Industrial Chemicals– Possible Carcinogen (IARC 2B)
CAS No. 75-56-9
Photo: Wikimedia Commons
IARC Monograph Vol. 60, 1994 (Group 2B)
Propylene oxide is a flammable, colorless liquid with a sweet, benzene-like odour.[2,3,4] It may also be referred to as epoxy propane or methyloxirane. There are numerous other synonyms and product names; see the Hazardous Substances Data Bank (HSDB) for more information.
Propylene oxide has been classified by the International Agency for Research on Cancer (IARC) as Group 2B, possibly carcinogenic to humans. There was insufficient evidence available for the IARC Working Group to assess human carcinogenicity. One case-control study found non-significant increases in lymphatic and hematopoietic cancers following exposure to propylene oxide. However, no information was given on exposure levels and the study subjects had concurrent exposures to other chemicals. In experimental rats and mice, depending on the method of administration, propylene oxide caused increased incidence of forestomach, nasal, thyroid, adrenal gland, peritoneum, mammary gland, and skin cancers.
Propylene oxide has not been reviewed by IARC since 1994, and more recent exposure and biomarker studies have renewed interest into further investigation of its carcinogenicity.
Propylene oxide is not included in other Canadian environmental guidelines reviewed.[12,13,14,15,16]
DSL - high priority substance with highest potential for exposure
CEPA (Schedule 1)
Batch 1 [Health]
DSL = Domestic Substances List
CEPA = Canadian Environmental Protection Act
CMP = Chemicals Management Plan
Propylene oxide was not found in any other Canadian chemical listings reviewed.[20,21]
In Canada, propylene oxide is a chemical intermediate used mainly to produce polyether polyols, which are then used to produce polyurethane foams.[3,4,22] Propylene oxide is also used to produce glycol ethers for use in paints and varnishes. Propylene glycols are also manufactured from propylene oxide. Propylene glycols are used in a variety of products including resins, pharmaceuticals, food moisteners, inks, synthetic lubricants, solvents, additives in motor fuels, lubricants, and cleaners. They are also used to produce unsaturated polyester resins used in the textile and construction industries.[3,4,22]
Propylene oxide is approved for use in food as a starch-modifying agent and in natural health products as a preservative in Canada. However, Health Canada reported in 2008 that no natural health products contained propylene oxide. Propylene oxide is not used in cosmetics in Canada. It is also not currently registered as a pesticide in Canada.
In the US, propylene oxide is used to sterilize food products via fumigation.[3,22] In Canada, food items fumigated with propylene oxide are subject to Health Canada's Maximum Residue Limits. This limit is 0.1 ppm, though this does not apply to almonds, for which there is a higher limit noted in the Canadian Environmental Guidelines table above.
Canadian Production and Trade
Propylene oxide is produced via peroxidation and chlorohydrination of propylene. The majority of domestic demand is met by imports from the United States.
Production and Trade
t = tonne
Inhalation is the most important route of occupational exposure to propylene oxide.
The main occupations exposed to include workers involved in manufacturing polyurethane polyols and propylene glycol.[2,3] Occupational exposure may also occur in workers who use products containing propylene oxide, such as paint strippers.[3,22]
CAREX Canada has not prioritized Propylene Oxide for exposure estimate development. This is because there is a lack of exposure monitoring data in the Canadian Workplace Exposure Database on which to base an estimate.
Propylene oxide does not occur naturally in the environment. It is released primarily into the air by industrial sites where it is used and stored. According to a joint assessment by Health Canada and Environment Canada, propylene oxide is persistent in air but not in water and in soil. The assessment also found that propylene oxide does not bioaccumulate.
Other air emission sources include automobile exhaust and other combustion exhaust from stationary sources that burn hydrocarbons. Based on propylene oxide usage patterns and limited environmental monitoring information, propylene oxide presence in soil and water is expected to be low.
Exposure may also occur when using consumer products that contain propylene oxide, such as automotive products, spray paints, and paint strippers.[3,25]
Exposure to propylene oxide in the general public in Canada via foods is expected to be low. Propylene oxide food additives break down into non-toxic products when combined with water during food production. Health Canada conducts surveillance of propylene oxide in foods through the Food Safety Action Plan (FSAP). Propylene oxide was not detected in any of the 1,064 samples collected for analysis between 2009-2011.
Propylene oxide releases to the environment are reportable to the National Pollutant Release Inventory (NPRI) in Canada. A total of 0.004 t was recorded for on-site releases in 2015. A search of the US Household Products Database for propylene oxide yielded the following results:
Our team has performed a detailed scan of exposure control resources and assembled a compilation of key publications and resources. These are organized by type of exposure (environmental or occupational) and by specificity (general or carcinogen-specific). Please visit our Exposures Reduction Resources page to view.
We also recommend exploring the Prevention Policies Directory, a freely-accessible online tool offering information on policies related to cancer and chronic disease prevention. Providing summaries of the policies and direct access to the policy documents, the Directory allows users to search by carcinogen, risk factor, jurisdiction, geographical location, and document type. Click here to learn more about policies specific to propylene oxide in the Directory. For questions about this resource, please contact a member of the Prevention Team at the Canadian Partnership Against Cancer at firstname.lastname@example.org.