One way benzene may enter the body is by inhalation
of contaminated air into the lungs. Studies with human volunteers
indicate that inhaled benzene vapors are rapidly absorbed from the
lungs into the bloodstream where they can then be transported throughout
the body. The highest absorption (up to eighty percent) has been
noted during the first few minutes of exposure (ATSDR, 1996a). Studies
where human volunteers were exposed to high levels of benzene vapors
for a few hours have noted that approximately half of the vapors
inhaled are retained and absorbed from the lungs (EM, 1995).
Benzene is soluble in fat. Absorbed benzene
can temporarily be stored (accumulate) in bone marrow and fat and
slowly be re-released to the blood stream. The amount of body fat
and degree of physical activity influence how quickly stored benzene
will be re-released.
About half of the benzene absorbed into the
blood stream leaves the body unchanged in exhaled air within about
36 hours after exposure has stopped (EM, 1995). Here again, timing
is influenced by the amount of body fat and degree of physical activity
(EM, 1995). The remaining fifty percent is broken down into other
compounds (metabolites) in the liver and bone marrow. Some of these
metabolites are believed to be responsible for some of the adverse
blood effects associated with long term inhalation of high levels
of benzene vapors (EM, 1995). Most of the metabolites leave the
body through the urine within 48 hours after short term exposure
stops (ATSDR, 1996a).
The majority of information on potential health
effects that may be associated with inhalation of benzene vapors
comes from studies of workers who were exposed to high levels of
benzene vapors for extended periods of time. The general public
is not expected to experience such high exposures.
Brief exposure (less than 10 minutes) to highly
elevated levels of benzene vapors (about 20,000 ppm, 64,000,000
ug/m 3 ) can result in death (ATSDR, 1996a). Inhalation of between
700 and 3,000 ppm (2,200,000 to 9,600,000 ug/m 3 ) can significantly
depress the central nervous system and result in dizziness, drowsiness,
rapid heart rate, headaches, tremors, confusion and unconsciousness
(ATSDR, 1996a; EM, 1995). In many instances, recovery from such
central nervous system effects has been noted once exposure stops
and a person starts to breathe fresh air (ATSDR, 1996a). However,
recovery time will vary depending on the amount of benzene inhaled
and stored in the body.
Studies of people, especially workers, indicate
that inhalation of elevated levels of benzene for long periods of
time may damage the tissues that form blood cells, especially the
bone marrow. Anemia, excessive bleeding and leukemia (cancer of
the blood forming organs) may result. Blood processes may return
to normal if exposure has been limited and the person returns to
breathing fresh air (ATSDR, 1996a). Prolonged exposure to elevated
levels of benzene may also weaken the immune system thus decreasing
the body's ability to fight infection and perhaps ward off cancer.
Exposure to benzene has also been associated with damage to the
body's genetic material (chromosomes).
Limited studies of women exposed to elevated
levels of benzene, and a mix of other volatile chemicals, in the
work place suggest that such exposure may effect the reproductive
organs and perhaps impair fertility. However, because exposure was
to more than one chemical at a time, it is not known which chemical
or combination of chemicals may be responsible for the health effects
noted. The impact of such exposure on a developing human fetus is
Ingested benzene is also rapidly absorbed into
the blood stream. Ingestion of food and/or drink containing high
levels of benzene may result in vomiting, stomach irritation, dizziness,
sleepiness, convulsions, rapid heart rate, coma, and death (ATSDR,
1996a). The potential health effects that may be associated with
long term consumption of foodstuffs containing lower levels of benzene
have not been identified. However, long term experimental ingestion
studies with laboratory animals have noted damage to the blood and
immune system and in some instances, result in cancer (ATSDR, 1996a).
Dermal contact with benzene can cause skin irritation
and result in redness and sores. Benzene canalso cause eye irritation
and corneal damage if it comes in contact with the eyes.
Long term experimental studies with laboratory
animals ingesting food and drink with elevated levels of benzene
noted damage to the blood and immune systems and in some instances
increased incidences of cancer (ATSDR, 1996a). Experimental studies
with pregnant laboratory animals breathing in large amounts of benzene
for long periods of time have noted damage to the developing fetus.
It is not known if human fetuses may be similarly effected.
Benzene has been classified as Class A: Known
Human Carcinogen by the United States Environmental Protection Agency
and as Group 1: Human Carcinogenic by the International Agency for
Research on Cancer.
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Last Updated: 1/31/03