PAHs
Full Profile
General Information
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.[2-4] Refer to the IARC Monograph for the complete list of chemicals classified under the PAH group.[2]
PAHs occur naturally and generally occur as complex mixtures (i.e. in combustion products).[4] They can also be individually manufactured.[4] Pure PAH chemicals can range from colourless to golden yellow with a faint pleasant odour.[3,4] Most PAHs are insoluble in water.[3]
Different PAHs and occupational exposures associated with PAHs exposure have been classified by IARC into Group 1, 2A, 2B and 3 based on varying strengths of evidence of carcinogenicity in animal and human studies.[2]
Evidence for PAH carcinogenicity in humans is mainly from occupational studies of workers exposed to PAH-containing mixtures. Human cancers associated with exposure to these types of mixtures occur predominantly in the lungs and skin following inhalation and dermal exposure, respectively.[4] Due to the fact that PAHs are often found in complex mixtures, carcinogenic effects of individual PAHs are difficult to assess.[5] Animal studies have shown that a number of pure PAHs are carcinogenic following inhalation, oral and dermal exposure.[4]
A number of different non-cancer adverse health effects associated with PAH exposure have been observed in humans and animals.[4] Depending on the route of exposure, PAH exposure was found to be associated with decrements in lung function, skin inflammation and lesions, and decreases in humoral immunity.[4]
PAHs have been ranked by CAREX Canada as Group A (immediate high priority) for both occupational and environmental settings. Prioritization was based on the carcinogenicity and other toxic properties of the substances, the prevalence of exposure in Canada, and the feasibility of assessing exposure.
IARC Classification of PAHs and related occupational exposures[2]
| IARC Group | Exposure/Substance |
|---|---|
| 1 (Carcinogenic to humans) | Occupational exposure during: Coal gasification Coke production Coal tar distillation Chimney sweeping Paving and roofing with coal tar pitch Aluminum production Substance benzo[a]pyrene |
| 2A (Probably carcinogenic to humans) | Occupational exposure during: Carbon electrode manufacture Substances Creosotes Cyclopenta[cd]pyrene Dibenz[a,h]anthracene Dibenzo[a,l]pyrene |
| 2B (Possibly carcinogenic to humans) | Substances 5-methylchrysene benz[j]aceanthrylene benz[a]anthracene benzo[b]fluoranthene benzo[j]fluoranthene benzo[k]fluoranthene benzo[c]phenanthrene Chyrsene dibenzo[a,h]pyrene dibenzo[a,i]pyrene indeno[1,2,3-cd]pyrene |
| 3 (Not classifiable re: carcinogenicity to humans) | All other PAHs |
Regulations and Guidelines
Occupational Exposure Limits (OEL)
| Canadian Jurisdictions | OEL (mg/m3) |
|---|---|
| Canada Labour Code | BEI suggested (no level given) |
| SK | 0.2 [PPAH] [ds] 0.6 [stel] |
| QC | 0.2 [EM] (volatile coal tar pitch) |
NT, NU | 0.2 [PPAH] 0.6 [stel] |
MB, NL, PE, NS | BEI suggested (no level given) |
BC, AB, ON, NB, YT | None listed |
| Other Jurisdictions | OEL (mg/m3) |
| ACGIH 2010 TLV | BEI suggested (no level given) |
Canadian Environmental Guidelines
| Jurisdiction | Limit (mg/L) | Year |
|---|---|---|
| Canadian Drinking Water Guidelines | Benzo[a]pyrene 0.00001 mg/L (MAC) |
2010[6] |
| Residential Indoor Air Quality |
Exposures to PAHs should be kept to a minimum by:
|
1987[7] |
Canadian Agencies/Organizations
| Agency | Designation/Position | Year |
|---|---|---|
| Health Canada |
Benzo[a]pyrene: low priority substance (already risk managed)
Creosote & Chrysene: high priority substance with low potential for exposure
| 2011[10] |
| CEPA | Schedule 1, paragraphs ‘a’ and ‘c’ |
2011[11] |
Main Uses
PAHs are primarily by-products of incomplete combustion and petroleum product production and processing. Most pure PAHs are not used in commercial production or processes except for use in various research laboratories.[3,4]
Some pure PAHs, such as anthracene and acenphthene, are used as in dye production and in the manufacturing of pharmaceuticals.[4]
