EPA 560/5-76-003
HEALTH EFFECTS OF BENZENE
A REVIEW
JUNE 1976
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Toxic Substances
Washington, D.C. 20460
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Committee on Toxicology
Bertram D. Dlnman, Chairman
Yves Alarle
Mary 0. Amdur
Joseph F. Borzelleca
John J. Burns, Jr.
Arthur B. DuBols
Seymour L. Friess
Harold C. Grlce
Harold M. Peck
Charles F. Relnhardt
Frank G. Standaert
Robert G. Tardlff
Jack A. Winetead (Staff Officer)
Ralph C. Wands, Director
Advisory Center on Toxicology
National Academy of Sciences-National Research Council
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HEALTH EFFECTS OF BENZENE: A REVIEW
SUMMARY
Acute exposure to benzene produces toxic effects on the central
nervous system; however, in order to evaluate the chronic effects, con-
sideration must be given to the myelotoxic and possible chromosome-damag-
ing and leukemogenic effects of benzene. The time required for expression
of chronic benzene toxicity indicates a vast difference in individual
sensitivity. Some workers have shown signs of benzene poisoning after
brief chronic exposures while others display resistance for long periods
of time. The myelotoxic effects of benzene poisoning have been documented
in the shoe and rotogravure industries in the United States, Turkey, Italy,
and France. Aplastic anemia associated with benzene exposure may well
represent the most significant hazard.
Benzene has long been suggested as a leukemogenic chemical based
on many individual cases of leukemia which have been linked to benzene.
Although essentially all these cases were subjected to mixed exposures,
benzene was the chemical common to all cases. The first extensive
epidemiological survey to demonstrate a correlation between leukemia and
benzene exposure was reported by Aksoy e_t al.^ in 1974. The study of
28,500 shoeworkers showed an annual incidence of leukemia of 13/100,000
compared to 6/100,000 in the general population. Thorpe's epidemiologic
study^1 on 38,000 petroleum workers who had potential exposures to benzene
failed to indicate an increased incidence of leukemia. In spite of the
inherent shortcomings of Thorpe's study, it does seem to indicate that
there is not an outstandingly high incidence of leukemia in the workers
studied. His negative data, in contrast to Aksoy's findings, may be due
to the inadequacy of the follow-up techniques, lack of sufficient exposure
to benzene due to good work conditions, relatively weak or no leukemogenic
activity of benzene, or the absence of some necessary cofactors.
Most cases of severe benzene intoxication have been reported in
workers exposed to rather high concentrations of benzene under somewhat
unhygienic working conditions. It is probable that all cases reported as
"leukemia associated with benzene exposure" have resulted from exposure
to rather high concentrations of benzene and other chemicals.
It has been suggested in the literature that "benzene-induced leu-
kemia" may occur only in individuals who are highly sensitive because of
genetic constitution or because of synergistic action of other chemical
or physical environmental agents. A co-leukemogenic role for benzene
would explain the failure to induce leukemia in benzene-exposed animals.
The state of the benzene literature makes it very difficult or im-
possible to reach a firm conclusion on the dose-response relationship in
chronic exposure of humans to benzene. The details of the extent of ex-
posures are either inadequate or absent. Even in cases where some con-
centrations of benzene are reported, the stated concentrations were based
on occasional measurements of short durations. The role of benzene
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metabolism In its toxicity and the significance of benzene-induced
chromosome aberrations are currently unclear. It appears that a metabolite
of benzene may be responsible for its myelotoxic effects.
Bases on available literature, it can be concluded that benzene may
be associated with leukemia; therefore, benzene must be considered as a
suspect leukemogen. More definitive data are required for an accurate as-
sessment of the myelotoxic, leukemogenic and chromosome-damaging effects
of benzene.
RECOMMENDED RESEARCH
The review of the benzene literature clearly indicates that more
definitive data are required to assess accurately the human health effects
of benzene. Some areas of research which would be expected to yield
scientific results helping to elucidate the mechanism of chronic benzene
effects are listed below:
1. Inhalation studies using multiple animal species to provide
a firm data base for dose-response relationship to myelotoxicity,
and to determine leukemogenic potential. Another approach
would be to expose leukemia-prone mice to benzene.
2. Studies to assess the co-leukemogenic potential of benzene. One
possible approach would be the use of a combination of benzene
and radiation exposures with'the necessary controls.
3. More detailed metabolic studies to determine the animal model
most representative of humans, and to study the metabolism of
benzene in bone marrow. Since most carcinogens bind covalently
to cellular nucleic acid in the target tissue, 14C- or %-labelled
benzene could be used to investigate this possibility in experi-
mental animals or human tissues in vitro.
4. Studies to provide substantiating data on concentration and
dose/effect relationships between the severity of hemopathy and
frequency and significance of chromosomal abnormalities.
5. Determination of end-points for early detection of reversible
and irreversible changes due to chronic benzene exposure includ-
ing the possibility that benzene exposure results in specific
qualitative and quantitative changes in blood elements.
6. Further epidemiologies1 studies are needed, both retrospective
and prospective, particularly among industrial workers exposed
to benzene and related solvents. The possibility that leukemo-
genesis involves mixed exposure (benzene plus another agent or
factor) should be stressed in the design of these studies.
iii
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INTRODUCTION
This report Is in response to EPA's request for compilation, sum-
marization, and evaluation of the existing toxicological and epidemiologi-
cal information relevant to public exposure to benzene. Particular em-
phasis will be devoted to the effects on hematopoietic organs and the
existing evidence relating benzene to leukemia.
12
Browning wrote an extensive review article on benzene toxicitv
which was published in 1965. A number of recent review articles8'9'53'60'65
have appeared, including the National Institute for Occupational Safety
and Health (NIOSH) criteria document, "Occupational Exposure to Benzene"65
and a similar German document, ."Benzene in the Work Environment."" These
review articles and selected research papers, especially recent ones, will
provide the resources for this report. In addition to the extensive
collection of benzene literature in the library of the Advisory Center
on Toxicology, Medline searches were utilized to survey the current lit-
erature on benzene.
Benzene was discovered by Faraday in 1825 and has become an important
industrial chemical. The development of the chemical industry, especially
in the field of plastics, has firmly established the necessity for large
quantities of benzene as the starting material for chemical synthesis.
Benzene is consumed by the U. S. chemical industry at the rate of 1.4 billion
gallons annually and is expected to increase when additional production
facilities become available. It has been estimated by NIOSH that approxi-
mately 2,000,000 workers in the United States have potential exposure to
benzene. Additional uses for benzene are continually being found such as
the possible use of benzene and other chemicals to replace lead compounds
as antiknock components in motor fuels. Public exposures such as the
presence of benzene in gasoline and the possibility of increased content
in gasoline causes increased concern for benzene as a significant environ-
mental pollutant.
GENERAL PROPERTIES AND USES
Benzene (CgHg) is the parent hydrocarbon of the aromatic group, the
resonant cyclic compounds containing only carbon and hydrogen. Commercial
benzene is sometimes called "benzol." At room temperature benzene is a
colorless, clear liquid with a density of 0.87 g/cm and boiling point of
80.4 C. It has a melting point of 5.4-5.5 C, a vapor pressure of 74.6 mm
at 20 C and a flash point of 12 C. Benzene is slightly soluble in water
and miscible with alcohol, chloroform, ether, carbon disulfide, acetone,
glacial acetic acid and carbon tetrachloride. The high volatility of
benzene at room temperature is a very useful characteristic, but also the
chief source of hazard to workers.
Benzene is produced chiefly from coal tar distillation; however, it
is also produced from petroleum by catalytic reforming of light naphthas
from which It is Isolated by distillation or solvent extraction. Indus-
trial uses of benzene have included the following: extraction and rectifi-
cation, preparation of benzene derivatives for the chemical and pharmaceu-
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tical industries, as a solvent in the rubber industry, in glue for the
footwear industry, the preparation and use of inks in the rotogravure
industry, as a thinner for paints, as a degreasing and cleaning agent,
and as an anti-knock fuel additive. The industrial processes involving
production of benzene and chemical synthesis usually take place in sealed
and protected systems. The uses of benzene as a solvent and cleaning
agent have been decreased significantly, usually by using less toxic
substitutes.
