CAREX Canada

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CAS No. 75-56-9

Wikipedia, Propylene Oxide^[1]

IARC Monograph Vol. 60, 1994 (Group 2B)

General Information

Propylene oxide (PO) is a flammable colorless liquid with a sweet benzene-like odour.^[2-4] It may also be referred to as epoxy propane or methyloxirane.^[4] There are numerous other synonyms and product names; see HSDB for more information.^[4]

Propylene oxide has been classified by IARC as a group 2B carcinogen, possibly carcinogenic to humans.^[2] There was insufficient evidence available for the IARC Working Group to assess human carcinogenicity.^[2] One case-control study found non-significant increases in lymphatic and hematopoietic cancers following propylene oxide exposure, but no information was given on exposure levels and the study subjects had concurrent exposures to other chemicals.^[2] 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.^[3]

Propylene oxide has been ranked by CAREX Canada as Group B (possible high priority) for both the occupational and environmental settings. Prioritization was based on the carcinogenicity and other toxic properties of the substance, the prevalence of exposure in Canada, and the feasibility of assessing exposure.

Propylene oxide has not been reviewed by IARC since 1994, and more recent exposure and biomarker studies have created renewed interest into furthering the research surrounding PO’s carcinogenicity.^[20]

Regulations and Guidelines

Occupational Exposure Limits (OEL)

Canadian Jurisdictions	OEL (ppm)
Canada Labour Code	2 [sen]
BC, MB, NB, NL, NS, ON, PE	2 [sen]
QC	20
AB	2
SK	2 [sen] 4 [stel]
YT	150 [stel]
NT, NU	20 30 [stel]
Other Jurisdictions	OEL (ppm)
ACGIH 2010 TLV	2 [sen]

ppm = parts per million

stel = short term exposure limit (15 min. maximum)

sen = potential for sensitization

TLV = Threshold Limit Value (8 hour maximum)

Canadian Environmental Guidelines

Jurisdiction	Limit/Designation	Year
Food Additives Permitted for Use	Allowed as a starch-modifying agent	2006^[7]
Maximum Residue Limits on Food	300 ppm for almonds	2010^[18]

Propylene oxide is not included in other Canadian government environmental guidelines reviewed.^[5,6,19]

Canadian Agencies/Organizations

Agency	Designation/Position	Year
Health Canada	DSL – high priority substance with highest potential for exposure	2006^[8]
CEPA (Schedule 1)	Included	2010^[9]
CMP Challenge	Batch 1 [Health]	2008^[10]

DSL = Domestic Substances List

CEPA = Canadian Environmental Protection Act

CMP = Chemicals Management Plan

Main Uses

In Canada, propylene oxide is a chemical intermediate used mainly for the production of polyether polyols, which are used for production of polyurethane foams.^[3,4,12] 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, as well as in the production of unsaturated polyester resins used in the textile and construction industries.^[3,4,12]

Propylene oxide is also used to produce glycol ethers for use in paints and varnishes.^[12]

In Canada, propylene oxide is approved for use in food as a starch-modifying agent and in natural health products as a preservative.^[12] However, Health Canada reported in 2008 that no natural health products contained propylene oxide.^[12] Propylene oxide is not used in cosmetics in Canada.^[12]

In the US, propylene oxide is used in sterilizing food products via fumigation.^[3,12]

PO is not currently registered as a pesticide in Canada (though there are 3 active applications pending at the PMRA)^[21] and food items fumigated with the substance are subject to Health Canada’s Maximum Residue Limits.^[12] This limit is 0.1 ppm,^[12] though this does not apply to almonds, for which there is a higher limit noted above.

Canadian Production and Trade

Propylene oxide is produced via peroxidation and chlorohydrination of propylene.^[12]

In 2007, less than 100 kg of propylene oxide was manufactured in Canada.^[12] Prior to 1993, Dow Chemical Canada in Sarnia, ON produced 60 kilotonnes of propylene oxide annually.^[13]

The majority of domestic demand is met by imports from the United States.^[12]

Production and Trade

Activity	Quantity	Year
Propylene Oxide
Canadian Production	60,000 t	1993^[13]
Domestic Consumption	39,000 t¹	2005^[13]
Polyurethanes
Canadian Production	89,300 t²	1999^[14]
Domestic Consumption	114,900 t²	1999^[14]
Export^*	None	2009^[15]
Import^*: Mainly from the US	4,384 t of ‘propylene oxide'	2009^[15]

1 = forecasted in 2003

2 = forecasted in 1997

t = tonne

Occupational Exposures

Inhalation is the most important route of occupational exposure to propylene oxide.^[3] The main occupations exposed include workers involved in the manufacturing of polyurethane polyols and propylene glycol.^[2,3] Occupational exposure may also occur for workers who use products containing propylene oxide, such as paint strippers.^[3,12]

CAREX Canada is reviewing whether it is feasible to prepare exposure estimates for Canadian workers exposed to propylene oxide. This will likely depend on availability of exposure data.

Environmental Exposures

Propylene oxide does not occur naturally in the environment and is released primarily into the air by industrial sites where it is used and stored.^[12] According to a joint assessment by Health Canada and Environment Canada, propylene oxide is persistent in air but not in water and in soil.^[11] The assessment also found that propylene oxide does not bioaccumulate.^[11]

Other air emission sources include automobile exhaust and other combustion exhaust from stationary sources that burn hydrocarbons.^[12] Based on PO’s usage pattern and limited environmental monitoring information, propylene oxide presence in soil and water is expected to be low.^[11]

Exposure may also occur during the use of consumer products containing propylene oxide, such as automotive products, spray paints and paint strippers.^[3,11]

Exposure to PO in the general public in Canada via foods is expected to be low.^[12] Propylene oxide food additives break down into non-toxic products when combined with water during food production.^[12]

Searches of environmental and consumer product databases yielded the following results on current potential for exposure to propylene oxide in Canada:

NPRI Database

NPRI 2009^[16]
Search Term: propylene oxide
Category	Quantity	Industry
Released into Environment	0.001 t	Chemical manufacture (1 company)
Disposed of	None
Sent to off-site recycling	None