STYRENE

100-42-5

Hazard Summary

CAUTION: Unless otherwise noted, the quantitative information on these fact sheets are from "EPA Health Effects Notebook for Hazardous Air Pollutants-Draft", EPA-452/D-95-00, PB95-503579, December 1994." Please conduct a current literature search and check the appropriate current online database for the most recent quantitative information.

• Acute (short-term) exposure to styrene in humans results in mucous membrane and eye irritation, and gastrointestinal effects.
• Chronic (long-term) exposure to styrene in humans results in effects on the central nervous system (CNS), such as headache, fatigue, weakness, and depression; peripheral neuropathy; and minor effects on some kidney enzyme functions and on the blood.
• The Reference Concentration (RfC) for styrene is 1 mg/m³.^a The U.S. Environmental Protection Agency (EPA) estimates that inhalation of this concentration or less, over a lifetime, would not likely result in the occurrence of chronic, noncancer effects.^b
• The Reference Dose (RfD) for styrene is 0.2 mg/kg/d.^c EPA estimates that consumption of this dose or less, over a lifetime, would not result in the occurrence of chronic, noncancer effects.
• Human studies are inconclusive on the reproductive and developmental effects of styrene; several studies did not report an increase in developmental effects in women who worked in the plastics industry, while an increased frequency of spontaneous abortions and decreased frequency of births were reported in another study.
• Several epidemiologic studies suggest there may be an association between styrene exposure and an increased risk of leukemia and lymphoma. However, the evidence is inconclusive due to confounding factors. Animal studies have produced both negative and positive results. The International Agency for Research on Cancer (IARC) has classified styrene as a Group 2B, possible human carcinogen. EPA's Office of Research and Development has updated previous assessments on the carcinogenic potential of styrene and concluded that styrene is appropriately classified in Group C,"possible human carcinogen".(7) The EPA is currently reviewing the potential of styrene to cause cancer.

^a Milligrams per cubic meter is the unit of measurement for chemicals in air.
^b The RfC is not a direct estimator of risk but rather a reference point to gauge the potential effects. Exceedance of the RfC does not imply that an adverse health effect would necessarily occur. As the amount and frequency of exposures exceeding the RfC increase, the probability of adverse health effects also increases.
^c Milligram per kilogram per day is one way to measure the amount of the contaminant which is consumed in food.

Please Note: The main sources of information for this fact sheet are EPA's IRIS, which contains information on inhalation chronic toxicity of styrene and the RfC, and oral chronic toxicity and the RfD, and the Agency for Toxic Substances and Disease Registry's (ATSDR's) Toxicological Profile for Styrene. Other secondary sources include the Hazardous Substances Data Bank (HSDB), a database of summaries of peer-reviewed literature, and the Registry of Toxic Effects of Chemical Substances (RTECS), a database of toxic effects that are not peer reviewed.

Environmental/Occupational Exposure

• Indoor air is the principal route of styrene exposure for the general population. Average indoor air levels of styrene are in the range of 1 to 9 g/m³, attributable to emissions from building materials, consumer products, and tobacco smoke. (1)
• Ambient air in urban locations contains styrene at average concentrations of 0.29 to 3.8 g/m³, while styrene in rural and suburban air has been measured at 0.28 to 0.34 g/m³. (1)
• Occupational exposure to styrene occurs in the reinforced plastics industry and polystyrene factories. (1)
  

Assessing Personal Exposure

• Laboratory tests can determine styrene by measuring the breakdown products in the urine. However, these tests are only useful for detecting very recent exposures. (1)

Health Hazard Information

• Acute (short-term) exposure to styrene in humans results in respiratory effects, such as mucous membrane irritation, eye irritation, and gastrointestinal effects. (1,2)
• Tests involving acute exposure of animals, such as the LC₅₀ and LD₅₀ tests in rats and mice, have shown styrene to have low to moderate toxicity by inhalation and oral exposure. (3)