Benzene in Gasoline
Since a vast amount of literature continues to accumulate on the
chronic effects of benzene exposure, the benzene content and effect of
benzene exposure from gasoline have become the subject for numeroup
studies.
Parkinson has conducted an investigation of'working conditions at
typical filling stations and at some oil company bulk loading installations
in England. The benzene concentration in the atmosphere measured at
three sites under variable weather conditions ranged from 0.3-3.2 ppm for
gasoline containing benzene in concentrations ranging from 3.1 to 5.8%
(V/V). At bulk loading facilities with benzene enriched gasoline up to
337, (V/V), the results were 1.4-9.4 ppm. The results obtained in this
study led Parkinson to conclude that only trivial exposure to airborne
benzene vapor occurred when gasoline with normal benzene content up to
5% (V/V) was dispensed at typical filling stations.
CO
In 1972, Sherwood reported results from a petroleum loading in-
stallation in Italy. The benzene content was approximately 2.7% by weight
of normal petrol and 4.5% for premium petrol. Loaders were exposed to
mean concentrations of 1.6-2.5 ppm over a 5-hour period; however, the
weigher working between the tracks was exposed to a mean concentration of
20 ppm. At the end of the work day the phenol content of the urine for
the workers correlated well with the exposure. The following morning
the phenol was normal in the loaders' urine, but remained elevated for the
weigher.
Q
Berlin et al. have recently published a review concerned with the
likely consequence of an increase in the aromatic content of motor fuels.
Due to the limitations of the European refining industry and the require-
ment to reduce lead, they estimate that the aromatic content can be ex-
pected to increase to approximately 48-507», since it takes above a 2%
increase in the aromatic content to improve the octane rating by one unit.
Although the actual exhaust composition will depend on the .type
engine and combustion conditions, some generalizations can be made regard-
ing the effects of increased aromatic content of fuel on the exhaust
emissions. The total volume of hydrocarbon emission decreases slightly
and the photochemical reactivity increases slightly; however, this is
considered to be of only secondary importance in Sweden.^ Oxidants were
not increased. Although not conclusive, results indicate a trend toward
increased aerosol formation with increasing aromatic content. The total
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amount of aldehydes is decreased and the amount of potentially carcino-
genic compounds (polynuclear aromatic hydrocarbons, PNA) will increase
with an increased aromatic content, but this will be small when compared
to other variables that affect emission of PNA.
Runion^ has published a study on the benzene content of Gulf's
gasolines in both the liquid and vapor phases, demonstrating a straight-
line relationship between benzene volume percent levels in the two phases;
however, it was observed that the volume percent in the vapor phase is
less than one-half the volume percent in the liquid phase. The volume
percent benzene in the gasoline vapors increased during evaporation
of a typical gasoline, but would not be significant in most cases, as it
is estimated that gasoline available at the typical service station pump
has not evaporated more than 1%. Runion concluded that it would be
difficult to exceed the Threshold Limit Value (TLV) of 10 ppm for benzene '
from exposures to gasolines containing 5% or less benzene. In 1972, Swiss
authorities enacted legislation limiting the benzene in gasoline to a
maximum of 5% by volume.
ACUTE TOXICITY
Benzene exposure causes acute toxic effects on the central nervous
system. Exposure to massive concentrations, in the region of 2.57= by
volume in air, is rapidly fatal. The symptoms are those of central nervous
system depression which may be preceded by convulsion, and death usually
follows from cardiovascular collapse. Browning^ has reported that fatal
cases recorded have usually occurred when benzene was inhaled in closed
spaces such as tanks. Severe non-fatal cases exhibit similar symptoms,
but recover after a period of unconsciousness. Milder exposures show
euphoria followed by giddiness, headache, nausea, and staggering gait,
and unconsciousness if exposure continues.
The severity of the symptoms of acute benzene toxicity and the
possibility of fatal outcome depend primarily on the concentration and
duration of exposure, but it is clear from documented fatal cases that
marked variations exist in individual susceptibility. This is suggested
by the fact that rescuers of workmen lying unconscious in tanks have died
while the original victim survived. Some authorities have interpreted these
data as an implication of the adrenals in benzene poisoning; however, it
could be due to cardiac sensitization with resultant fatal arrhythmias.
The chief anatomical changes determined during post-mortem examinations
of cases of acute fatal benzene poisoning are the presence of petechial
hemorrhages and abnormal fluidity of the blood.
CHRONIC TOXICITY
Benzene Induced Blood Disorders
In the earliest reports of benzene toxicity , benzene was recognized
as a powerful leucotoxin, destroying white cells of the circulating blood,
and severely injuring the bone marrow. Based on clinical records and ex-
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perimental work, the features of chronic benzene poisoning appear to be
marked changes in the blood secondary to selective localization and
accumulation of the chemical in the hemopoietic tissue.53 in chronic
benzene poisoning, changes in other organs and tissues are secondary to
changes in blood parameters and usually depend on these changes.
The signs of chronic benzene poisoning can appear any time from a
few weeks to several years of exposure.53 Typical symptoms may be head-
ache, a slight dizziness, nausea, vertigo at the end of work day, stomach
pain, loss of appetite, or feeling cold. If intoxication is more severe,
the clinical signs are more pronounced, such as weakness, blurring of
vision and dyspnea on exertion. The mucous membranes and skin may appear
pale. There is evidence of a hemorrhaglc tendency which may consist of
petechia, easy bruising, epietaxis, bleeding from the gums or menorrhagia.
Under these conditions blood examination usually suggests the presence of
marrow hypoplasia. This disorder is accompanied by a decrease in red
blood cells in the peripheral blood with a parallel or slightly lesser
fall in the hemoglobin level, indicating that it is a normochromic or
mildly hyperchromic form of anemia. Macrocytosis may occur as is often
the case with hypoplastic anemia. Regeneration appears to be slight or
absent, the number of white cells is low, usually less than 4000 per mm^
and there is a decrease in neutrophils and a relative lymphocytesis. In
addition, there is a shift to the right in the differential count, the
platelets are reduced in number and their morphology is altered (aniso-
cytosis, staining defects, pyknosis of the chromomere). The hemoglobin
turnover is reduced; the serum bilirubin is low and the amount of urobilio-
gen reduced, if no concomitant hepatic lesions are present. Red cell
fragility remains normal but there is a rise in serum iron due to defective
utilization of this element. The possible mechanism of this effect will
be discussed later. The marrow usually shows a diminution of cells, in-
cluding absence of megakaryocytes, but sometimes the most immature forms
of red and white cells are present in large numbers. Relatively few are
intermediate or late normoblasts, myelocytes or metamyelocytes because of
the marked shift in maturation.
The available evidence does not indicate that the reported benzene-
induced blood dyscrasias differ in any way from similar dyscrasias which are
caused by other myelotoxic agents or for which the etiology is unknown.
The course of hypoplastic marrow effects associated with benzene
exposure may be progressive unless action is taken to remove the person
from the toxic agent and to administer appropriate treatment. 3 if this
is accomplished in time, complete recovery may follow, but the process is
slow and defects in the blood constituents may continue for several years,
particularly with the white cells. With repeated exposures to benzene,
recurrences may readily appear and be more severe than previously. The
condition may become irreversible with or without repeated exposure, and
may develop into a state of chronic progressive pancytopenia; or it may
develop into an acute or subacute disease such as acute pancytopenia or
leukemia.
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Chronic pancytopenia has been associated with intense and prolonged
exposure to benzene or as a result of special characteristics relating to
the individual". Without an exposure to benzene for two years, the ap-
pearance of the severe blood disorders is rare. The clinical picture is
similar to that previously described, but the pallor and the anemia are
more noticeable. The hemoglobin level may be as low as 20% and the red
cell c^unt may be 1 million per mm3 or less. The leukocyte count falls
to less than 1000 per mm3, the neutrophil polymorphs being as low as 1 to
2%, and the platelets are barely detectable. The bone marrow becomes al-
most acellular. Hemorrhages are widespread, occurring mainly from severe
thrombocytopenia, but occasionally from hypoprothrombinemla and hypofibrino-
genemla.
» 53
Acute pancytopenia has been associated with benzene exposure . The
onset may be abrupt, even in subjects whose blood picture has remained
satisfactory or at least not been severely impaired by benzene. There is
severe pyrexia with toxemia and a rapid and severe drop in the level of
all the circulating elements of the blood. Anemia is usually hyperchromic
and macrocytic and hemorrhages are severe and widespread in these cases.
