CAS No. 100425
Styrene is a high production, hydrocarbon chemical used to manufacture of polystyrene resins, which are widely used in plastic packaging, disposal cups and containers, insulation, adhesives, and in composite materials such as fiberglass. It is also used to produce synthetic rubber and latex. Because styrene is synthesized largely from ethylbenzene, it may be present in products made from styrene. Styrene is commonly detected in urban air, especially near industrial sites where it is produced and used, and in high motor vehicle traffic areas. Air concentrations of styrene may be greater indoors than outdoors, as a result of emissions from photocopiers and laser printers, cigarette smoke, and consumer products in the home (ATSDR, 2010; Wallace et al., 1987). Styrene does not persist in the aquatic or soil environments because of its volatility and is rarely detected in U.S. groundwater or drinking water supplies (USGS, 2006).
For the general population, inhalation of styrene is the primary exposure route. Trace amounts can be ingested when styrene migrates from packaging into foods. Styrene is well absorbed by inhalation, ingestion or dermal routes. Workplace exposure may occur during the production of styrene or products derived from styrene. After absorption, styrene is metabolized within hours by the liver. The main urinary excretion products are mandelic acid and phenylglyoxylic acid, which have been used in monitoring workplace exposure (ATSDR, 2010; Brugnone et al., 1993; Ramsey et al., 1980). The U.S. EPA has established a drinking water and other environmental standards for styrene. Workplace standards and guidelines for styrene have been established by OSHA and ACGIH, respectively. The ACGIH recommends biological exposure indices to monitor workplace exposure.
Human health effects from styrene at low environmental doses or at biomonitored levels from low environmental exposures are unknown. Eye and upper respiratory tract irritation occur after several hours of exposure to air concentrations that exceed the occupational standard for workers. Several studies of chronic occupational exposure to styrene reported neurological effects, including altered color vision, vestibular dysfunction, impaired hearing and altered performance on neuropsychological and neurophysiological tests (ATSDR, 2010). Various studies of workers with styrene exposure have not provided clear evidence of an increased risk for reproductive or developmental effects, or cancer (ATSDR, 2010), but increased serum prolactin levels have been correlated with levels of its urinary metabolite (Mutti et al., 1984) and levels of styrene in blood (Luderer et al., 2004) in both male and female workers.
Animal carcinogenicity studies have shown variable results, including lung tumors in mice and no increase in tumor incidence in rats (IARC, 2002). Styrene-7, 8-oxide, a biological metabolite of styrene and also a chemical used in making fragrances and epoxy resins, is classified as a probable human carcinogen by IARC and is reasonably anticipated to be human carcinogen by NTP. Styrene is classified as a possible human carcinogen by IARC. Additional information about external exposure (ie., environmental levels) and health effects is available from ATSDR at http://www.atsdr.cdc.gov/toxprofiles/index.asp.
Levels of styrene in blood reflect recent exposure. In NHANES 2001-2002, 2003-2004 and 2005-2006 subsamples, levels of styrene in blood are of a similar range to those found in a non-representative sample of adults in NHANES III (1988-1994) (Ashley et al., 1994; Churchill et al., 2001). Other small studies of the U.S. general population have reported similar or slightly higher blood styrene levels (Bonanno et al., Buckley, et al., 1997; Sexton et al., 2005 and 2006). Blood styrene levels can be three to fourfold higher in smokers than nonsmokers (Ashley et al., 1995; Bonanno et al., 2001), but exposure to environmental tobacco smoke or vehicle exhaust in urban areas has not been associated with higher blood styrene levels (Bonanno et al., 2001; Romieu et al., 1999). Workers exposed to styrene can have blood levels that are 25 times higher than those in the general population (Brugnone et al., 1993; Triebig et al., 1985).
Finding a measureable amount of styrene in blood does not imply that the level of styrene causes an adverse health effect. Biomonitoring studies of blood styrene can provide physicians and public health officials with reference values so that they can determine whether or not people have been exposed to higher levels of styrene than levels found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.
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