• Chronic (long-term) exposure to styrene in humans results in effects on the central nervous system, with symptoms such as headache, fatigue, weakness, and depression, peripheral neuropathy, minor effects on some kidney enzyme functions and on the blood. (1-3)
• Animal studies have reported effects on the central nervous system, liver, kidney, and eye and nasal irritation from inhalation exposure to styrene. (1)
• The RfC for styrene is 1 mg/m³ based on CNS effects in occupationally exposed workers. (5)
• EPA has medium confidence in the study on which the RfC was based because, although the study documents concentration-response relationships of CNS effects in a relatively small worker population, the results are consistent with a number of other studies showing central effects in chronically exposed worker populations; medium to high confidence in the database because the chronic laboratory animal studies addressing noncancer endpoints were not available, although a number of human exposure studies support the choice of critical effect; and, consequently, medium confidence in the RfC. (5)
• The RfD for styrene is 0.2 mg/kg/d based on red blood cell and liver effects in dogs. (5)
• EPA has medium confidence in the principal study on which the RfD was based because it was well done and the effect levels seem reasonable, but the small number of animals/sex/dose prevents a higher confidence; medium confidence in the database because it offers strong support, but lacks a bona fide full-term chronic study; and, consequently, medium confidence in the RfD. (5)

• Human studies have not reported an increase in developmental effects in women who worked in the plastics industry, while an increased frequency of spontaneous abortions and a decreased frequency of births were reported in a study on the reproductive effects of styrene in humans. However, these studies are not conclusive, due to the lack of exposure data and confounding factors. (1,2)
• Animal studies have not reported developmental or reproductive effects from inhalation exposure to styrene. (1)

• Several epidemiologic studies suggest that there may be an association between styrene exposure and an increased risk of leukemia and lymphoma. However, the evidence is inconclusive due to multiple chemical exposures and inadequate information on the levels and duration of exposure. (1,2,7)
• Animal cancer studies have produced variable results and provide limited evidence for carcinogenicity.(7)
• IARC has classified styrene as a Group 2B, possibly carcinogenic to humans. (1)
• Styrene oxide is a reactive metabolite of styrene and shows positive carcinogenic results in oral exposure bioassays. Styrene oxide has been detected in workers exposed to styrene.(7) IARC has classified this metabolite as a probable carcinogen. (1)
• EPA's Office of Research and Development has updated previous assessments on the carcinogenic potential of styrene and concluded that styrene is appropriately classified in Group C, "possible human carcinogen".(7) The EPA is currently reviewing the potential of styrene to cause cancer.
  

Physical Properties

• Styrene is a colorless liquid that has a sweet smell. (1)
• The odor threshold for styrene is 0.32 ppm. (6)
• The chemical formula for styrene is C₈H₈, and the molecular weight is 104.16 g/mol. (1)
• The vapor pressure for styrene is 5 mm Hg at 20 C, and its octanol/water partition coefficient (Log K_ow) is 2.95. (1)

Uses

• Styrene is used predominately in the production of polystyrene and resins. Styrene is also used as an intermediate in the synthesis of materials used for ion exchange resins and to produce copolymers. (1)

Health Data from Inhalation Exposure

^a Health numbers are toxicological numbers from animal testing or risk assessment values developed by EPA.
^b Regulatory numbers are values that have been incorporated in Government regulations, while advisory numbers are nonregulatory values provided by the Government or other groups as advice.
^c This NOAEL is from the critical study used as the basis for the EPA RfC.

References

1. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Styrene (Draft). U.S. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. 1992.
2. U.S. Department of Health and Human Services. Hazardous Substances Data Bank (HSDB, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.
3. U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances (RTECS). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.
4. E.J. Calabrese and E.M. Kenyon. Air Toxics and Risk Assessment. Lewis Publishers, Chelsea, MI. 1991.
5. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Styrene. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1993.
6. J.E. Amoore and E. Hautala. Odor as an aid to chemical safety: Odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. Journal of Applied Toxicology, 3(6):272-290. 1983.
7. Memorandum from Robert J. Huggett,PhD, AA for Office of Research and Development to Mary D. Nichols, AA for Air and Radiation, USEPA, on Classification of Styrene. July 19, 1995. Available in Docket No. A-91-64, phone 202-260-7548, and on the Technology Transfer Network BBS, modem number 919-541-5742, TELNET ttnbbs.rtpnc.epa.gov.