PAHs Environmental Exposures
PAHs Environmental Exposures
Overview
Environmental exposure to PAHs primarily occur through inhaling tobacco smoke, wood fire smoke, and contaminated air, as well as ingesting contaminated water and various foods. Dermal exposure upon contact with creosote treated wood, soot, or tar can also
occur.[1,2]
Environmental estimates are available for the following PAHs:
- Benzo[a]pyrene
- Benz[a]athracene
- Benzo[b]fluoranthene
- Benzo[k]fluoranthene
- Chrysene
- Indeno[1,2,3-cd]pyrene
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In 1990, forest fires were the greatest natural source of PAHs in the environment in Canada, releasing approximately 47% of total atmospheric emissions.[3] Current data on the amount of PAHs released due to wildfires could not be located. However, the severity of wildfires is expected to increase with climate change, and thus wildfires are likely to remain an important source of PAHs.[4] Other natural sources of PAHs include volcanoes, crude oil, and shale oil.[5]
The Air Pollution Emissions Inventory (APEI) of Environment Canada reports emissions for four PAHs, allowing for analysis of general trends in PAHs.[6] Since the 1990s, PAH emissions have decreased by 61%, most likely due to emission reductions in the aluminum industries and iron and steel industries. The APEI reported that in 2014, 130 tonnes of PAHs were emitted in Canada (excluding natural sources). The majority of emissions (78%) were due to residential fuel wood combustion. Industrial sources accounted for 18% of emissions, which were mostly due to the aluminum industry.[6]
Median ambient concentrations of PAHs in Canadian communities ranged from 7.2 ng/m3 in rural areas to 693 ng/m3 in areas near aluminum smelters.[3] Urban concentrations of background PAHs were consistently higher than rural areas in both US and Canada.[3,5]
PAHs are found in smoked, barbequed, deep fried, and charcoal-broiled foods, cereals and grains, meats, and vegetables (particularly those grown in contaminated areas).[2,5] In the general population, food sources can contribute up to 70% of PAH exposure in nonsmokers.[7]
Detectable levels of PAHs were found in surface water, groundwater, and drinking water in Canada, although levels are typically low as PAHs are insoluble in water.[3,5]
A search of Environment Canada’s National Pollutant Release Inventory (NPRI) yielded the following results on current potential for exposure to PAHs in Canada:
| NPRI 2014 [8] | ||
|---|---|---|
| Search Term: Results: | ‘PAHs, total unspeciated’ | |
| Category | Quantity | Industry |
| Released into environment | 3,712 t (air: 3,315) | Mining, manufacturing, pulp and paper industries (59 facilities) |
| Disposed of | 831.5 t | |
| Sent to off-site recycling | 547.3 t | |
t = tonne
Mapping
The maps below shows predicted levels of six PAHs in outdoor air at residential locations in Canada in 2011. 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).
Benzo[a]pyrene
Predicted annual average benzo[a]pyrene concentrations in outdoor air at residential locations by health region, 2011
*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011
Benz[a]anthracene
The average (median) concentration of benz[a]anthracene within the health regions measured in outdoor air for 2011 was 0.00021 µg/m3, but concentrations of benz[a]anthracene can be higher or lower than average in many locations.
Predicted annual average benz[a]anthracene concentrations in outdoor air at residential locations by health region, 2011
*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011
Benzo[b]fluoranthene
The average (median) concentration of benzo[b]fluoranthene within the health regions measured in outdoor air for 2011 was 0.0006 µg/m3, but concentrations of benzo[b]fluoranthene can be higher or lower than average in many locations.
Predicted annual average benzo[b]fluoranthene concentrations in outdoor air at residential locations by health region, 2011
*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011
Benzo[k]fluoranthene
The average (median) concentration of benzo[k]fluoranthene within the health regions measured in outdoor air for 2011 was 0.00015 µg/m3, but concentrations of benzo[k]fluoranthene can be higher or lower than average in many locations.
Predicted annual average benzo[k]fluoranthene concentrations in outdoor air at residential locations by health region, 2011
*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011
Chrysene
The average (median) concentration of chrysene within the health regions measured in outdoor air for 2011 was 0.00035 µg/m3, but concentrations of chrysene can be higher or lower than average in many locations.
Predicted annual average chrysene concentrations in outdoor air at residential locations by health region, 2011
*Measured at the National Air Pollution Surveillance (NAPS) monitors in 2011
Indeno[1,2,3-cd]pyrene
Predicted annual average indeno(1,2,3-cd)pyrene concentrations in outdoor air at residential locations by health region, 2011
*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 PAHs in relevant exposure pathways (outdoor air, indoor air, indoor dust, 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).
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.
The calculated lifetime daily intake and LECR results for six PAHs are provided below. For more information on supporting data and sources, click on the Methods and Data tab below.
Benzo[a]pyrene
Calculated Lifetime Daily Intake – Benzo[a]pyrene
Lifetime Excess Cancer Risk (per million people) – Benzo[a]pyrene
*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.
Benz[a]anthracene
Calculated Lifetime Daily Intake – Benz[a]anthracene
Lifetime Excess Cancer Risk (per million people) – Benz[a]anthracene
*LECR based on average intake x cancer potency factor from each agency
Benzo[b]fluoranthene
Calculated Lifetime Daily Intake – Benzo[b]fluoranthene
Lifetime Excess Cancer Risk (per million people) – Benzo[b]fluoranthene
*LECR based on average intake x cancer potency factor from each agency
Benzo[k]fluoranthene
Calculated Lifetime Daily Intake – Benzo[k]fluoranthene
Lifetime Excess Cancer Risk (per million people) – Benzo[k]fluoranthene
*LECR based on average intake x cancer potency factor from each agency
Chrysene
Calculated Lifetime Daily Intake – Chrysene
Lifetime Excess Cancer Risk (per million people) – Chrysene
*LECR based on average intake x cancer potency factor from each agency
Indeno[1,2,3-cd]pyrene
Calculated Lifetime Daily Intake – Indeno[1,2,3-cd]pyrene
Lifetime Excess Cancer Risk (per million people) – Indeno[1,2,3-cd]pyrene
*LECR based on average intake x cancer potency factor from each agency
Methods and Data
Our Environmental Approach page outlines the general approach used to calculate lifetime excess cancer risk estimates and includes documentation on our mapping methods.
Data sources and data quality can be found in the PDFs below.
Supplemental data – Benzo[a]pyrene [PDF]
Supplemental data – Benz[a]athracene [PDF]
Supplemental data – Benzo[b]fluoranthene [PDF]
Supplemental data – Benzo[k]fluoranthene [PDF]
Sources
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