PAHs are present in coal tar and other products derived from coal tar such as coal tar pitch, creosote, bitumen and asphalt.[3] 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.[3]
Canadian Production and Trade
No quantitative Canadian commercial production and trade information was found for PAH as a group in Camford Information Services or TradeMap.[13,14]
Occupational Exposures
Inhalation and dermal exposure are main routes of exposure to PAHs in occupational settings.[4]
Highly exposed occupations include 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, metal working, calcium carbide production, municipal trash incinerators, petroleum industries, chemical production and transportation, electrical industries and chimney sweeping.[2,4]
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.[2]
Environmental Exposures
Environmental exposure to PAHs primarily occur through the inhalation of tobacco smoke, wood fire smoke, and contaminated air as well as ingestion of contaminated water and various foods. Dermal exposure upon contact with creosote treated wood, soot or tar could also occur.[2,3]
In Canada, forest fires are the greatest natural source of PAHs in the environment, releasing approximately 2000 tonnes of PAHs every year (47% of total atmospheric emissions). However, because forest fires occur at different times and in different locations, high exposures are not occurring in any specific area or population.[5] Other natural sources of PAHs include volcanoes, crude oil, and shale oil.[4]
According to a 1994 Canadian government report, the largest anthropogenic source of atmospheric PAHs was aluminum smelting, releasing 925 tonnes of PAHs per year.[5] Other significant human sources of PAHs release into the air include residential wood heating (474 t/yr); agricultural burning and open fires (358 t/yr); the incineration of wood waste by saw mills (249 t/yr); and transportation (201 t/yr).[5]
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.[5] Urban concentrations of background PAHs were consistently higher than rural areas in both US and Canada.[4,5]
PAHs are found in smoked, barbequed, deep fried and charcoal-broiled foods, cereals and grains, meats, and vegetables (particularly those grown in contaminated areas).[3,4]
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.[4,5]
One study estimated that, for a typical American male, exposures to carcinogenic PAHs through inhalation of ambient air, ingestion of food and ingestion of drinking water ranged from 0.02-3 μg/day, 1-9 μg/day, and 0.0002-0.12 μg/day, respectively.[15]
A search of the National Pollutant Release Inventory (NPRI) yielded the following results on current environmental release of PAHs in Canada:
| NPRI 2009 [16] | ||
|---|---|---|
| Search Term: Results: |
'PAHs, total unspeciated' 21 companies |
|
| Category | Quantity | Industry |
| Released into environment | 2,419 t (air: 2,410) |
Mining, manufacturing, pulp and paper industries. |
| Disposed of | 138 t | |
| Sent to off-site recycling | 2.1 t | |
Sources
- Wikipedia Commons (2011)
- IARC (2006) Monograph, Volume 92
- US Department of Health and Human Services (2005) NTP 12th report on carcinogens for Polycylic Acomatic Hydrocarbons (PAHs) – 15 Listings
- ATSDR (1995) Toxicological Profile for Polycyclic Aromatic Hydrocarbons (PAH)
- Priority Substances List assessment report (CEPA) for Polycyclic Aromatic Hydrocarbons (1994)
- Health Canada (2010) Guidelines for Canadian Drinking Water
- Health Canada (1987) Exposure Guidelines for Residential Indoor Air Quality
- Health Canada (2006) Categorization of the Domestic Substances List under CEPA
- Environment Canada (2010) Toxic Substances List – CEPA Schedule 1
- CCOHS (2011) MSDS database
- Industry Canada (2011) Canadian Company Capabilities
- ChemSources (2011) Database for international chemical suppliers (free subscription required)
- Camford Information Services (2005) CPI Product Profiles
- TradeMap (2011) Canadian international trade (free subscription required)
- Menzie et al. (1992) Ambient concentrations and exposure to carcinogenic PAHs in the environment. Environ Sci Technol 26(7):1278-1284.
- Environment Canada (2009) The National Pollutant Release Inventory