Blood cultures may prove positive from streptococci and sometimes for
staphylococci or E.coll. The outcome is fatal and death occurs in a few
days or weeks; however, modern therapeutic methods may increase survival time
and bring about temporary remissions.
Aksoy et. al.*- conducted a study on 217 workers who had been exposed
to benzene in the workplace at concentrations ranging between 30-210 ppm
from 3 mo to 17 yr. When compared to 100 control subjects, 51% of the
workers, showed hematological abnormalities attributable to chronic benzene
exposure. Leukopenla was detected in 9.7% of the workers; thrombocytopenia
in 1.84%. Leukopenia associated with thrombocytopenia was found in 4.6%
and leukopenia as a part of pancytopenia in 2.76% of the cases. Thus
17.5% of the workers had a white cell count of less than 4000/mm. Hemo-
globin levels were less than 12 g/100 ml in 33% of the workers and in
32.7% -the packed cell volume was less than 40%. While a mild or moderate
hypocnromic or normochromic anemia was present in 33% of the workers, the
same result was found in 21% of the controls. Oral iron was given to
some of the anemic workers with a resulting disappearance of the anemia;
therefore, the presence of an iron-deficiency anemia simultaneously with
chronic benzene poisoning was a possibility.
i O
[Later Aksoy et al. examined blood changes in workers suffering from
pancytopenia associated with long-term exposure to benzene. The estimated
exposure level varied from 150-650 ppm for 4 months to 15 years. Clinical
features and hematological data for all patients were generally similar;
however, the bone marrow results were different. It was found that the
patients could be classified into four groups. In addition to pancytopenia
the following findings were exhibited: hypoplastic or acellular bone
marrow, hyperplastic bone marrow, normoblastic bone marrow, and large
erythroid precursors, possibly a preleukemia state. Clinical symptoms
included macrocytic anemia, mild reticulocytosis, hyperbilirubinemia,
erythroblastemia, and increase in quantitative osmotic fragility and
elevated lactate dehydrogenase levels. The fetal hemoglobin (HbF) content
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in 20 out of 24 patients was increased although the mean values in groups
with hypoplastic, hyperplastic and normoblastic bone marrow were essential-
ly identical. The hemoglobin A» (HbA2) level was normal for 21 of 24
pancytopenia patients. Two showed a slight decrease and one a definite
decrease. The mean age of the group with normoblastic bone marrow had
the lowest mean age. The illness was less severe and the outcome more fa-
vorable in this group; however, there was no significant decrease in du-
ration of exposure, suggesting that older patients were more severely
affected by chronic exposure to benzene.
oy
Lange et a_l. has investigated the itnmunoglobulin levels in the
sera of 35 workers occupationally exposed to a combination of benzene,
toluene and xylene at estimated concentrations of 0.11 - 0.158 mg/1,
.203 - .27 mg/1 and .224 - .326 mg/1, respectively. The levels of three
classes of immunoglobulins (IgG, IgA, and IgM) of these workers were com-
pared to those of a control group consisting of 42 healthy adults. The
IgG and IgA levels decreased significantly, while the IgM level increased.
These results were found regardless of the period of exposure to the sol-
vents. It is suggested that the fall in IgG may reflect a suppressive ac-
tion of benzene on immunoglobulin-producing cells, resulting in the
inhibition of DNA synthesis and thus giving rise to IgM level due to impaired
feedback control of IgM synthesis by the lower level of IgG. This study
is treated as only benzene exposure disregarding possible effects of
toluene and xylene.
Since 10 workers in the above study were found to harbor auto-
O Q •*
leukocyte agglutinins, Lange et al^. performed a leukoagglutination test
and a cytotoxic test with leukocytes on 76 workers occupationally exposed
to the three solvents (benzene, toluene and xylene) and results compared
to a control group. Only one case out of 41 controls exhibited the
presence of leukocyte agglutinins; the agglutinins reacted with auto-
leukocytes but failed to produce agglutination of leukocytes from "0"
Rh-negative donors. In contrast, 10 exposed workers out of 35 had leukocyte
agglutinins reacting with autoleukocytes from "0" Rh-negative blood donors.
None of the sera was positive in the Gorer and O'Gorman cytotoxic test.
Data from this study suggest the occurrence of allergic blood dyscrasia
in some people exposed to benzene and its homologues.
CQ
A further study conducted by Smolik et a_l. on workers exposed to
benzene, toluene and xylene showed that 62 of 79 exposed subjects had a
complement level lower than the mean value of the control group. The mean
value of the exposed group was statistically significantly lower than that
of the controls (p<0.01). The data of this study are consistent with the
previous reports and suggest the involvement of immunologic factors in the
mechanism of the effects chronic exposure to benzene, toluene and xylene.
Yakushevich in Russia°° reported the results of a study on the dyna-
mics of the leucocyte content in the blood of white rats exposed to benzene
(from 50-5000 mg/m3), and toluene (from 30-1000 mg/m3). Under conditions
of chronic inhalation, leukopenia developed under the influence of benzene
or toluene while leukocytosis occurred under the influence of xylene. The
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degree of leukopenia caused by benzene or toluene was a function of con-
centration and the duration of the inhalation exposure. The time of onset
of a significant change in the quantity of leukocytes increased as the
concentration of the chemical under study decreased. Blood cholinesterase
activity during chronic inhalation of benzene, toluene or xylene decreased
as a function of their concentration and the duration of exposure. The
decrease in activity of the enzyme occurred at later times as the concen-
tration of the chemical decreased.
Kissling and Speck have reported results on studies of the
mechanism of benzene-induced aplastic anemia. Rabbits receiving a sub-
cutaneous dose of 0.2 ml/kg/d of pure benzene demonstrated peripheral
pancytppenia within 6-12 weeks. A marked decrease of leukocyte, thrombo-
cyte and retlculocyte counts occurred within 3 weeks which was followed
by a drop of the erythrocyte count and hemoglobin concentration. A left
shift in erythropoiesis and myelopoiesis was observed in the bone marrow
two weeks after the beginning of benzene injections. Autoradiographic
studies on the bone marrow cells of rabbits with benzene-induced pancyto-
penia showed a marked interference with DMA and RNA synthesis. It was
suggested by Kissling and Speck that the pancytopenia which follows benzene
exposure may be due to disturbed DNA- and RNA-synthesis rather than a
failure of the hemopoietic stem cell.
Chromosomal Effects
AQ
In 1964 Pollini and Colombi reported lymphocyte chromosome damage
in patients with benzene-induced aplastic anemia. Abnormal karyotype and
deletion of chromosomal material were frequently encountered. This report
was soon followed by another study of Pollini e£ a_l. " which attempted to
relate chromosomal alterations to the severity of benzene-induced blood
dyscrasia. The karyotypes of marrow parenchyma cells and peripheral blood
lymphocytic cells were examined in 4 subjects with temporary or progressive
blood dyscrasias. The incidence of heteroploid chromosomal patterns ranged
around 70% in the blood and marrow of each subject; however, there was no
correlation to the degree of evolution of blood dyscrasia. Likewise the
dispersion of chromosome number in the cells examined failed to relate to
the severity of the condition. Reports on numerous studies2^'21,27,32,57,63
involving benzene-induced hemopathies have yielded similar changes.
Vigliani and Forni reported chromosomal aberrations of both the
stable, and unstable type. In general the chromosomal aberrations were
higher in peripheral blood lymphocytes of workers exposed to benzene than
in those of controls. This was true even in the absence of overt signs of
bone marrow damage. The stable type was found to persist several years
after recovery from benzene hemopathy. Toluene and xylene failed to cause
a significant increase in chromosomal aberrations. The hypothesis was
suggested that benzene might induce various types of chromosomal aberra-
tions and that leukemia may develop in cases when potentially leukemic
clone with selective advantage is produced as a toxic response to benzene
exposure.
