Benzene (C6H6) may sometimes be referred to as: benzol 90, pyrobenzol, phene, coal naphtha, and polystream. It is a clear, colorless, flammable, and liquid with a definite distinctive sweet odor, mixture of hydrocarbons, chiefly alkanes such as pentane and hexane. It evaporates quickly in air and is partially soluble in water. The modern symbol implies the modern understanding that the double bonds are delocalized and shared by all the carbons in the ring. It was widely used until it was determined to be carcinogenic. Benzene was first discovered in 1825 by Faraday, who isolated it from a liquid condensed by compressing oil gas. Today, most (about 98%) benzene is commercially derived from petrochemical and petroleum refining industries. Benzene is a by-product of various combustion processes, such as forest fires and the burning of wood, garbage, organic wastes, and cigarettes. It is obtained by the fractional distillation of petroleum. It is also released to the air from crude oil seeps and volatilizes from plants.
In the 19th and early-20th centuries, benzene was used as an after-shave lotion because of its pleasant smell. Prior to the 1920s, benzene was frequently used as an industrial solvent, especially for degreasing metal. As its toxicity became obvious, benzene was supplanted by other solvents, especially toluene (methyl benzene), which has similar physical properties but is not as carcinogenic. In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee. This discovery led to the production of Sanka (the letters "ka" in the brand name stand for kaffein). As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking. Consequently, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely-used antiknock additive. With the global phase out of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. Currently, worldwide production of benzene is estimated at approximately 15 million tons. Benzene is one of the world's major commodity chemicals. Its primary use (95% of production) is as an intermediate in the production of other chemicals, predominantly ethyl benzene (for styrofoam and other plastics), cumene (for various resins), and cyclohexane (for nylon and other synthetic fibers). Benzene is an important raw material for the manufacture of synthetic rubbers, gums, lubricants, dyes, and pharmaceutical and agricultural chemicals; it is also found in consumer products such as glues, paints, and marking pens.
Benzene can be present in the soil, air, or water and thus, is ubiquitous in the environment, having been measured in air, water, and human biological samples. The major environmental sources include automobile exhaust, automobile refueling, hazardous waste sites, underground storage tanks that leak, waste water from industries that use benzene, chemical spills, chemical manufacturing sites, and petrochemical and petroleum industries. Benzene is primarily exhaled through the lungs, unchanged or excreted as metabolites in the urine. Benzene has long been recognized as a carcinogen and recent concern has centered on the effects of continuous exposure to low concentrations of benzene both occupationally and environmentally.
With short-term exposure
- Contact with low to moderate levels of benzene for a short time can cause headaches, vomiting, disorientation, shakiness, elevated heart rate, and loss of consciousness.
- Causes depression of the central nervous system, marked by drowsiness, dizziness, headache, nausea, loss of coordination, confusion and unconsciousness.
- Eating or drinking foods containing high levels of benzene can cause vomiting, irritation of the stomach, dizziness, sleepiness, convulsions, rapid heart rate, and death.
- Exposure to 50 to 150 ppm produces headache, and tiredness.
- Nose and throat irritation have also been reported following short-term exposure.
- Animal evidence has shown that benzene is moderately irritating when comes in skin contact.
- The vapour can be irritating to the eyes. Animal evidence indicates that splashes of benzene in the eyes will be moderately irritating but will not cause permanent injury.
With long-term exposure
- Very high levels of exposure can be fatal and exposure to approximately 20,000 ppm for 5 to 10 minutes may result in death.
- Prolonged or repeated contact causes skin effects like: redness, dryness, cracking (dermatitis) due to the defatting action of this solvent.
- Benzene also damages the bone marrow, where new blood cells are produced, resulting in aplastic anemia, which can lead to leukemia.
- Studies have found changes in the immune system.
- Studies suggest that benzene may cause effects on the peripheral nerves and/or spinal cord.
- Symptoms included an increased incidence of headaches, fatigue, difficulty in sleeping and memory loss among workers with significant exposures.
- The International Agency for Research on Cancer (IARC) has concluded that there is sufficient evidence for carcinogenicity of benzene to humans. Benzene exposure has been associated with cancer of the lymph system (lymphoma), lung cancer and bladder (urothelial) cancer.
- People who are exposed to it over a long period of time are at the highest risk for developing benzene-related illnesses, which range from anemia to cancer.
- High occupational exposures to benzene may be related to menstrual and reproductive problems in women.
- Limited animal evidence suggests that benzene may affect reproductive organs at exposure levels which also cause significant toxicity.
- Animal evidence indicates that benzene is not teratogenic, but is fetotoxic at exposure levels which also resulted in mild maternal toxicity but there is no conclusive evidence that it affects the human fetus.
The US Environmental Protection Agency has set the maximum permissible level of benzene in drinking water at 0.005 milligrams per liter (0.005 mg/L). The US Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek.