, sophisticated GC-MS
albumin adducts, and methodology, limited
N-phenylvaline practicability and experience
adducts
Chromosome Nonspecific, insensitive
aberrations in
lymphocytes

GC = gas chromatography; FID = flame ionization detector; HPLC = high-pressure liquid chromatography; MS = mass spectrometry

Metabolism. J. Toxicol. Environ. Health 2:23–36 (1985)

(1977). 25. Fiserova-Bergerova, V.: Relevance of Occupational
22. Pekari, K.; Vainiotalo, S.; Heikila, P.; et al.: Biological Skin Exposure. Ann. Occup. Hyg. 37:673–685 (1993).
Monitoring of Occupational Exposure to Low Levels of 26. Laitinen, J.; Kangas, J.; Pekari, K.; Liesivuori, J.: Short
Benzene. Scand. J. Work Environ. Health 18:317–322 Time Exposure to Benzene and Gasoline at Garages.
(1992). Chemosphere 28:197–205 (1994).
23. Franz, T.J.: Percutaneous Absorption of Benzene. In: 27. Sabourin, P.J.; Chen, B.T.; Lucier, G.; et al.: Effect of
Applied Toxicology of Petroleum Hydrocarbons, 14
Dose on the Absorption and Excretion of [ C]-
Advances in Modern Environmental Toxicology, Vol.
Benzene Administered Orally or by Inhalation in Rats
V1. H.N. MacFarland, C.E. Holdsworth, J.A.
and Mice. Toxicol. Appl. Pharmacol. 87:325–336
MacGregor, et al., Eds. Princeton Scientific Publishers,
Princeton NJ (1984). (1987).
24. Susten, A.S.; Dames, B.L.; Burg, J.R.; Niemeier, R.W.: 28. Teisinger, J.; Fiserova-Bergerova, V.; Kudrna, J.: The
Percutaneous Penetration of Benzene in Hairless Metabolism of Benzene in Man. Pracovni Lekarstvi
Mice: An Estimate of Dermal Absorption During Tire- 4:175–188 (in Czech) (1952).
Building Operations. Am. J. Ind. Med. 7:323–335 29. Teisinger, J.; Fiserova-Bergerova, V.: Valeur

12 – Benzene BEI ACGIH  2001

Historical BEIs
Date Action Determinant Sampling Time BEI Notation
1985 Proposed Total phenol in urine End of shift 50 mg/L †G
Benzene in exhaled air: Prior to next
mixed-exhaled shift 0.08 ppm
end-exhaled 0 12 ppm
1987 Adopted Total phenol in urine End of shift 50 mg/L B, Ns
Benzene in exhaled air: Prior to next
mixed-exhaled shift 0.08 ppm Cf
end-exhaled 0.12 ppm Cf
1996 Proposed S-Phenylmercapturic acid in urine End of shift 25 µg/g creatinine
1997 Adopted S-Phenylmercapturic acid in urine End of shift 25 µg/g creatinine B
1999 Proposed t,t Muconic acid in urine End of shift 500 µg/g creatinine B
2000 Adopted S-Phenylmercapturic acid in urine End of shift 25 µg/g creatinine B
t,t-Muconic acid in urine End of shift 500 µg/g creatinine B

Comparée de le Détermination des Sulfates et du NASA, Johnson Space Center, Houston, TX (1990-
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Profes. 16:221–232 (1965). Environ. Health Perspect. 82:165 (1989).
30. Hunter, C.G.; Blair, D.: Benzene: Pharmacokinetic 44. Hathemer-Fray, H.A.; Travis, C.C.; Land, M.L.:
Studies in Man. Ann. Occup. Hyg. 15:193–199 (1972). Benzene: Environmental Partitioning and Human
31. Sherwood, R.J.: Benzene: The Interpretation of Exposure. Environ. Res. 53:221 (1990).
Monitoring Results. Ann. Occup. Hyg. 15:409–421 45. Jongeneelen, F.J.; Dirven, H.A.A.M.; Leijdekkers,
(1972). C.M.; Henderson, P.T.: S-Phenyl-N-acetylcysteine in
32. Parke, D.V.; Williams, R.T.: The Metabolism of Urine of Rats and Workers after Exposure to Benzene.
14
Benzene Containing C-Benzene. Biochem. J. J. Anal. Toxicol. 11:110–114 (1987).
54:231–238 (1953). 46. Maestri, L.; Ghittori, S.; Grignani, E.; et al.:
33. Inoue, O.; Seiji, K.; Nakatsuka, H.; et al.: Excretion of Measurement in Humans of Benzene Metabolite
1,2,4-Benzenetriol in the Urine of Workers Exposed to Urinary S-Phenylmercapturic Acid (S-PMA) with HPLC
Benzene. Br. J. Ind. Med. 46:559–565 (1989). (Italian). Med. Lav. 84:55–65 (1993).
34. Ghittori, S.; Florentino, M.L.; Maestri, L.; et al.: Urinary 47. Stommel, P.; Muller, G.; Stucker, W.; et al.:
Excretion of Unmetabolized Benzene as an Indicator Determination of S-Phenylmercapturic Acid in the
of Benzene Exposure. J. Toxicol. Environ. Health Urine An Improvement in the Biological Monitoring of
38:233–243 (1993). Benzene Exposure. Carcinogenesis 10:279–282
35. Ghittori, S.; Maestri, L.; Florentino, M.L.; Imbriani, M.: (1989).
Evaluation of Occupational Exposure to Benzene by 48. van Sittert, N.J.; Boogaard, P.J.; Beulink, G.D.J.:
Urine Analysis. Int. Arch. Occup. Environ. Health Application of the Urinary S-Phenylmercapturic Acid
67:195–200 (1995). Test as a Biomarker for Low Levels of Exposure to
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