Two of the more recent articles from the same clinic in Italy,
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Clinlca del Lavoro "Lulgt Devoto," Milan ' present the most systematic
studies that have been conducted. In the first, 34 workers in a rotogravure
plant and 34 matched controls were compared. Because of the large number
of benzene hemopathies, as previously reported in this and other industries,
the government banned the use of benzene in certain industries and im-
posed a Maximum Allowable Concentration (MAC) of 25 ppm in 1953. There-
fore, this study was complicated by the fact that only 10 workers were
exposed to benzene (at levels of 125-532 ppm measured only in April 1953),
all well above the MAC from employment to this date (from less than 1 yr
to 22 yrs). In 1953 benzene was replaced with toluene containing traces
of xylene. The concentration of toluene in various locations in the
plant ranged from 0-240 ppm from 1954-1956; during 1957-1967, the concen-
trations were 56-824 ppm. The remaining 24 workers were exposed to the1
toluene only. The matched controls were exposed to neither of the solvents.
The 10 subjects exposed to benzene (and toluene) exhibited 1.66% and 0.62%
Cu cells and C8 cells, respectively. Toluene exposed subjects had 0.80%
and 0.08% C^ and Cg cells, respectively, which is not significantly
different from the control subjects with 0.61 C cells and 0.09% Cs cells.
Each metaphase was classified as follows: A, apparently normal; B, with
chromatic aberrations; Cu, with unstable chromosome changes (fragments,
rings, or dicentric chromosomes); or Cs, with stable chromosome aberra-
tions (abnormal monocentric chromosomes due to deletions, translocations,
trisomies, inversions, etc.). In Cu cells the presence of a fragment was
considered as one break, the presence of a dicentric ring chromosome as
two breaks. The unstable and stable chromosomal aberrations were signi-
ficantly higher in the benzene group compared with controls (P<0.01) and
the toluene group (P<0.05). A slightly higher rate of cells with more
than 46 chromosomes, primarily due to a higher rate of polyploid cells,
was observed in the benzene group; however, the difference was not statis-
tically significant. No significant differences were found between chromo-
somal changes in the toluene group and the control group.
19
In the later study from Milan, 25 subjects, who had recovered from
benzene hemopathy (4 with bone marrow pathology and in 3 subjects who had
recovered from acute exposure), revealed significant increased ratios of
stable and unstable chromosome aberrations, which in most cases persisted
for several years after cessation of exposure and recovery. Abnormal
metaphases in subjects recovered from benzene hemopathy were 1.89% Cu and
1.22% Cs which compares with 0.49% Cu and 0.04% Cs for the controls. At
the time of these chromosome studies, the hematologic follow-up gave nor-
mal blood counts in most cases; a few subjects still had a moderate anemia
and one still showed anemia, leukopenia and moderate thrombocytopenia.
One woman was eight months pregnant when admitted to the clinic in 1968
with pancytopenia after occupational exposure to benzene. Although severe-
ly pancytopenic, the patient delivered an apparently normal boy. The
following year the patient had another pregnancy and delivered a normal
baby girl. A cytogenetic study performed on the peripheral blood of the
newborn boy did not indicate any chromosomal abnormalities.
A study by Tough e_t a±. has shown a correlation between age and
chromosomal aberrations as well as between benzene exposure and chromosome
aberrations. No, correlation was found between the number of Cu cells
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and the years of exposure to benzene in any of the groups studied.
This series of studies indicated no correlation between the per-
sistence of chromosomal changes and the degree of benzene poisoning. It
is significant to note that no quantitative data on total benzene exposure
were available on all of the above studies on chromosome aberration on
humans.1 All indications point to very high levels probably several hun-
dred ppm.
Koizumi et. a_l. has reported a decreased DNA synthesis by cultured
human leukocytes and by HeLa cells that was observed from 2.2 X 10 M
benzene. Chromosome aberrations consisting of breaks and gaps were ob-
served in cultured human leukocytes in dose levels of benzene of both
1.1 X 10"3 M and 2.2 X 10"3 M; however, the significance of this finding
for human exposures at low concentrations must be questioned.
Kissling and Speck3^ studied the chromosomal aberrations in rabbits
injected subcutaneously with a dose of 0.2 mg/kg/d of pure benzene. The
karyotype was normal in 15 of 16 test animals; however, the frequency of
mitoses with chromosomal aberrations was initially in the range of 5.9%;
but increased to 57.8% after an average of 18 weeks.
Dobrokhotov of Russia*-" has reported studies using rats exposed to
0.2 g/kg/d benzene, 0.8 g/kg/d toluene and a mixture of benzene and toluene
at doses of 0.2 and 0.8 g/kg/d respectively. Chromosomal aberrations
were similar at the above administered doses of benzene and toluene, thus
indicating benzene as a stronger mutagen. The combined action of benzene
and toluene on the white rat took the form of total summation of the
evoked genetic effect of the two chemicals given separately.
Pierre has reported interim results of a study attempting to
determine the value of chromosomal analysis in the diagnosis of preleukemia.
Cytogenetic abnormalities were found in the preleukemic phase of acute
leukemia at approximately the same frequency and type exhibited in the
acute leukemia. Pierre stated that the failure to demonstrate an abnormal
cell line would not exclude preleukemia as it may be evolving into a
leukemia not characterized by observable cytogenetic abnormalities.
Sandberg^S has determined that visible chromosomal aberrations do not
occur in half the cases of acute leukemia and in some cases of chronic
myelocytic leukemia and almost all cases of chronic lymphocytic leukemia.
BENZENE EXPOSURE AND LEUKEMIA
The review of the literature reveals numerous cases of leukemia
attributed to benzene exposure; however, in essentially all reported
cases, benzene was only one of the chemical agents to which the worker
was exposed. For example, in the shoe industry, benzene was a solvent in
glue and in the rotogravure industry, benzene was a solvent for ink. Yet
articles have titles such as "Acute leukemia due to chronic exposure to
benzene."^ This paper describes four cases of acute leukemia which de-
veloped in shoemakers using benzene-containing adhesives. It is important
-------
to emphasize that the following discussion relating to human exposure
to benzene actually involve mixed exposure to chemicals with benzene
being a common one.
In 1961 Cronkite13 made the following statements:
The heart of the problem in the induction of leukemia by indus-
trial hazards rest upon quantitation of the agent and the yield
of leukemia. Two agents used in industry have been correlated
with an increased incidence of leukemia in human beings. The
first, ionizing radiation, is unquestionably able to increase
the incidence of leukemia. The second agent, benzol, probably
can produce an increased incidence of leukemia, but the data are
not as good as for the former. First, the finger of suspicion
must be pointed at any agent which is able to produce an aplasia
of the bone marrow, assuming it will probably be able to produce
leukemia also. Second, there is no reason to doubt that any
agent which will produce a cancer elsewhere in the body will not
be able to produce leukemia if the offending agent is transported
to the hemopoietic tissues.
Benzene fits in the former category because it is well documented
that it produces aplasia of the bone marrow.
Current opinion of the leukemogenic potential of benzene can best
be summarized by the following investigators' quotations:
Benzene is the only chemical agent strongly suggested to be
leukemogenic on the basis of striking occupational clusters,
although recent suspicion has been directed to chloramphenicol.
Occupational exposure to benzene is generally accepted as incurring
a risk of leukemia, especially erythroleukemia, although the inci-
dence of leukemia is low compared with that of hypoplasia affecting
one or more of the hemopoietic-cell series.24
Although some authorities still have some doubts, the association
between benzene exposure and leukemia is widely accepted as an
established fact.2
Even now benzene is the only serious contender for the status of an
accepted leukemogen. There is little question that the cases of
leukemia--ma inly acute—have occurred more frequently in persons
with a history of heavy occupational exposure to benzene or its
congener toluol than among the general population. °
Since the association between benzene exposure and leukemia was
first suggested by Delore and Borgomano, sufficient cases have been
reported to provide evidence that benzene can give rise to this
disease.^
10
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A cause and effect relationship between benzene and leukemia have
been difficult to establish. Despite some negative reports, it now
seems fairly clear that chronic exposure to high concentrations of
benzene may lead to one of several types of leukemia, the most
prevalent of which is acute or subacute myeloblastic leukemia.*>°
The first case of leukemia linked to the action of benzene was des-
cribed by Delore and Borgomano15 in 1928. In 1939 Mallory et a_l.41 des-
cribed two cases of leukemia among the patients who had chronic benzene
exposures in the industries around Boston. One patient had been exposed
to benzene for 10 years, 4 years heavily (200 ppm) and the succeeding
6 years lightly, but had shown hematologic evidence of benzene intoxi-
cation from the beginning of his employment. ° In the later 3 months of
his life, the typical pattern of an acute myeloid leukemia developed.
