OTHERS – MULTIPLE CLASSIFICATIONS (IARC 1, 2A, 2B, 3)
- A group of over 100 chemicals formed during the incomplete burning of coal, oil, gas, wood, garbage, and other organic substances
- Associated cancers: Lung and skin cancers, plus others with limited evidence
- Most important route of exposure: Inhalation, skin contact
- Primary source: By-products of incomplete combustion (ex. coal, oil, gas, wood, garbage, and other organic substances such as tobacco and charbroiled meat) and petroleum production and processing
- Occupational exposures: Approx. 467,000 Canadians are exposed to PAHs at work, primarily in restaurants, automotive repair and maintenance, and gasoline stations
- Environmental exposures: Via tobacco smoke, wood fire smoke, and contaminated air, water, and food
- Fast fact: PAHs are found in smoked, barbequed, deep fried, and charcoal-broiled foods, cereals and grains, meats, and vegetables.
Polycyclic aromatic hydrocarbons (PAHs) are a group of over 100 chemicals formed during the incomplete burning of coal, oil, gas, wood, garbage, and other organic substances such as tobacco and charbroiled meat.[1,2,3] Refer to the International Agency for Research on Cancer (IARC) Monograph for the complete list of chemicals classified under the PAH group.
PAHs occur naturally and generally exist as complex mixtures (i.e. in combustion products). They can also be individually manufactured. Pure PAH chemicals can range from colourless to golden yellow in colour, with a faint and pleasant odour.[2,3] Most PAHs are insoluble in water.
Different PAHs have been classified by IARC into Group 1, 2A, 2B, and 3 based on varying strengths in the evidence of carcinogenicity in animal and human studies. Evidence for PAH carcinogenicity in humans mainly stems from studies of workers exposed to PAH-containing mixtures. Human cancers associated with these mixtures occur predominantly in the lungs and skin following inhalation and dermal exposure, respectively. Because PAHs are often found in complex mixtures, carcinogenic effects of individual PAHs are difficult to assess. Animal studies show that a number of pure PAHs are carcinogenic.
Occupational exposures that are associated with PAHS have been classified by IARC into Group 1 and 2A.[1,5] Similar to the various PAHs that have been assessed by IARC, these occupational exposures have been linked to cancers of the lung and skin in humans. Occupational exposure during aluminum production has also been classified as a definite cause of bladder cancer; this association may be due to PAH exposures, although it is difficult to tease apart the effects of PAHs from other carcinogenic exposures during aluminum production.
Other adverse health effects associated with PAH exposure have been observed in humans and animals. Depending on the route of exposure, PAH exposure was associated with decrements in lung function, skin inflammation and lesions, and decreases in immunity.
IARC Classification of PAHs and related occupational exposures
|1 (Carcinogenic to humans)||Occupational exposure during:
Coal tar distillation
Paving and roofing with coal tar pitch
|2A (Probably carcinogenic to humans)||Occupational exposure during:
Carbon electrode manufacture
|2B (Possibly carcinogenic to humans)||Substances
|3 (Not classifiable re: carcinogenicity to humans)||All other PAHs|
Regulations and Guidelines
|Canadian Jurisdictions||OEL (mg/m3)|
|Canada Labour Code||0.2*|
|AB, BC, MB, NB, NL, NS, ON, PE||0.2*|
|NT, NU, SK||0.2*
|Other Jurisdictions||OEL (mg/m3)|
|ACGIH 2020 TLV||0.2*|
* for coal tar pitch volatiles as benzene soluble aerosol
mg/m3 = milligrams per cubic meter
stel = short term exposure limit (15 min. maximum)
em = exposure must be reduced to the minimum
ACGIH = American Conference of Governmental Industrial Hygienists
TLV = threshold limit value
Canadian environmental guidelines and standards*
|Canadian Drinking Water Guidelines||Benzo[a]pyrene: 0.004 µg/L (MAC)||2016|
|BC Drinking Water Guidelines||All PAHs: 0.004 µg/L (MAC)||2020|
|Other Drinking Water Guidelines (MB) and Standards (ON, SK)||Benzo[a]pyrene: 0.01 µg/L (MAC)||2003-2020
|Residential Indoor Air Quality||
Exposures to PAHs should be kept to a minimum by:
|Alberta Ambient Air Quality Objectives and Guidelines||Benzo[a]pyrene: Annual: 0.30 ng/m3||2009|
|Ontario Ambient Air Quality Criteria||Benzo[a]pyrene as a surrogate of total PAHs
Annual: 0.01 ng/m3
24-hour: 0.05 ng/m3
|Ontario’s Air Pollution – Local Air Quality Regulation||Annual: 0.01 ng/m3; Prohibited discharge into the air if the concentration of PAHs exceeds the standard||2020|
|List of Maximum Levels for Various Chemical Contaminants in Foods||3 µg/kg Benzo[a]pyrene Toxic Equivalents in olive-pomace oils (this is a unique type of oil, distinct from other olive oils such as virgin olive oil)||2020|
|BC Contaminated Sites Regulation||For benzo[a]pyrene:
Sets soil standards for the protection of human health:
Agricultural and low density residential sites: 5 μg/g
Urban park and high density residential sites: 10 μg/g
Commercial sites: 30 μg/g
Industrial sites: 50 μg/g
Drinking water: 0.01 µg/L
MAC = maximum allowable concentration
mg/L = milligrams per litre
ng/m3 = nanograms per cubic metre
µg/g = micrograms per gram
