Benzene is a simple cyclic organic compound found in a colorless liquid form with a sweet (aromatic) odor. It is formed through incomplete combustion of organic materials. Benzene was first discovered and isolated from coal tar in the 19th century. Today, benzene is made mostly from petroleum sources.
Benzene found in the environment is from both human activities and natural processes. Various industries use benzene to make other chemicals, such as styrene, cumene (for various resins), and cyclohexane (for nylon and synthetic fibers). Benzene is also used for the manufacturing of some types of rubbers, lubricants, dyes, detergents, drugs, and pesticides. Benzene is also a natural part of crude oil and gasoline, and cigarette smoke.
Industrial processes are the main sources of benzene in the environment. Benzene levels in the air increase from emissions from burning coal and oil, benzene waste and storage operations, motor vehicle exhaust, evaporation from gasoline service stations, and use of industrial solvents. Industrial discharge, disposal of products containing benzene, and gasoline leaks from underground storage tanks can release benzene into water and soil. Natural sources of benzene, which include volcanoes and forest fires, also contribute to the presence of benzene in the environment.
Benzene can pass into air from water and soil surfaces. Once in the air, benzene reacts with other chemicals and breaks down within a few days. Benzene in the air can attach to rain or snow and be carried back down to the ground. Benzene in water and soil breaks down more slowly. Benzene is slightly soluble in water and can pass through the soil into underground water. Benzene in the environment does not build up in plants or animals.
Most people are exposed to a small amount of benzene on a daily basis. Exposure of the general population to benzene is mainly through inhalation. The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions. Vapors (or gases) from products that contain benzene, such as glues, paints, furniture wax, and detergents can also be a source of exposure.
Background levels of benzene in air range from 1.2 to 14.6 ppb. People living in cities or industrial areas are generally exposed to higher levels of benzene in air than those living in rural areas. Benzene levels in the home are usually higher than outdoor levels. People living around hazardous waste sites, petroleum refining operations, petrochemical manufacturing sites, or gas stations may be exposed to higher levels of benzene in air (up to 16 246 ppb).
The average smoker (32 cigarettes per day) takes in about 1.8 milligrams (mg) of benzene per day (12 to 48 g/cigarette). This is about 10 times the average daily intake of nonsmokers. When exposed to high levels of benzene in air, about half of the benzene breathed in passes through the lining of the lungs and enters the bloodstream.
For most people, the level of exposure to benzene through food, beverages, or drinking water is not as high as through air. Typical drinking water contains less than 0.1 ppb benzene. Benzene has been detected in some bottled water, liquor, and food (at concentration up to 2.1 mg/kg). Leakage from underground gasoline storage tanks or from landfills and hazardous waste sites containing benzene can result in benzene contamination of well water. People with benzene-contaminated tap water can be exposed from drinking the water or eating foods prepared with the water. In addition, exposure can result from breathing in benzene while showering, bathing, or cooking with contaminated water. A survey of Ontario surface water found benzene concentrations ranging from below 0.1 g/l to 4.3 g/l.
Most people can begin to smell benzene in air at 1.5-4.7 parts of benzene per million parts of air (ppm). Most people can begin to taste benzene in water at 0.5-4.5 ppm.
Animal studies show that benzene absorbed through ingestion behaves similarly in the body to benzene that enters through the lungs. A small amount of benzene will enter the body by absorption through the skin and into the bloodstream during skin contact with benzene or benzene-containing products. Once in the bloodstream, benzene travels throughout the body and can be temporarily stored in the bone marrow and fat. The liver and bone marrow convert benzene into metabolites which may cause some of the harmful effects of benzene exposure. Most of the metabolites of benzene are excreted in the urine within 48 hours following exposure. Unmetabolized benzene is eliminated by exhalation.
Benzene is a flammable liquid. Poisonous gas is produced in fire. Benzene vapor is heavier than air and may travel a distance to cause a fire or explosion far from the source.
