The vast majority of ethylbenzene exposure arises from petroleum sources. The contributions of ethylbenzene exposure from the production and uses of styrene are relatively very small.
A comprehensive risk assessment of the potential human exposures to ethylbenzene was performed as part of an ethylbenzene risk assessment that was published in 2015. SIRC updated the evaluation of exposure in 2020 to assist in present-day assessments of human health risk.
The following sections review the current knowledge of ethylbenzene exposure to workers and the general public. Because these sections summarize the exposure information, specific references are not provided but are available upon request.
Ethylbenzene exposures in workplaces that manufacture styrene are well below occupational guidelines.
Exposure to ethylbenzene occurs mainly in two types of workplaces: (1) the refinery industry where ethylbenzene is a natural constituent of crude oil and refined petroleum products, and (2) the styrene industry where commercially produced ethylbenzene is used in the manufacturing of styrene.
Occupational exposure to ethylbenzene is common in jobs that work with petroleum products, such as oil refining, handling of gasoline and other fuels, asphalt road paving, automotive service technicians, truck drivers, and occupations that use products containing mixed xylenes.
The primary route of exposure of ethylbenzene to workers is by inhalation. Workers may also come into skin contact with ethylbenzene, however compared to the inhalation route where uptake through the lungs is high, its high evaporation rate from the skin results in only minimal amounts of ethylbenzene (< 5%) that pass through the skin into the body. Air exposure levels for oil and gas workers are highly variable with reported concentrations ranging from low parts per billion (ppb) to low parts per million (ppm) levels. A 2021 survey of U.S. styrene manufacturing workers found the daily (8-hour time weighted) average exposures to ethylbenzene did not exceed 0.3 ppm and the upper confidence limit on their exposures did not exceed 0.9 ppm. These exposures are a twentieth or more lower than the current lowest occupational exposure limit, 20 ppm.
General Public Exposure
The primary routes of ethylbenzene exposure for the general public are by inhalation of ambient and indoor air and ingestion of food containing amounts of ethylbenzene.
The general public is exposed to very low levels of ethylbenzene from air. The highest inhaled ethylbenzene concentrations occur in smokers.
Ethylbenzene is often detected in ambient air as a result of releases from refinery and chemical industrial processes and products, and human activities. Annual average ethylbenzene air concentrations reported in the U.S. from 2014 to 2018 for rural, suburban, and urban environments were 0.02, 0.06, and 0.08 ppb, respectively.
Indoor air concentrations of ethylbenzene are important because concentrations of most volatile organic chemicals (VOCs), including ethylbenzene, are typically higher in buildings than in outdoor air and because most individuals spend the majority of their time indoors. Ethylbenzene present in residential and other building indoor air can arise from multiple indoor and outdoor sources, such as automobile sources and exhaust, tobacco smoke, certain household products or hobby materials that contain mixed xylenes, and styrenic building and furnishing materials. Since the mid-2000s, the typical median styrene air concentrations inside homes are reported to be below 0.25 ppb, however, much higher short-term ethylbenzene concentrations may be encountered during hobby and home maintenance activities. Central tendency and upper bound estimates of personal ethylbenzene exposure concentrations range from about 0.4 to 2.6 ppb, respectively, for non-smokers, and about 1.1 to 5.2 ppb, respectively, for smokers.
Low levels of ethylbenzene occur in foods as a result of partitioning from ambient atmospheric sources or transfer from styrene-based packaging material.
Ethylbenzene does not appear to occur naturally in foods. Its presence in foods is due to partitioning of ambient atmospheric sources of ethylbenzene as well as migration from styrenic food-contact materials. The most current dietary exposure information comes from a 2014 Canadian Diet study which found detections in 91% of food samples tested with average concentrations ranging from 0.04 to 19.25 ppb. The highest concentration reported in this study was in chewing gum (320 ppb) which may have come from the polymer gum base made of styrene-butadiene based synthetic rubber. Styrenic food-contact materials are estimated to contribute 0.42 ppm ethylbenzene concentrations in food. Moderate heating does not result in significant migration of ethylbenzene into packaged foods, but microwaving or other intense heating of food in styrenic (or other plastic) containers can increase migration. The average dietary exposures for children to adults reportedly range from 0.00001 to 0.0001 mg ethylbenzene per kilogram of body weight per day.
The general population is not regularly exposed to measurable levels of ethylbenzene in drinking water.
Although drinking water sources can be affected by localized spills and other releases, studies show that both groundwater and surface water resources used for drinking consistently report low detection frequencies and concentrations of ethylbenzene. Therefore, ethylbenzene intakes via drinking water are negligible for the general public.
Consumer household products or hobby materials that contain petroleum compounds may release ethylbenzene with use.
Consumers may receive inhalation and dermal exposures to ethylbenzene through use of petroleum and mixed xylene products such as spray and liquid paints, paint remover, lacquer/stain/varnish, and joint sealants. Estimated exposures vary widely in accordance with the ethylbenzene concentrations present in the products with exposure models predicting inhalation exposures ranging from 1 ppb to 3 ppm and dermal exposures ranging from 0.002 mg to 1 mg per kilogram of body weight per day. These estimates are based on conservative assumptions.
Presence in Human Tissues
Ethylbenzene is well absorbed by oral and inhalation exposure routes, and because of its widespread presence in the environment, it and/or its metabolites are frequently detected in human tissues.
Large national biomonitoring studies such as the U.S. Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey (NHANES) and the Health Canada’s Canadian Health Measures Study (CHMS) have shown that members of the general population may have concentrations of ethylbenzene in blood in the parts per trillion range. Smoking is associated with higher ethylbenzene concentrations in blood with concentrations about 2.7 times higher in smokers than non-smokers.