Health Concerns

Benzene

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 not known.

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