*Standards are legislated and legally enforceable, while guidelines (including Ontario ambient air quality criteria) describe concentrations of contaminants in the environment (e.g. air, water) that are protective against adverse health, environmental, or aesthetic (e.g. odour) effects
Benzo[a]pyrene: DSL – low priority substance (already risk managed)
Creosote & Chrysene: DSL – high priority substance with low potential for exposure
|CEPA||Schedule 1, paragraphs ‘a’ and ‘c’||1999|
|Environment Canada’s National Pollutant Release Inventory||Reportable to NPRI if released, disposed of, or transferred for recycling at quantities greater than: 50 kg total PAHs||2016|
|National Classification System for Contaminated Sites||Rank: “Medium to high hazard” (variable based on compound)||2008|
|Canada-Ontario Agreement on Great Lakes Water Quality and Ecosystem Health||Tier 1 chemical: targeted for virtual elimination (benzo-a-pyrene)
Tier 2 chemical: potential for causing widespread impacts, or that have already caused local adverse impacts on the Great Lakes Basin Ecosystem (17 PAHs)
DSL = domestic substance list
CEPA = Canadian Environmental Protection Act
PAHs were not included in other Canadian government guidelines, standards, or chemical listings reviewed.
PAHs are primarily by-products of incomplete combustion and petroleum product production and processing. Most pure PAHs are not used for commercial purposes, with the exception of applications in research laboratories.[3,2]
Some pure PAHs, such as anthracene and acenaphthene, are used to produce dyes and manufacture pharmaceuticals.
PAHs are present in coal tar and other products derived from coal tar, such as coal tar pitch, creosote, bitumen, and asphalt. Coal tar and associated coal tar products may be used as a fuel, in road and roof paving, in carbon electrode manufacturing and in wood preservation. CAREX Canada has developed carcinogen profiles for many of these products; visit our Profiles and Estimates page to view.
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
In 1990, forest fires were the greatest natural source of PAHs in the environment in Canada, releasing approximately 47% of total atmospheric emissions. 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. Other natural sources of PAHs include volcanoes, crude oil, and shale oil.
The Air Pollution Emissions Inventory (APEI) of Environment Canada reports emissions for four PAHs, allowing for analysis of general trends in PAHs. 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.
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. Urban concentrations of background PAHs were consistently higher than rural areas in both US and Canada.[2,4]
PAHs are found in smoked, barbequed, deep fried, and charcoal-broiled foods, cereals and grains, meats, and vegetables (particularly those grown in contaminated areas).[3,2] In the general population, food sources can contribute up to 70% of PAH exposure in nonsmokers.
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 |
|Search Term: ‘PAHs, total unspeciated’|
|Released into environment||3,712 t
|Mining, manufacturing, pulp and paper industries (59 facilities)|
|Disposed of||831.5 t|
|Sent to off-site recycling||547.3 t|
t = tonne
For more information, see the environmental exposure estimate page for PAHs.
Inhalation and dermal exposure are the main routes of exposure to PAHs in occupational settings.
CAREX Canada estimates that approximately 467,000 Canadians are exposed to PAHs in their workplaces. The largest industrial groups exposed are restaurants, automotive repair and maintenance, and gasoline stations.
The largest occupational groups exposed to PAHs are cooks, where PAHs are released in the kitchen while food is being cooked. Other food establishment workers may also be exposed, including chefs. Automative service technicians and mechanics and firefighters may be exposed as well, along with workers in coal tar production and distillation, coal gasification, coke production, paving and roofing using coal tar, creosote wood preservation, aluminum production, carbon electrode manufacture, mining, metalworking, calcium carbide production, municipal trash incinerators, petroleum industries, chemical production and transportation, electrical industries, and chimney
In some industries, such as aluminum production, benzo[a]pyrene levels can reach up to 100 µg/m3, which is more than 10,000 times higher than typical ambient air concentrations.
According to the Burden of Occupational Cancer in Canada project, occupational exposure to PAHs leads to approximately 130 lung cancers, 50 skin cancers, and possibly 80 suspected bladder cancers each year in Canada, based on past exposures (1961-2001).[41,42] This amounts to 0.6% of all lung cancers, 0.1% of all skin cancers, and 1% of all bladder cancers diagnosed annually. Most PAH-related cancers occur among workers in the manufacturing and construction sectors. Work-related PAH exposure resulted in approximately $183 million in costs for newly diagnosed lung, non-melanoma skin, and suspected bladder cancer cases in 2011.
For detailed estimates of exposure to PAHs, see the occupational exposures tab.
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