The characteristic findings of leukemia were found at autopsy which in-
cluded diffused myeloid infiltration of the liver, spleen, and bone marrow.
The other case was a twelve-year old boy, a painter's son, who used his
father's paint shop to repaint toys, and using a paint remover known to
contain benzene to remove the preceding coat. He developed aplastic anemia
but sternal puncture and sternal biopsy revealed a typical leukemic re-
placement of the marrow with undifferentiated cells of the lymphoblastic
series. Prior to these two cases, 10 cases of leukemia in patients who
had been chronically exposed to benzene had been reported. *• The recently
published German document "Benzene in the Work Environment" summarizes
over 250 reported cases of leukemia developed in subjects who had been
chronically exposed to benzene. The proven cases of leukemia are broken
down into three groups: cases of chronic exposure without evidence of
acute exposures but without any statement of exposure concentration;
cases with only vague exposure data; and cases including a numerical
statement of exposure concentrations. This case summary can be interpreted
as being indicative of a correlation between chronic benzene exposure and
the occurrence of various types of leukemia. These cases have been com-
piled from individual reports and collective surveys; therefore, it is not
possible to estimate the unreported cases or to calculate the incidence of
benzene leukemias in the general population, because the total number of
persons exposed to benzene cannot be determined. It is also impossible to
establish a quantitative relationship between the concentration and dura-
tion of exposure and the development of leukemia, because the number of
cases with exposure data is too small. In addition, the reliability of
the reported benzene concentrations appears very doubtful at best. One
case of acute myeloid leukemia was attributed to benzene exposure of less
than 25 ppm for over 4 years; however, subsequent studies revealed that
prior to the quoted time this subject had been exposed to much higher
concentrations of benzene. The authors also suggested that benzene hemo-
pathies are apt to develop in combination with other chemical (or probably
physical) effects. This contention is supported by the vast diversity of
effects developed in individuals under identical exposure conditions.
DeGowin1^ reported a case involving a painter who had been exposed
to benzene for 13 yrs. He developed a hypocellular bone marrow and pan-
cytopenia, followed by a relatively normal bone marrow with variable leu-
kopenia, anemia, and thrombocytopenia. Then after 15 yrs a frankly leukemic
11
-------
marrow and pancytopenia were found. DeGowln stated, "It Is tempting to
relate the blood diseases, or disease, to benzene exposure."
25
In 1971, Girard et aU reported the results of a three-year
systematic study conducted in France. The investigation was conducted
to determine the exposure to benzene or toluene in 401 subjects with
malignant hemopathies and in 124 controls admitted for non-hematologic
diseases. The bases of the study were by precise interrogations, in-
quiries in the work environment, and collection and analysis of products
used. The results indicated a much higher frequency of past exposures
to benzene or toluene among subjects with aplastic anemia (20.8%),
chronic lymphocytic leukemia (14.7%) and acute leukemia (12.1%) than
among the control group (4%). These differences were determined to be
statistically significant. The use of the hydrocarbons occurred
occupationally in 31 cases and domestically in 15 cases. Girard et. al.^5
concluded that the action of benzene hydrocarbons in the genesis of
malignant hemopathies should not be underevaluated.
2
In 1972, Aksoy et al. reported four cases of acute leukemia
attributed to chronic exposure to benzene. All of these patients had
worked in areas which were unhygienic and the concentrations of benzene
in air were between 150 and 200 ppm. The occupation of these four
patients was shoe manufacturing, and two of the four had suffered from
aplastic anemia two and three years respectively, before the onset of
acute leukemia. The other two cases of leukemia developed during their
exposure to benzene. One developed leukemia without any preceding episode
of aplastic anemia and the other developed leukemia followed by a transient
episode of pancytopenia lasting approximately two months. However, dur-
ing the transient period of pancytopenia the bone marrow was suggestive
of leukemia which was considered a preleukemic stage. Three of the four
cases of leukemia were of the acute myeloblastic type, the most frequent
type attributed to chronic exposure to benzene.^ The clinical and
hematologic evaluations of the subjects with acute myeloblastic leukemia
due to benzene did not differ from those of patients with acute
leukemia not related to benzene exposure. The fourth patient developed
thrombocythemia in the second year after an episode of aplastic anemia.
At that time the bone marrow did not reveal signs of leukemia, but
acute monocytic leukemia developed later. This type of leukemia is
rare among patients who develop the disease from benzene exposure.
Aksoy et al. reported that from 1967 to 1973, 26 patients among
28,500 shoeworkers chronically exposed to benzene in Istanbul developed
leukemia or preleukemia. The most common diagnosis was acute myeloblastic
leukemia, which was seen in 14 of the 26 cases. The duration of benzene
exposure varied from 1-15 yrs with a mean of 9.7 yrs. The 26 cases of
acute leukemia or preleukemia observed during this 7-yr period were
among a group of 28,500 workers at risk, or an annual incidence of
13/100,000. This incidence was reported as statistically significantly
greater (p> 0.02) than the incidence of 6/100,000 in the general popula-
tion; however, the statistical methods were not described. A peak in-
cidence of leukemia, 19.7/100,000 occurred between 1971 and 1973 but
no additional possible leukemogenic factors could be detected to explain
the higher incidence.
12
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The above reported data provide further evidence for an etiologic role
for benzene in leukemia; however, the statistical significance, of these
data should be investigated.
In a recent review article on industrial carcinogens,18 Eckardt made
the following statements:
i
The accumulation in the literature of cases of leukemia following
benzene exposures leads to the inevitable conclusion that benzene
is a leukemogenic agent, particularly in cases that have previously
displayed a panmyelopathy. Although this had long been suspected,
the data reported in the literature was not sufficiently convincing
to establish the leukemogenic nature of benzene. However, the more
recent observations seem to establish this association beyond a
doubt. More recent observations of chromosome changes in workers
exposed to benzene lend further weight to the leukemogenic nature
of benzene.
Thorpe"1 conducted the largest epidemiologic survey to date, using
workers of eight affiliates of the Exxon Corporation to determine the in-
cidence of leukemia in persons potentially exposed to benzene. Five
methodological problems were recognized and discussed which include: low
incidence of leukemia in the general population; validity of the diagnosis
of leukemia; quantitative determinations of the extent of exposures; in-
adequate follow-up on annuitants; and incomplete occupational histories
on individuals with diagnosed leukemia. Despite the problems and the
necessity for making a number of assumptions, Thorpe concluded that the
occurrence of leukemia in a population of 38,000 petroleum workers exposed
to low levels of benzene for 10 yrs was not different from the general
population in the countries concerned.
After Thorpe's paper was published in the Journal of Occupational
Medicine, Brown11 wrote a letter to the editor, which was highly critical
of Thorpe's work. Brown concluded his letter with the following statement:
!
With case-finding techniques as apparently relaxed as those in the
Exxon study by Dr. Thorpe, one cannot help but doubt the accuracy
of the data presented.
In 1975 McMichael e_t a_l. reported results of an epidemiological
study into work-related health problems. The study on rubber industry
workers indicates an association between leukemia and jobs entailing ex-
posure to solvents. Xylene, toluene, trichloroethylene and various
aliphatic hydrocarbons are among the modern solvents used in the rubber
industry. It was determined that the risk of death from lymphatic
leukemia appears to be approximately two-fold for workers in the medium
or low solvent-exposure jobs (compared to unexposed workers). The data
suggest that the leukemogenic agent is a chemical still present, rather
than one that was eliminated prior to 1945. The increased incidence is
primarily for the lymphatic type as compared to either the hemocytoblastic
or myeloblastic types associated with gross benzene intoxication. Data
obtained in this study also suggest a possible association between solvent
13
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exposure in the rubber industry and lymphosarcoma, Hodgkin's disease and
myeloid leukemia.
Aksoy £t al. have reported six cases of Hodgkin's disease in
patients with a history of chronic benzene exposure from 1-28 yrs prior
to the onset of the disease. A possible etiological relationship between
Hodgkin's Disease and benzene is discussed.