Benzene is moderately soluble in water; 1 to 1,000 mg will dissolve in a liter of water. Benzene is slightly persistent in water, with a half-life of between 2 to 20 days. Because of its high volatility, approximately 99.5% of benzene ends up in air; the rest will dissolve in the water.
| BENCHMARKS | |
Canadian Water Quality Guidelines | |
| Drinking water | 0.005 mg/l |
| Protection of freshwater aquatic life | 0.3 mg/l |
Ontario Water Quality Objectives | |
| Interim PWQO (under development) | 0.1 mg/l |
U.S. EPA | |
| Maximum permissible level drinking water |
0.005 mg/L |
| Spills or accidental releases into the environment of 10 pounds or more of benzene must be reported. | |
OSHA | |
| Legal airborne permissible exposure limit (PEL) workplace air | 1 ppm
8-hour workday, 40-hour workweek 5 ppm should not be exceeded in any 10 minute period |
ACGIH | |
| Recommended airborne exposure limit | 10 ppm
averaged over an 8 hour workshift |
NIOSH | |
| Recommended airborne exposure limit | 1.0 ppm should not be exceeded during any 60 minute period. |
LC50 Values | |
| Rainbow trout | 5.3 mg/L (96hr) 8.3 mg/L (27 day exposure from 30 minutes after fertilization) |
| Daphnia magna | 31.2 mg/L (48 hr) |
| Damselfly nymph | 10 mg/L (48 hr) |
| Coho salmon | 9 mg/L (96 hr) |
| Rats | 44 500 mg/m3 (4 hr - inhalation) 32 500 mg/m3 (7 hr - inhalation) |
HUMAN HEALTH
The amount of benzene and the length of time of the exposure determine whether harmful health effects will occur and the type and severity of these health effects.
Brief exposure (5-10 minutes) to very high levels of benzene in air (10,000-20,000 ppm) can result in death. Lower levels (700-3,000 ppm) can cause drowsiness, dizziness, rapid heart rate, headaches, tremors, confusion, and unconsciousness. In most cases, people will stop feeling these effects when they stop being exposed and begin to breathe fresh air.
Inhalation of benzene for long periods may cause harmful effects in the tissues that form blood cells, especially the bone marrow. These effects can disrupt normal blood production and cause a decrease in important blood components. A decrease in red blood cells can lead to anemia. Reduction in other components in the blood can cause excessive bleeding. Blood production may return to normal after exposure to benzene stops. Excessive exposure to benzene can be harmful to the immune system, increasing the chance for infection and perhaps lowering the body's defense against cancer.
Eating or drinking foods containing high levels of benzene can cause vomiting, irritation of the stomach, dizziness, sleepiness, convulsions, rapid heart rate, coma, and death. The health effects that may result from eating or drinking foods containing lower levels of benzene are not known.
Skin contact may cause redness and sores. Long term exposure may cause drying and scaling of the skin. Skin contact may also cause overexposure.
Benzene in the eyes may cause general irritation and damage to the cornea.
Exposure to benzene may also be harmful to the reproductive organs. Some women workers who breathed high levels of benzene for many months had irregular menstrual periods and a decrease in the size of their ovaries.
Exposure to benzene has also been linked with chromosomal damage.
Benzene crosses the placenta in humans but no effects on the fetus have been reported.
Benzene is a known human carcinogen. Benzene has been shown to cause cancer of the blood-forming organs (leukemia). There may be no safe level of exposure to a carcinogen.
Benzene is a mutagen and a possible human teratogen.
MEDICAL TESTS
Complete blood count.
Urinary phenol.
A test exists that measures benzene in the breath; this test must be done shortly after exposure.
Benzene can also be measured in the blood, however, since benzene disappears rapidly from the blood, measurements are only accurate for recent exposures.
In the body, benzene is converted to products called metabolites some of which can be measured in the urine. This test must be performed shortly after exposure and may not be a reliable indicator of the levels of exposure to benzene because the metabolites may be originate from other sources.
ANIMAL HEALTH
In animals, exposure to food, water or air contaminated with benzene can damage the blood and the immune system and cause neurological effects, behavioural disturbances and cancer.
Studies with pregnant animals show that breathing benzene has harmful effects on the developing fetus. These effects include low birth weight, delayed bone formation, and bone marrow damage. Concentrations that may not be toxic to the mother may be toxic to the embryo and fetus.
Benzene has high acute and chronic toxicity to aquatic life.
The concentration of benzene found in fish tissues is expected to be somewhat higher than the average concentration of benzene in the water from which the fish was taken.
Benzene can cause death in plants and roots and membrane damage in leaves of various agricultural crops.
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