Styrene has a number of alternate names, including ethenylbenzene, vinylbenzene, phenylethene, phenylethylene, styrol, cinnamene, styropol, styrolene, and Diarex HF 77.
Low levels of styrene occur naturally in some fruits, nuts, and vegetables, including cranberries, bilberries, currants, grapes, parsley, roasted filberts, and peanuts. It can also be found in vinegar, whiskey and other alcoholic beverages, coffee, tea, milk, and dairy products. Most of the styrene used in current industry, however, is made from ethylbenzene, a colorless liquid found in coal tar and petroleum. The removal of hydrogen from ethylbenzene, a chemical reaction known as dehydrogenation, results in liquid styrene with benzene and toluene as by-products. The liquid styrene is usually either colorless or slightly yellow. Unless it is treated with inhibitor chemicals, however, styrene is a monomer that will polymerize (form large molecules consisting of groups of monomers) in storage.
Pure styrene is flammable and gives off irritating fumes in a fire. It evaporates at 68°F (20°C) and can form an explosive mixture of vapor and air at temperatures above 87°F (31°C). It boils at 293°F (145°C) and freezes at -23.1°F (-30.6°C). Because of its volatility, styrene must be stored and handled with care. In its liquid form, it is a marine pollutant, which means that it is toxic to aquatic organisms if it leaks into or is disposed of in bodies of water.
Styrene was discovered in 1839 by Johann Eduard Simon (1789–1856), a German apothecary (pharmacist), when he distilled it from storax, resin obtained from a sweetgum tree. Simon named the liquid he obtained styrol. Several days later, he found that the liquid had polymerized on exposure to air and light, forming a hard substance that he called styrol oxide, subsequently known as polystyrene. The chemical formula (C8H8) of styrene was identified by August von Hofmann (1818–1892) in 1845, and polystyrene was identified as a polymer of styrene by the French chemist Pierre Marcellin Berthelot (1827–1907) in 1866.
The modern method of producing styrene in industrial quantities by dehydrogenating ethylbenzene was developed in the 1930s in the United States by the Dow Chemical Company and in Germany by I.G. Farben. A newer method derives styrene from ethylbenzene first treated with oxygen to form ethylbenzene hydroperoxide. Two other methods produce styrene from toluene and methanol or by adding benzene to ethane in a dehydrogenation reactor, but these two approaches were considered inefficient as of 2018 and were undergoing further development.
Because of the use of styrene in producing polystyrene, most of the world's inhabitants have come into contact with some form of the latter, given its use in industries as different as food service and storage, construction and engineering, automobile and consumer goods manufacturing, and medical equipment. As of 2018, about 15 million metric tons of liquid styrene were manufactured worldwide each year. People's exposure to styrene varies widely: low levels of exposure come from consuming foods or beverages containing styrene; it is absorbed from packaging materials; it is inhaled when indoor air is contaminated by styrene vapor; and eye, skin, or lung irritation results from workplace exposure. According to the Agency for Toxic Substances and Disease Registry (ATSDR), outdoor air in North America contains between 0.06 and 4.6 parts per billion (ppb) of styrene vapor, whereas indoor air contains between 0.07 and 11.5 ppb. Workers in industries that produce or use styrene, particularly those in the reinforced-plastics industry, are at greatest risk of serious health effects.
More than half of the styrene that is produced commercially is used in the manufacture of polystyrene, a plastic widely used to make packing materials (called peanuts), containers for fast food, DVD and CD cases, lids, bottles, trays, and disposable cutlery. Styrene is also used to make synthetic rubbers and specialty plastics, which in turn are used in the manufacture of fiberglass, insulation, plastic pipes, shoes, tires and other parts for boats, airplanes, and automobiles, carpet backing, thermosetting plastics, and food containers.
As of 2018, styrene was also used as a biomarker for detecting evidence of smoking in human blood. It is one of several volatile organic compounds (VOCs) that can be measured for this purpose. On average, smokers in the United States have blood levels of styrene that are 8 times higher than those of nonsmokers.
Styrene may enter the human or natural environment in several ways:
Exposure to styrene can produce the following symptoms:
Styrene is suspected to be a carcinogen but had not been shown definitively as of 2018 to cause cancer; one reason for the uncertainty is that most people exposed to styrene in the workplace are exposed to a mixture of other chemicals as well. In addition, there is only limited evidence as of 2018 that styrene causes cancer in animals. It is known, however, that styrene is metabolized in the human body to form styrene-7,8oxide, a compound that binds to DNA and appears to have genetic effects.
The International Agency for Research on Cancer (IARC) published its last monograph on styrene in 2002 and met at the end of March 2018 to determine whether the monograph required major changes; it considered styrene “possibly carcinogenic to humans.” The Environmental Protection Agency (EPA) did not as of 2018 have a cancer classification for styrene but has collected data on it since 1987 as part of the agency's Integrated Risk Information System (IRIS). The National Toxicology Program (NTP) has stated that styrene is “reasonably anticipated to be a human carcinogen.”
Diagnosis of the effects of styrene exposure in adults is almost always based on a personal history of workplace exposure or a known recent industrial accident involving explosion or spillage of styrene.
The National Institute of Occupational Safety and Health (NIOSH) recommends the following measures to prevent health problems from exposure to styrene:
NIOSH recommends the following treatments for exposure to styrene:
Most people exposed to styrene vapor outside the workplace do not suffer lasting ill effects. Little is known, however, about lethal dosages in humans: One source published in 1978 estimated that 30 minutes of exposure to styrene vapor in a concentration of 10,000 parts per million (ppm) would be fatal. There were no known cases of death resulting from ingesting liquid styrene as of 2018.
Precautions for the safe handling and storage of styrene include the following:
See also Benzene ; Benzene and benzene derivatives exposure .
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Centers for Disease Control and Prevention (CDC), 1600 Clifton Rd., Atlanta, GA, 30329, (800) CDC-INFO, CDC-INFO, http://www.cdc.gov/ .
International Agency for Research on Cancer (IARC), 150 Cours Albert Thomas, Lyon, France, 69372 Lyon CEDEX 08, +33 04 72 73 84 85, http://www.iarc.fr .
International Programme on Chemical Safety (IPCS), Avenue Appia 20, Geneva, 1202, Switzerland, +41 22 791211, http://www.who.int/ipcs/en/ .
National Institute of Environmental Health Sciences (NIEHS), 111 T. W. Alexander Dr., Durham, NC, 27709, (919) 541-3345, Fax: (301) 480-2978, firstname.lastname@example.org, https://www.niehs.nih.gov .
U.S. Environmental Protection Agency (EPA), 1200 Pennsylvania Ave., NW, Washington, DC, 20460, (202) 564-4700, https://www.epa.gov .
Rebecca J. Frey, PhD