Li et^ aj^. have conducted a survey to evaluate the cancer experience
of chemists. This study was made by examining the causes of death among
3,637 members of the American Chemical Society who died between 1948 and
1967. Malignant lymphomas were significantly increased in male chemists
in both the 20-64 year, and over age 64, groups. Leukemia and cancers of
the pancreas and intestines were moderately increased in incidence over
the controls (0.01
-------
injections twice weekly for 44 wks and once weekly for the last 10 wks
of treatment. After the first 4 wks, the dose was 0.2 ml of 30% benzene
in corn oil per injection. The benzene-treated mice and controls were
killed 104 wks after the first injection and no evidence of carcinogenic
activity was found in either group. Butylnitrosourea, used as a positive
control, induced leukemia, lymphomas, and/or intestinal neoplasms in
essentially all of the mice.
Since animal experiments do not support the view that benzene is
a leukemogen, Ward et_ al_. & suggested that benzene-induced leukemia in
man may be a fairly rare event occurring only in highly sensitive in-
dividuals, because of genetic constitution, or because of synergistic ac-
tion with other environmental agents. Another point suggested to explain
the difference between man and animal models was a difference in meta-
bolism of benzene.
43
Miller has conducted an epidemiologic study to determine persons
with exceptionally high risk of leukemia. He has identified 5 classes of
persons whose probability of developing leukemia within a relatively shortg
time is 1 in 100 or greater. The classes represent a surprising diversity
of cytogenetic findings; however, a common denominator for each high-risk
group is a distinctive genetic or chromosomal feature which may play a
role in leukemogenesis. These classes represent a diversity of cytogenetic
features, such as genetic identity in the case of identical twin of child
with leukemia, genetically-induced chromosomal fragility in Bloom's and
Fanconi's syndromes, chromosomal breaks due to radiation, and congenital
aneuploidy in Down's syndrome. The genetic feature .for each high-risk
group may play a role in leukemogenesis. Aksoy ejt aj^. ^ have published
a report in which acute leukemia has occurred following exposure to benzene
in two relatives, a man and his paternal uncle. It was suggested that the
two patients with acute leukemia in two generations may have been due to
some genetic factors triggered by the chronic exposure to benzene.
\ Potolsky and Creger, * in a recent review article relating radiation
and drug therapies and leukemia, have proposed four mechanisms for the
induction of leukemia, which are as follows: chromosome breakage; activa-
tion of a latent leukemogenic agent (virus?); immunosuppression; and
marrow aplasia. These postulated mechanisms are not mutually exclusive
and data on benzene clearly indicates that it induces at least three of
the effects; however, if must be emphasized that the discovery of the
actual mechanisms involved in the etiology of human leukemia awaits further
investigations.
RELATIONSHIP BETWEEN BENZENE METABOLISM AND TOXICITY
Because inhalation is the primary route of exposure to benzene,
Nomiyama and Nomiyama^S have investigated the uptake, excretion and -
respiratory retention of benzene in humans. Six volunteers were exposed
to 52-62 ppm benzene for 4 hrs. After 3 hrs exposure, the respiratory
retention reached a constant level of 30%. The respiratory uptake at this
point was determined to be 46.9% and excretion was 16.8%. Nomiyama and
15
-------
Nomiyama^ also studied the respiratory elimination of benzene from
humans. Respiratory elimination refers to the excretion after the
cessation of the exposure. They found that the concentration of benzene
in expired air of persons exposed to benzene decreased from 10 ppm to
O.b ppm in 17 hours after exposure. Significant amounts of benzene were
eliminated unchanged through the lungs. Hunter and Blair^S have found
that humans retain approximately 230 mg of benzene from exposure to
80-10Q ug/1 for 6 hrs. It was determined that the elimination via the
lungs is no more than 12% of the retained dose. This value is signifi-
cantly less than elimination losses found in animals which are normally
quoted in the range 50-70%. Phenol measurement (free plus combined) on
the urine of the human volunteers indicated that 50-87% of the retained
benzene was excreted as phenol. The highest concentration of phenol was
found in the urine within about 3 hrs from the termination of the exposure.
In addition to phenol, hydroquinone, catechol, hydroxyhydroquinone,
trans-transmuconic acid and L-phenylmercapturic acid are excreted in the
urine.™ The phenolic metabolites are found primarily as glucuronide
conjugates and ethereal sulfate which can be liberated by hydrolysis in
strong acid. The metabolic fate of ^C-phenol has been studied in 19
species including man. The major route of metabolism in all species was
conjugation which included both ethereal sulfate .and glucuronide conju-
gates, except for the pig and the cat. The cat excreted the total dose
as phenylsulfate (87%) and hydroquinone sulfate (13%) while the pig ex-
creted only phenylglucuronide.
o
The rate of benzene metabolism depends on the dose given and the
presence of compounds which either stimulate or inhibit benzene metabolism.
Pretreatment with phenobarbital has been reported to increase the rate of
metabolism in both the rat and mouse.
Snyder and Kocsis^ have also reviewed the in vitro studies on
benzene metabolism. Evidence taken from several sources collectively
indicate that benzene is hydroxylated by cytochrome P450 and the mixed
function oxidase. The mechanism of benzene hydroxylation has not been
determined; however, it has been suggested that the reactions probably
occur via an arene oxide intermediate. Benzene oxide has not been found
in liver microsomes, probably due to its extreme lability, but naphthalene
oxide has been found when naphthalene was incubated with microsomes. In
addition, the incubation of benzene oxide with microsomes yields the
metabolic products of benzene.
The review of Nomiyama et_ al. work noted that young rats displaying
a high rate of benzene metabolism in vitro were also more susceptible to
subcutaneous injections of benzene than older rats exhibiting slower
benzene metabolism. They also reported protection against benzene toxicity
by 3-amino-l,2,4-triazole, which inhibits benzene metabolism in liver
homogenates. It was thus concluded that a metabolic product of benzene
was responsible for its hemotoxic effects. Ikeda and Ohtsuji^O treated
rats with phenobarbital and found a 3- to 4-fold increase in aromatic
hydroxylase measure in vitro. In vivo studies with phenobarbital pre-
treated rats showed an enhanced excretion of phenol in the urine. This
16
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suggests increased benzene metabolism since phenol is the major metabolite
of benzene. When phenobarbital pretreated rats were exposed to benzene
vapors an increased tolerance to the leukopenic action of benzene was
observed. These data were interpreted to support the idea that benzene
itself is the actual toxic substance. Saito ejb aJL5^ reported that
benzene metabolism is increased in rat liver microsomes after treatment
of rats with benzene, but not by treatment with resorcinol or phenol;
however, treatment with hydroquinone, pyrogallol or pyrocatechol actually
decreased the in vitro metabolism of benzene.
Drew and Fouts1^ have shown that both phenobarbital and 3-methylcho-
lanthrene induced benzene hydroxylase in rat liver; however, only chlor-
promazine induced benzene hydroxylase in the lung, and this was only
minimal induction. The LC5Q for inhaled benzene and the LDjo for injected
benzene were not changed by pretreatment of rats with either phenobarbital,
3-raethylcholanthrene or chlorpromazine. It was emphasized that while the
induction of metabolizing systems may not alter acute toxicity, they may
play a more important role in chemical toxicity due to chronic exposures.
Lee ejt a_l. have used the erythrocyte Fe utilization method to
study the effect of benzene on erythropoiesis in mice. After benzene
administration in doses of 440 or 2200 mg/kg, bone marrow suppression was
first detected 24 hours post-treatment with maximum suppression after 48
hours and complete recovery noted after 72 hours. The evidence in this
study suggests that benzene inhibits the multiplication of the erythrocyte
precursor cells and does not affect the incorporation of iron into heme.
Snyder and Kocsis, in their review, reported some additional
results from their laboratory using the 59pe utilization method and
labeled benzene. They found that when mice were administered toluene, a
competitive inhibitor of benzene metabolism, the rate of benzene metabolism
was reduced, and the ^9pe uptake into erythrocytes increased, thus indicat-
ing that benzene toxicity was alleviated. When mice were pretreated with
phenobarbital to increase the mixed function oxidase activity, an increase
in benzene metabolism occurred with a concurrent decrease in ->9pe uptake.
The results of these studies support the view that a metabolic step is
important in causing benzene toxicity.
Mitchell^ has reported that phenol, catechol, and hydroquinone
administered to rats for 1 wk failed to induce aplastic anemia, although
the highest doses killed approximately 50% of the animals. It was postulated
that the active metabolite was neither phenol, catechol or hydroquinone as
previously thought.
The above studies suggest that benzene metabolism may be of con-
siderable importance in benzene toxicity; however, the evidence is not
definitive. A problem pointed out by Snyder and Kocsis^ is that the
studies conducted on the metabolism of benzene, whether jLn vivo or iri vitro,
have been conducted in the liver. Chronic benzene toxicity manifests
itself in the bone marrow, thus the active metabolite must either be trans-
ported from the liver to the bone marrow or the metabolite is produced in
in the bone marrow. Since it has been suggested that RNA and DNA synthesis
17
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nay Influence benzene toxlctty, benzene oxide is a highly reactive species
that would be an excellent candidate for disturbing DNA and RNA synthesis.
The reactivity of benzene oxide thus would preclude its transport from
the liver to the bone marrow. It would appear that studies on benzene
.netabolism in bone marrow would be best for elucidating of the mechanism
of benzene toxicity. This is emphasized by the statement of Snyder and
Kocsis:
In any event, a point has been reached in the study of benzene
toxicity where we must recognize that there can be no more direct
approach to studying the disease than to investigate it in the
organ where it occurs.
18
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REFERENCES
1. Aksoy, M., K. Dincol, T. Akgun, S. Erdem, and G. Dincol. 1971.
Haematological effects of chronic benzene poisoning in 217
workers. Brit.J.Ind.Med. 28:296-302
2. Aksoy, M., K. Dingol, S.Erdem, and G. Din9ol. 1972. Acute
leukemia due to chronic exposure to benzene. Am.J.Med.
52:160-166.
3. Aksoy,M., K.Dinjol, S.Erdem, T. Akgdn, and G. Dinjol. 1972.
Details of blood changes in 32 patients with pancytopenia
associated with long-term exposure to benzene. Brit.J.Ind.Med.
29:56-64.
4. Aksoy, M., S. Erdem, and G. Dincol. 1974. Leukemia in shoe-workers
exposed chronically to benzene. Blood 44:837-841.
5. Aksoy, M., S. Erdem, K. Dingol, T. Hepyuksel, and G. Dincol. 1974. °
Chronic exposure to benzene as a possible contributary etiologic
factor in Hodgkin's disease. Blut 28:293-298.
6. Aksoy, M., S. Erdem, G. Erdogan, and G. Dincol. 1974. Acute
leukaemia in two generations following chronic exposure to
benzene. Hum.Hered. 24:70-74.
7. American National Standards Institute, Inc. 1969. Acceptable
concentrations of benzene. Z37.4-1969. New York, ANSI.
8. Benzene in the Work Environment. Considerations Bearing on the
Question of Safe Concentrations of Benzene in the Work Environ-
ment (MAK-Wert). 1974. Communication of the Working Group
"Establishment of MAK-Werte" of the Senate Commission for the
Examination of Hazardous Industrial Materials, prepared in
cooperation with Drf Gertrud Buttner. Boppard, Germany, Harald
Boldt Verlag.
9. Berlin, M., J. Gage, and E. Johnson. 1974. Increased aromatics
in motor fuels: A review of the environmental and health effects.
Work Environ. Health 11:1-20.
10. Bowditch, M., and H.B. Elkins. 1939. Chronic exposure to benzene
(benzol). I. The industrial aspects. J.Ind.Hyg.Toxicol. 21:321-
330.
11. Brown, S.M. 1975. Leukemia and potential benzene exposure. J. Occup.
Med. 17:5-6.
12. Browning, E. 1965. Toxicity and Metabolism of Industrial Solvents
New York, Elsevier.
19
-------
13. Cronkite, E.P. 1961. Evidence for radiation and chemicals as
leukemogenic agents. Arch.Environ.Health 3:297-303. •
14. DeGovin, R.L. 1963. Benzene exposure and aplastic anemia followed
by leukemia 15 years later. J.Am.Med.Assoc. 185:748-751.
15. Delore, P., and Borgomano. 1928. Leucemie aigue au cours de
1'intoxication benzenique. Sur 1'origine toxique de certaines
leucemies aigues et leura relations avec les anemies graves.
J.Med.Lyon 9:227-233.
16. Dobrokhotov, V.B. The mutagenic influence of benzene and toluene
under experimental conditions. Gig.Sanit. 37(10):36-39 1972.
[Translated by Air Pollution Technical Information Center,
Environmental Protection Agency, Research Triangle Park, N.C.
Translation No. HS-138.]
17. Drew, R.T., and J.R. Fouts. 1974. The lack of effects of pre-
treatment with phenobarbital and chlorpromazine on the acute
toxicity of benzene in rats. Toxicol.Appl.Pharmacol.27:183-193.
18. Eckardt, R.E. 1973. Recent developments in industrial carcinogens.
J.Occup.Med. 15:904-907.
19. Forni, A.M., A. Cappellini, E. Pacifico, and E. C. Vigliani. 1971.
Chromosome changes and their evolution in subjects with past
exposure to benzene. Arch.Environ.Health 23:385-391.
20. Forni, A., and L. Moreo. 1967. Cytogenetic studies in a case of
benzene leukaemia. Eur.J.Cancer 3:251-255..
21. Forni, A., and L.Moreo. 1969. Chromosome studies in a case of
benzene-induced erythroleukaemia. Eur.J.Cancer 5:459-463.
I
22. Forni, A., E. Pacifico,- and A. Limonta. 1971 Chromosome studies
in workers exposed to benzene or toluene or both. Arch.Environ.
Health 22:373-378.
23. Fraumeni, J.F., Jr. 1969. Clinical epidemiology of leukemia.
Semin.Hematol.6-.250-260.
24. Galton, D.A.G., and A.S.E. Spiers. 1971. Progress in the
leukemias. Prog.Hematol. 7:343-405.
25. Girard, R., F. Tolot, and J. Bourret. 1971. Malignant haemopathies
and benzene poisoning. Med.Lav. 62:71-76.
26. Gunz, F., and A.G. Baikie. 1974. Leukemia, 3rd edition. New
York, Grune and Stratton.
20
-------
27. Hartwich, G., G. Schwanitz, and J. Becker. 1969. Chromosome
anomalies in a case of benzene leukaemia. Ger.Med. Monthly
14:449-450.
28. Hunter, F.T. 1939. Chronic exposure to benzene (benzol). II.
The clinical effects. J.Ind.Hyg.Toxicol. 21:331-354.
29. Hunter, C.G., and D. Blair. 1972. Benzene: Pharmacokinetic
studies in man. Ann. Occup.Hyg. 15:193-199.
30. 'ikeda, M., and H. Ohtsuji. 1971. Phenobarbital-induced protection
against toxicity of toluene and benzene in the rat. Toxicol.
Appl. Pharmacol. 20:30-43.
31. Ishimaru, T., H. Okada, T. Tomiyasu, T. Tsuchimoto, T. Hoshino,
and M. Ichimaru. 1971. Occupational factors in the epidemiology
of leukemia in Hiroshima and Nagasaki. Am.J.Epidemiol. 93:157-165.
32..Khan, H., and M.H. Khan. 1973. Cytogenetic studies following
chronic exposure to benzene. Arch.Toxikol. 31:39-49.
33. Kissling, M., and B.Speck. 1971. Chromosome aberrations in
experimental benzene intoxication. Helv.Med.Acta 36:59-66.
34. Kissling, M. and B. Speck. 1972. Further studies on experimental
benzene induced aplastic anemia. Blut 25:97-103.
35. Koizumi, A., Y. Dobashi, Y. Tachibana, K. Tsuda, and H. Katsunuma.
1974. Cytokinetic and cytogenetic changes in cultured human
leucocytes and HeLa cells induced by benzene. Ind.Health (Japan)
12:23-29.
36. Laerum, O.D. 1973. Reticulum cell neoplasms in normal and benzene
treated hairless mice. Acta Pathol.Microbiol.Scand.Sect.A 81:57-63.
• i
37. Lange, A., R. Smolik, W. Zatonski, and J. Szymanska. 1973. Serum
immunoglobulin levels in workers exposed to benzene, toluene and
xylene. Int. Arch. Arbeitsmed. 31:37-44.
