Styrene and Styrene-7,8-Oxide Profile
INDUSTRIAL CHEMICALS – PROBABLE CARCINOGEN (IARC 2A)
Contents
Styrene and Styrene-7,8-Oxide Profile
General Information
Both styrene and styrene-7,8-oxide are sweet-smelling liquids that appear colourless or yellow in colour.[1] Produced since the 1920’s, styrene is one of the most important monomers worldwide.[2] 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.[1] Styrene-7,8-oxide may be referred to as phenyloxirane or styrene oxide.[1,5] There are numerous other synonyms and product names for both styrene and styrene-7,8-oxide; see the Hazardous Substances Data Bank (HSDB) for more information.[5]
Styrene has been classified by the International Agency for Research on Cancer (IARC) as Group 2A, probably carcinogenic to humans, based on limited human and sufficient animal evidence.[4] Elevated incidence or mortality of lymphohematopoietic cancers was observed in large occupational cohorts of workers in the reinforced plastics industry from Europe, the UK, Denmark, and the United States. In particular, there was greater consistency in evidence for myeloid leukaemia; one study found increasing incidence of myeloid leukaemia with increasing cumulative exposure, and another found increased mortality associated with the highest cumulative styrene exposure group. In multiple studies of mice, increased incidence of lung cancers was observed in male and females. Other studies found increased incidence of mammary tumours and liver cancers in females. In addition to the animal and human evidence, there was strong mechanistic evidence that supported the decision.
Styrene-7,8-oxide has been classified by IARC as Group 2A, probably carcinogenic to humans, based on sufficient animal and strong mechanistic evidence.[4] Styrene-7,8-oxide caused forestomach cancer in rats and mice, as well as mammary tumours in rats, and liver tumours in male 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 irritate eyes and throat, and cause dermatitis and a syndrome called “styrene sickness” characterized by feelings of unsteadiness, headache, weakness, and decreased nerve conduction.[5] Exposure to styrene-7,8-oxide causes skin irritation and sensitization.[5]
Regulations and Guidelines
Occupational exposure limits (OEL)[6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
| Styrene | |
|---|---|
| Canadian Jurisdictions | OEL (ppm) |
| Canada Labour Code | 20 40 [stel] |
| AB, BC, MB, NB, PE, SK, NU, NT | 20 40 [stel] |
| NL, NS | 10 [OTO] 20 [stel] |
| ON | 35 100 [stel] |
| QC | 50 [sk] 100 [stel] |
| YT | 100 125 [stel] |
| Other Jurisdictions | OEL (ppm) |
| ACGIH 2020 TLV | 10 [OTO] 20 [stel] |
ppm = parts per million
stel = short term exposure limit (15 min. maximum)
OTO = ototoxicant; potential for a chemical to cause hearing impairment alone or in combination with noise
sk = easily absorbed through the skin
ACGIH = American Conference of Governmental Industrial Hygienists
TLV = threshold limit value (8 hour maximum)
No occupational exposure limits are available for styrene-7,8-oxide in Canada or from the ACGIH.
Canadian environmental guidelines
| Jurisdiction | Limit | Year |
|---|---|---|
| Manitoba Ambient Air Quality Guideline | 24 hour: 400 µg/m3 MALC | 2005[21] |
| Alberta Ambient Air Quality Objectives & Guidelines | 1 hour: 215 µg/m3 | 1999[22] |
| Ontario Ambient Air Quality Criteria | 24 hour: 400 µg/m3 | 2016[23] |
| Government of Canada’s Indoor Air Reference Levels | 850 µg/m3 (critical effect: neurotoxicity; for styrene) | 2018[24] |
| Quebec’s Clean Air Regulation | 1 hour limit: 150 µg/m3 (styrene monomer). The limit may be exceeded up to 2% of the time on an annual basis, without exceeding 1,910 µg/m3 | 2011[25] |
| BC’s Contaminated Sites Regulation, BC Reg 375/96 (styrene) | Sets soil standards for the protection of human health: Agricultural and low density residential sites: 8,500 μg/g Urban park and high density residential sites: 15,000 μg/g Commercial sites: 50,000 μg/g Industrial sites: >1,000 mg/g
Drinking water: 800 µg/L Sets vapour standards for the protection of human health: |
2017[26] |
µg/m3 = micrograms per cubic metre
µg/g = micrograms per gram
MALC = maximum allowable concentration level
Canadian agencies/organizations
| Agency | Designation/Position | Year |
|---|---|---|
| Health Canada | DSL – low priority substance with risks already managed (styrene) | 2006[27] |
| National Classification System for Contaminated Sites | Rank = “High hazard” | 2008[28] |
| PMRA list of formulants | List 4B: List 4B contains formulants, some of which may be toxic, for which there are sufficient data to reasonably conclude that the specific use pattern of the pest control product will not adversely affect public health and the environment. | 2020[29] |
| Environment Canada’s National Pollutant Release Inventory | NPRI Part (Threshold Category): 1A, Reportable to NPRI if manufactured, processed, or otherwise used at quantities greater than: 10 tonnes; 5, Reportable to NPRI if released at quantities greater than: 1 tonne of 10-tonne total VOC air release | 2016[30] |
Styrene-7,8-oxide was removed from the domestic substances list (DSL) in 2013.[31]
Styrene and styrene-7,8-oxide were not included in other Canadian government guidelines, standards, or chemical listings reviewed.
