Journal of Toxiocology and Environmental Health (JTEH)

 A Comprehensive Evaluation of the Potential Health Risks Associated with Occupational and Environmental Exposure to Styrene

A comprehensive evaluation of the potential health risks associated with occupational and environmental exposure to styrene demonstrated that there does not appear to be a strong causal correlation between styrene and increased human cancer incidence.  However, styrene may produce acute neurotoxicity with symptoms such as drowsiness, headaches, and disturbance of balance at airborne concentrations above 100 ppm, as well as neurobehavioral effects, colour vision impairment, and hearing damage at lower exposure levels, according to research published in a special issue of the Journal of Toxicology and Environmental Health, Part B (Volume 5, Issues 1-2; 1-267) in 2002.

Styrene is produced in high volume with yield of over 10 billion pounds annually in the United States.  Styrene is used in building construction and packaging materials, tires and automotive parts, boats and tubs/shower stalls, carpet backings and paper coatings, household and office appliances, and battery casings.  Everyday exposures to styrene may occur through air, food, water, consumer products, and waste materials.  The primary sources of styrene are industrial and motor vehicle exhaust.  However, styrene is also naturally present in foods such as strawberries, beef, and spices, and  a natural by-product of both wine- and cheese-making processes.  In addition, styrene is  produced as a by-product of cigarette smoking.

Overall ambient air exposures to styrene are usually around 1 ppb. Non-occupational exposures to airborne styrene generally do not pose a reason for concern.  For oral exposure to styrene from food, both naturally occurring and as a result of migration from food packaging or food contact items, levels of exposure are relatively low and are not thought to produce adverse effects at these levels. 

In contrast, airborne concentrations of styrene in certain occupational environments might pose a reason for concern, depending on whether styrene is actually a human carcinogen.  Previous studies indicated a weak association between styrene and certain types of cancer while other investigations found no association.  While styrene itself is not listed as a carcinogen,  IARC lists one of its metabolites, styrene-7,8-oxide, as “probably carcinogenic to humans” (Group 2A).  This metabolite is thought to act directly on DNA, and thus, the potential for genotoxicity depends on the ability of an organism to convert styrene to styrene-7,8-oxide..

 If styrene is, in fact, a human carcinogen, then levels of the chemical may be too high in certain occupational environments.  Exposure to styrene in the reinforced plastics industry is markedly elevated.  However, if it is not a human carcinogen, the levels of styrene in these environments are not likely a cause for concern.  Non-cancer manifestations such as adverse effects on the central nervous system and  peripheral nervous system , are often reversible and generally occur at moderate severity, suggesting that styrene in most occupational environments is at acceptable, tolerable levels.

The aim of this special issue of the Journal of Toxicology and Environmental Health, Part B was to evaluate the existing scientific literature on styrene exposure, toxicity, epidemiology, and mode of action for the characterization of risks associated with general and occupational exposures to styrene. The special issue provides detailed descriptions of exposure conditions, toxicology, cancer and non-cancer health effects, and the mode of action of styrene. Further research areas suggested to better understand the human health impacts of styrene exposure including increased knowledge of  pharmacokinetics and pharmacodynamics, as well as additional study in the areas of neurotoxicity, ototoxicity, and immunotoxicity. 

Reference:

Cohen, J.T., Carlson, G., Charnley, G., Coggon, D., Delzell, E., Graham, J.D., Greim, H., Krewski, D., Medinsky, M., Monson, R., Paustenbach, D., Peterson, B., Rappaport, S., Rhomberg, L., Ryan, P.B., and Thompson, K. 2002. A Comprehensive Evaluation of the Potential Health Risks Associated with Occupational and Environmental Exposure to Styrene. Journal of Toxicology and Environmental Health, Part B 5:1-267.


Published eight times per year, the Journal of Toxicology and Environmental Health, Part B features in-depth critical reviews, both commissioned and unsolicited, with a focus on toxicology in general as well as in special interest fields such as target organ toxicities, immunotoxicology, risk assessment, carcinogenesis, mutagenesis, ecotoxicology, environmental factors affecting health, and aquatic toxicology.

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