Benzene Environmental Exposures
Benzene Environmental Exposures
CAREX Canada estimates that the primary source of environmental exposure to benzene is indoor air. Benzene is emitted by a number of indoor sources, including glues, paints, furniture wax, and some detergents. Combustion sources such as fireplaces, gas furnaces, cigarette smoke, and vehicles in attached garages may also contribute to indoor concentrations of benzene.
Having an attached garage can lead to increased exposure since benzene can more readily enter the house. For example, in Canada, benzene levels are three times higher in homes with attached garages compared to those with detached or no garages.
The presence of benzene is attributable to engine exhaust, as well as to the evaporation of benzene from gasoline. A recent survey of homes across Canada found indoor concentrations of benzene ranging from 0.10 to 15.19 µg/m3, with average concentrations of 1.93 µg/m3. CAREX Canada’s environmental estimates indicate that benzene levels in indoor and outdoor air may be sources of elevated cancer risk (high data quality).
Outdoor concentrations of benzene are generally lower than indoor concentrations. Major sources of benzene in outdoor air include vehicle combustion of gasoline and diesel fuels, residential fuel combustion, iron and steel production, chemical manufacturing, as well as petroleum and coal products manufacturing.[1,6] Natural sources of benzene in the environment include forest fires, volcanos, petroleum seepage, and emissions from vegetation.
Ambient air benzene levels in different locations in Canada have been monitored since 1989 by the National Air Pollution Surveillance (NAPS) network. A 2012 NAPS update indicated that the concentrations of benzene at 18 urban sites decreased by 74% between 1994 and 2009.
Low levels of benzene are found in some soft drinks and a number of other foods and beverages.[7,8] Benzene contamination in soils and groundwater may also arise from oil and gas spills, underground storage tank leaks, and seepage from waste disposal sites. CAREX Canada’s environmental estimates indicate that benzene levels in food and beverages may be sources of elevated cancer risk (very low data quality), although not in drinking water (moderate data quality).
Searches of Environment Canada’s National Pollutant Release Inventory (NPRI) and the US Household Products Database yielded the following results on current potential for exposure to benzene in Canada:
NPRI and US Household Products Database
|Substance name: ‘Benzene’|
|Released into Environment||736 t||Oil and gas extraction,
basic chemical manufacturing,
iron and steel mills and ferro-alloy manufacturing,
petroleum and coal product manufacturing
|Disposed of||1,065 t|
|Sent to off-site recycling||1,055 t|
t = tonne
|US Household Products 2016|
|Search Term||# Products||Product Type|
|‘Benzene’||17||adhesives (3), interior paints (2), wood finish (1),
adhesive remover (1), pet care lotion (1), sealant (1),
auto part cleaner/degreaser (5), motor oil (3)
This map shows predicted levels of benzene in outdoor air at residential locations by health region in Canada as of 2011. The average (median) concentration of benzene within the health regions measured in outdoor air for 2011 was 0.608 µg/m3, but concentrations of benzene can be higher or lower than average in many locations. Concentrations should be compared to the applicable jurisdictional guidelines and standards for ambient air quality based on chronic, carcinogenic effects (or non-carcinogenic effects, if cancer is not the point of interest).
*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011
Cancer risk estimates
Potential lifetime excess cancer risk (LECR) is an indicator of Canadians’ exposure to known or suspected carcinogens in the environment. When potential LECR is more than 1 per million in a single pathway, a more detailed risk assessment may be useful for confirming the need to reduce individual exposure. If measured levels of benzene in relevant exposure pathways (outdoor air, indoor air, drinking water, and food and beverages) decrease, the risk will also decrease.
Potential LECR is calculated by multiplying lifetime average daily intake (the amount inhaled or ingested) by a cancer potency factor or unit risk factor. More than one cancer potency factor may be available, because agencies interpret the underlying health studies differently, or use a more precautionary approach. Our results use cancer potency factors from Health Canada, the US Environmental Protection Agency (US EPA), and/or the California Office of Environmental Health Hazard Assessment (OEHHA).
The calculated lifetime daily intake and LECR results for benzene are provided in the tables below. For more information on supporting data and sources, click on the Methods and Data tab below.
Calculated lifetime daily intake
Lifetime excess cancer risk (per million people)
*LECR based on average intake x cancer potency factor from each agency
Compare substances: Canadian potential lifetime excess cancer risk, 2011
The data in this table are based on average intake and Health Canada’s cancer potency factor, assuming no change in measured levels. When Health Canada values are not available, United States Environmental Protection Agency values are used.
Click the second tab to view LECR data.
**Exposure not applicable: For indicated pathways, substance not present, not carcinogenic, or exposure is negligible
**Gap in data: No cancer potency factor or unit risk factor, or no data available
IARC Group 1 = Carcinogenic to humans, IARC Group 2A = Probably carcinogenic to humans, IARC Group 2B = Possibly carcinogenic to humans
NOTE: Chromium (hexavalent) estimates assume that 5% of total chromium measured in outdoor air is hexavalent and 8% total chromium measured in indoor dust is hexavalent.
Potential LECR assumes exposure occurs at the same level, 24 hours per day, for 70 years. This is rarely true for any single individual, but using a standard set of assumptions allows us to provide a relative ranking for known and suspected carcinogens across different exposure routes. While ongoing research continually provides new evidence about cancer potency and whether there is a safe threshold of exposure, our approach assumes there are no safe exposure levels.
Methods and Data
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