38. Lange, A., R. Smolik, W. Zatonski, and H. Glazman. 1973. Leukocyte
agglutinins in workers exposed to benzene, toluene and xylene.
Int.Arch.Arbeitsmed. 31:45-50.
39. Lee, E.W., J.J. Kocsis, and R. Snyder. 1974. Acute effect of benzene
on 59Fe incorporation into circulating erythrocytes. Toxicol.Appl.
Pharmtcol. 27:431-436.
40. Li, F.P., J.F. Fraumeni, Jr., N. Mantel, and R. W. Miller. 1969.
Cancer mortality among chemists. J.Nat1.Cancer Inst. 43:1159-1164.
41. Mallory, T.B., E.A. Gall, and W.J. Brickley; 1939. Chronic exposure
to benzene (benzol). III. The pathologic results. J. Ind.Hyg.Toxi-
col. 21:355-393.
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42. McMichael, A.J., R. Spirtas, L.L. Kupper, and J.F. Gamble. 1975.
Solvent exposure and leukemia among rubber workers: An epidemiologlc
study. J.Occup.Med. 17:234-239.
43. Miller, R.W. 1967. Persons with exceptionally high risk of
leukemia. Cancer Res. 27:2420-2423.
44. Mitchell, J.R. 1972. Mechanism of benzene-induced aplastic anemia.
Fed.Proc.Fed.Am.Soc.Exp.Biol. 30:561Abs, tt2044.
45. Nomiyama, K., and H. Nomiyama. 1974. Respiratory retention, uptake
and excretion of organic solvents in man. Benzene, toluene,
n-hexane, trichloroethylene, acetone, ethyl acetate and .ethyl
alcohol. Int.Arch.Arbeitsmed. 32:75-83.
46. Nomiyama, K., and H. Nomiyama. 1974. Respiratory elimination
organic solvents in man. Benzene, toluene, n-hexane, trichloro-
ethylene, acetone, ethyl acetate and ethyl alcohol. Int.Arch.
Arbeitsmed. 32:85-91.
47. Parkinson, G.S. 1971. . Benzene in motor gasoline--an investigation
into possible health hazards in and around filling stations and
in normal transport operations. Ann. Occup.Hyg. 14:145-153.
48. Pierre, R.V. 1974. Preleukemic states. Semin.Hematol. 11:73-92.
49. Pollini, G., and R. Colombi. 1964. Lymphoctye chromosome damage
in benzene blood dyscrasia. Med.Lav.55 •:641-654.
50. Pollini, G., E. Strosselli, and R. Colombi. 1964. Relationship
between chromosomal alterations and severity of benzol blood
dyscrasia. Med.Lav. 55:735-751.
51. Potolsky, A., and W.P. Creger. 1973. Radiation and drug therapies,
and leukemia. Annu.Rev.Med. 24:75-82.
52. Runion, H. 1975. Benzene in gasoline. J.,Am.Ind.Hyg.Assoc. 36:338-350.
53. Saita, G. 1973. Benzene induced hypoplastic anaemias and leukaemias.
IN Girdwood, R.H., ed. Blood Disorders Due to Drugs and Other
Agents. Amsterdam, Excerpta Medica. 1973. p. 127-146.
54. Saito, F.U., J.J. Kocsis, and R. Snyder. 1973. Effect of benzene
on hepatic drug metabolism and ultrastructure. Toxicol. Appl.
Pharmacol.26:209-217.
55. Sandberg, A.A. 1966. The chromosomes and causation of human cancer
and leukemia. Cancer Res. 26:2064-2081.
56. Selling, L. 1916. Benzol as a leucotoxin. Studies on the degeneration
and regeneration of the blood and haematopoietic organs. John Hopkins
Hosp.Reports. 17:83-142.
22
-------
57. Sellyei, M., and E. Kelemen. 1971. Chromosome study in a case
of granulocytic leukaemia with 'Pelgerisation1 7 years after
benzene pancytopenia. Eur.J.Cancer 7:83-85.
58. Sherwood, R.J. 1972. Evaluation of exposure to benzene vapour
during the loading of petrol. Brit.J.Ind.Med. 29:65-69.
59. Smolik, R., K. Grzybek-Hryncewicz, A.Lange, and W. Zatonski.
1973. Serum complement level in workers exposed to benzene,
toluene and xylene. Int.Arch.Arbeitsmed. 31:243-247.
60. Snyder, R., and J.J. Kocsis. 1975. Current concepts of chronic
benzene toxicity. CRC Grit.Rev.Toxicol. 3:265-288.
61. Thorpe, J.J. 1974. Epidemiologic survey of leukemia in persons
potentially exposed to benzene. J.Occup.Med. 16:375-382.
62. TLVs®. Threshold Limit Values for Chemical Substances and Physical
Agents in the Workroom Environment with Intended Changes for 1975.
1975. Cincinnati, Ohio, American Conference of Governmental
Industrial Hygienists.
63. Tough, I.M., and W.M. Court Brown. 1965. Chromosome aberrations
and exposure to ambient benzene. Lancet 1:684.
64. Tough, I.M., P.G. Smith, W.M. Court Brown, and D.G. Harnden. 1970
Chromosome studies on workers exposed to atmospheric benzene.
The possible influence of age. Eur.J.Cancer 6:49-55.
65. U. S. Department of Health, Education, and Welfare. Public Health
Service, National Institute for Occupational Safety and Health.
1974. Criteria for a Recommended Standard .... Occupational
Exposure to'Benzene. HEW Publ.No. (NIOSH) 74-137. Washington,
D.C., U.S. Government Printing Office.
66. Vigliani, E.G., and A. Forni. 1969. Benzene, chromosome changes
and leukemia. J.Occup.Med. 11:148-149.
67. Ward, J.M., J.H. Welsburger, R.S. Yamamoto, T. Benjamin, C.A.
Brown, and E.K. Weisburger. 1975. Long-term effect of benzene
in C57BL/6N mice. Arch.Environ.Health 30:22-25.
68. Yakushevich, Yu.Ye. 1973. Experimental data on the hygienic
evaluation of continuous and interrupted action of benzene
toluene and xylene. Gig.Sanit. 38(4):6-9 1973. [Translated by
Air Pollution Technical Information Center, Environmental
Protection Agency, Research Triangle Park, N.C. Translation
No. HS-135.]
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TECHNICAL REPORT DATA
(Please read Imttmcttons on the reverse before completing)
1. REPORT NO.
2.
3. RECIPIENT'S ACCESSION>NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
June 1976
Health Effects of Benzene: A Review
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Committee on Toxicology
9. PERFORMING ORGANIZATION NAME AND ADDRESS
National Research Council
National Academy of Sciences
2101 Constitution Avenue
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-01-2931
Environmental Protection Agency
Office of Toxic Substances
Washington, D.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
IS. SUPPLEMENTARY NOTES
16. ABSTRACT
Acute exposure to benzene produces toxic effects on the central nervous system;
however, in order to evaluate the chronic effects, consideration must be given to the
myelotoxlc and possible chromosome-damaging and leukemogenic effects of benzene. The
time required for expression of chronic benzene toxicity indicates a vast difference
in Individual sensitivity. Most cases of severe benzene intoxication have been
reported In workers exposed to rather high concentrations of benzene under somewhat
unhygienic working conditions. It is probable that all cases reporting a "leukemia
associated with benzene exposure" have resulted from exposure to rather high concen-
trations of benzene and other chemicals. It has been suggested that "benzene-induced
leukemia" may occur only in individuals who are highly sensitive because of genetic
constitution or because of synergistic action of other chemical or physical environ-
mental agents. 'A co-leukemogenic role for benzene would explain the failure to induce
leukemia in benzene-exposed animals. Based on available literature, It can be con-
cluded that benzene may be associated with leukemia; therefore, benzene must be con-
sidered a suspect leukemogen. Aplaatic anemia associated with benzene exposure may
well represent the most significant health hazard. More definitive data are required
for an accurate assessment of the myelotoxlc, leukemogenic and chromosome-damaging
effects of benzene.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Benzene
Health Effects of Benzene
IS. DISTRIBUTION STATEMENT
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
22. PRICE
EPA Form 2210-1 (t-73)
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