Styrene and Styrene-7,8-Oxide
Full Profile
General Information
Both styrene and styrene-7,8-oxide are sweet-smelling liquids that appear colourless or yellow in colour.[2] Produced since the 1920’s, styrene is one of the most important monomers worldwide.[3] Styrene-7,8-oxide is a major metabolite of styrene in humans as well as an industrial chemical.[3,4] Styrene may also be referred to as vinylbenzene or ethenylbenzene.[2] Styrene-7,8-oxide may be referred to as phenyloxirane or styrene oxide.[2,5] There are numerous other synonyms and product names for both styrene and styrene-7,8-oside; see HSDB for more information.[5]
Styrene has been classified by IARC as a Group 2B carcinogen, possibly carcinogenic to humans, based on limited evidence in animals and humans.[4] Styrene caused lung tumours in one inhalation study in mice, but other studies did not provide reliable evidence on carcinogenicity. In occupational studies, exposure to styrene has been linked to the development of lymphatic and hematopoietic cancers, but the excess risk is generally small and statistically unstable.[4]
Styrene-7,8-oxide has been classified by IARC as a Group 2A carcinogen, probably carcinogenic to humans, based on animal and mechanistic evidence.[3] Styrene-7,8-oxide caused forestomach cancer in rats and mice, as well as liver tumours in male mice.[3] There has been speculation that styrene-7,8-oxide is the cause of the positive results in the study of styrene exposure and lung tumours in mice.[4]
In addition, styrene exposure can lead to central and peripheral nervous system effects, decreased colour discrimination (reversible), and hearing problems.[4] It can also cause eye and throat irritation, dermatitis, and a syndrome called ‘styrene sickness’ characterized by feelings of unsteadiness, headache, weakness, and decreased nerve conduction.[5] Styrene-7,8-oxide exposure causes skin irritation and sensitization.[5]
How did CAREX choose this agent for review?
Regulations and Guidelines
Occupational Exposure Limits (OEL)
| Styrene | |
|---|---|
| Canadian Jurisdictions | OEL (ppm) |
| Canada Labour Code | 20 [bei] 40 [stel] |
| BC | 50 75 [stel] |
| NT, NU | 50 100 [stel] |
| AB, SK | 20 40 [stel] |
| MB, NL, PE, NB, NS | 20 [bei] 40 [stel] |
| ON | 35 100 [stel] |
| QC | 50 [sk] 100 [stel] |
| YT | 100 125 [stel] |
| Other Jurisdictions | OEL (ppm) |
| ACGIH 2010 TLV | 20 [bei] 40 [stel] |
Canadian Environmental Guidelines
Styrene and styrene-7,8-oxide are not included in Canadian environmental guidelines reviewed.[6,7,23,24]
Canadian Agencies/Organizations
Styrene is included in Health Canada’s Domestic Substance List (DSL) as a low priority substance with risks already managed.[8] Styrene and styrene-7,8-oxide were not found in any other Canadian chemical listings reviewed.[9,25]
Main Uses
Styrene is used primarily in the manufacture of:[4]
- Polystyrene resins for plastic packaging, disposable cups, containers, and insulation.
- Co-polymers with acrylonitrile and/or 1,3-butadiene for synthetic rubber and latex (usually referred to as ABS – acrylonitrile, butadiene, styrene).
- These products may then be used in the manufacture of pipes, automobile parts, food containers, and carpet backing.[2]
In Canada, styrene is used mainly in the production of polystyrene.[10] Polystyrene is purchased by many Canadian companies for use in foam insulation, custom mouldings, cups, flower pots, plastic toys and films, and packaging.[11]
Five companies in Canada (1 in Ontario, 3 in Quebec, and 1 in Alberta) used styrene to produce over 200,000 tonnes of polystyrene in 2006.[11]
Styrene is also used in the production of styrene-butadiene (SB) latex by one company in Canada,[12] and for SB rubber by another company.[13] SB rubber is primarily used in tire manufacture, while SB latex is used in the foam underlay of carpets and as a paper coating.