Main Uses
Styrene is used primarily in manufacturing:[4,32]
- Polystyrene resins for plastic packaging, disposable cups, containers, and insulation
- Copolymers 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 to manufacture pipes, automobile parts, food containers, and carpet backing
Styrene is also used to manufacture styrene-butadiene (SB) latex and styrene-butadiene rubbers.[32] 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 producing glass-reinforced plastics.[33]
Styrene-7,8-oxide is used as a chemical intermediate in producing styrene glycol, cosmetics, surface coatings, treatment of fibres and textiles, as well as agricultural and biological chemicals.[5,32] It is also used to produce epoxy resins and the perfume chemical 2-phenylethanol.[5,32]
Canadian Production and Trade
Production and trade
| Activity | Quantity | Year | |
|---|---|---|---|
| Export | 478,950 t of ‘styrene’ | 2021[34] | |
| Export | 95,254 t ‘polymers of styrene’ | 2021[34] | |
| Import | 1,206 t of ‘styrene’ | 2021[34] | |
| Import | 223,199 t of ‘polymers of styrene’ | 2021[34] | |
t = tonne
Canadian production and trade information was not available for styrene-7,8-oxide in the industry databases reviewed.[34]
Environmental Exposures Overview
The general population is most commonly exposed to styrene via indoor air.[1] Styrene can enter the air from industrial releases, vehicle exhaust, incineration emissions, and tobacco smoke.[1,4,34] Between 2009 and 2011, over 3,000 homes were sampled for styrene in Canada; average levels were 1.13 µg/m3, an increase compared to the average levels found in a similar study conducted in 1992 (0.30 µg/m3). Indoor sources contributed to indoor styrene concentrations to a greater extent than outdoor sources.[35]
Environmental exposure to styrene-7,8-oxide may occur by inhaling contaminated air and consuming contaminated water and foods.[36] However, general public exposure is expected to be low as environmental releases of styrene-7,8-oxide from industrial sites are low in both Canada and the US.[36,37]
Low levels of naturally occurring styrene have been found in a number of foods including fruits, vegetables, nuts, beverages, and meats.[38] Small amounts of styrene and styrene-7,8-oxide may also migrate to different foods from styrene-based plastic food packaging.[32,33,38] A typical amount of styrene migration from packaging into food ranges from 5-30 parts per billion (ppb).[38] One UK study estimated that the migration of styrene-7,8-oxide into food is in the range of 0.002-0.15 ppb.[32] In the 2007 Canadian Total Diet Study, styrene was found in 133 of 153 composite samples. Styrene levels in most of these samples were low, but higher levels were found in herbs and spices, in which styrene naturally forms upon degradation.[39]
Searches of Environment Canada’s National Pollutant Release Inventory (NPRI) and the US Consumer Product Information Database yielded the following results on current potential for exposure to styrene in Canada:
NPRI and US Consumer Product Information Database
| NPRI 2015[37] | |
|---|---|
| Search Term: | ‘styrene’ |
| Results | 89 facilities |
| Category | Quantity | Industry |
|---|---|---|
| Released into Environment | 1,450 t | Manufacturing of plastics, glass, transportation equipment, resin, rubber, synthetic fibres, and filaments |
| Disposed of | 278 t | |
| Sent to off-site recycling | 2.4 t |
t = tonne
| US Consumer Products 2016[40] | ||
|---|---|---|
| Search Term | Quantity | Product Type |
| ‘styrene’ | 14 | Automotive paints (2), adhesives (2), wood fillers (3), cements (3), and sealants (4) |
Occupational Exposures
Inhalation is the most important route of occupational exposure to styrene.[1]
CAREX Canada estimates that approximately 71,000 Canadians are likely exposed to styrene in their workplaces. The largest industrial groups exposed to styrene are automotive repair and maintenance, building finishing contractors, and plastic products manufacturing. The largest occupational groups exposed include automotive service technicians, motor vehicle body repairers, plastics processing machine operators, and furniture finishers and refinishers.
For workers involved in manufacturing polystyrene, styrene-butadiene (SB) rubber, acrylonitrile butadiene styrene (ABS) resins, and glass-reinforced plastic, exposure levels can be higher (generally <100 ppm, but higher levels have been reported).[1] Reinforced plastics are used in to make boats, automobile parts, shower stalls, tanks, and tubs.[1] In other styrene exposure scenarios, exposure levels are rarely reported above 20 ppm.[1]
Occupational exposure to styrene-7,8-oxide is primarily due to indirect exposure to styrene. This is because styrene is primarily metabolized via the styrene-7,8-oxide pathway in humans.[4] Styrene-7,8-oxide is also formed when styrene reacts with oxygen in air, or with other oxidizing agents in industrial processes.[3,36] Direct occupational exposure to styrene-7,8-oxide may also occur in workers involved in rubber product and paint manufacturing.[36]
For more information, see the occupational exposure estimate for styrene.
Sources
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