An additional use for styrene is in the production of glass-reinforced plastics.[10]
Styrene-7,8-oxide is used as a chemical intermediate in the production of styrene glycol, cosmetics, surface coatings, treatment of fibres and textiles, as well as agricultural and biological chemicals.[5,26] It is also used in the production of epoxy resins and an ingredient for the perfume chemical 2-phenylethanol.[5,26]
Canadian Production and Trade
As of 2006, there were 2 main manufacturers of styrene monomer in Canada (one in Ontario and one in Alberta).[14]
Production and Trade
| Activity | Quantity | Year | |
|---|---|---|---|
| Domestic Production | 718 kt/year (~490 exported) | 1990[10] | |
| Domestic Production | 700 kt/year (~470 exported) | 1993[10] | |
| Domestic Production | 789 kt | 2003[14] | |
| Domestic Production | 811 kt (forecasted) | 2006[14] | |
| Domestic Demand | 256 kt (forecasted) | 2006[14] | |
| Export: Mainly to US | 655 kt of ‘styrene’ | 2010[17] | |
| Export: Mainly to US | 49 kt ‘polymers of styrene’ | 2010[17] | |
| Import: Mainly from the US | 5.4 kt of ‘styrene' | 2010[17] | |
| Import: Mainly from US, Korea | 239 kt of ‘polymers of styrene’ | 2010[17] | |
Occupational Exposures
Inhalation is the most important route of occupational exposure for styrene.[2]
Workers can be exposed to styrene during the manufacture and use of styrene, and the manufacture of polystyrene, SB rubber, ABS resins, and glass-reinforced plastic.[2] Exposure levels are highest for workers in the reinforced plastics industry (generally <100 ppm, but much higher levels have been reported). Reinforced plastics are used in the fabrication of boats, automobile parts, shower stalls, tanks and tubs.[2] In other common styrene exposure scenarios, exposure levels are rarely reported above 20 ppm.[2]
Occupational exposure to styrene-7,8-oxide is primarily due indirect exposure to styrene because styrene is primarily metabolized via the styrene-7,8-oxide pathway in humans.[3,4] Styrene-7,8-oxide is also formed when styrene reacts with oxygen in air, or with other oxidizing agents in industrial processes.[3,25] In Finnish plastic plants where polyester resins with styrene were used with peroxide, air styrene-7,8-oxide concentrations were linked to styrene concentrations at a ratio of approximately 1:1000.[3] Direct occupational exposure to styrene-7,8-oxide may also occur in workers in rubber product and paint manufacturing.[25]
CAREX Canada has prepared estimates for the number of Canadian workers exposed to styrene. CAREX Canada is reviewing whether it is feasible to prepare separate exposure estimates for Canadian workers exposed to styrene-7,8-oxide.
Environmental Exposures
The general population is most commonly exposed to styrene via indoor air.[2] Styrene can enter the air from industrial releases, vehicle exhaust, incineration emissions and tobacco smoke.[2,4,17]
Environmental exposure to styrene-7,8-oxide may occur via the inhalation of contaminated air and the consumption of contaminated water and foods.[25] However, general public exposure is expected to be low as environmental releases of styrene-7,8-oxide from industrial sites are low both in Canada and the US.[21,25]
Low levels of naturally-occurring styrene have been found in a number of foods including fruits, vegetables, nuts, beverages, and meats.[18] Small amounts of styrene and styrene-7,8-oxide may also migrate to different foods from styrene-based plastic food packaging.[10,18,26] Typical amount of styrene migration from packaging into food is in the range of 5-30 ppb.[18] One UK study estimated that the migration of styrene-7,8-oxide into food is in the range of 0.002-0.15 ppb.[26]
Styrene-Butadiene rubber is allowed as a chewing gum base in the US.[19] In Canada, styrene is not listed as an allowed food additive or flavouring preparation.[20] Regulations in Canada do not require the ingredients of chewing gum base to be made available.
In 1993, the estimated daily intake for the non-smoking general population in Canada ranged from <0.20 to <0.79 micrograms/kilogram of body weight (depending on age).[10] Cigarette smoke added an extra 2.86 – 3.51 micrograms of styrene/kilogram of body weight per day.[10]
Environmental releases of styrene oxide are reportable to Environment Canada’s National Pollutant Release Inventory. However, no releases were reported from 1999-2009.[21]
Searches of environmental and consumer product databases yielded the following results on current potential for exposure to styrene in Canada:
NPRI Database
| NPRI 2009[21] | |
|---|---|
| Search Term: | ’styrene’ |
| Results: | 117 companies |
| Category | Quantity | Industry |
|---|---|---|
| Released into Environment | 1,253 t | Plastic product manufacturers, polystrene foam production and resin and coatings manufacturers |
| Disposed of | 64 t | |
| Sent to off-site recycling | 38 t |
| US Household Products 20011[22] | ||
|---|---|---|
| Result: 1 product | ||
| Search Term | Quantity | Product Type |
| ’styrene oxide' | 11 | Paints, adhesives, wood fillers, and stain sealers |
| ’styrene oxide' | 0 | |
Sources
- Wikimedia Commons (2007) Photo: Styrene
- US Department of Health and Human Services (2008) NTP: Final Report on Carcinogens, Background Document for Styrene
- IARC (1994) Monograph, Volume 60
- IARC (2002) Monograph Summary, Volume 82
- US National Library of Medicine (2011) Hazardous Substances Data Bank entry for styrene (Search term: ‘styrene’)
- 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
- Government of Canada, Environment Canada & Health Canada (1993) Priority Substances List Assessment Report Styrene
- Camford Information Services (2004) CPI Product Profile: Polystyrene
- Camford Information Services (1999) CPI Product Profile: Styrene-butadiene latex
- Camford Information Services (1999) CPI Product Profile: Styrene-butadiene rubber
- Camford Information Services (2004) CPI Product Profile: Styrene
- ChemSources (2011) Database for international chemical suppliers (free subscription required)
- Industry Canada (2011) Canadian Company Capabilities
- TradeMap (2010) Canadian International Trade (free subscription required)
- ATSDR (2007) Toxicological Profile for Styrene
- US Food and Drug Administration (2006) Food Additive Status List
- Canada Department of Justice (2011) Food and Drug Regulations
- Environment Canada (2009) The National Pollutant Release Inventory
- US Department of Health and Human Services (2011) Household Products Database
- Health Canada (2010) Cosmetic Ingredient Hotlist
- Health Canada (2006) Food Additives Permitted for Use in Canada
- Government of Canada (2010) Chemicals Management Plan – List of all Challenge Substances
- US Department of Health and Human Services (2005) NTP 11th Report on Carcinogens for Styrene-7,8-oxide
