Styrene (vinylbenzene)
(endorsed 1996)
Guideline
Based on aesthetic considerations (odour), the concentration of styrene in drinking water should not exceed 0.004 mg/L.
Styrene would not be a health concern unless the concentration exceeded 0.03 mg/L.
General description
Styrene may be present in drinking water as a result of contamination from industrial sources. It has occasionally been detected in water supplies in the United States and the Netherlands at concentrations of less than 0.001 mg/L.
The taste threshold of styrene in water at 40°C ranges from 0.02 mg/L to 2.6 mg/L, depending on individual sensitivities. At 60°C the odour threshold in water is 0.004 mg/L.
Styrene is used in the production of plastics and resins. It has been detected in food packaged in polystyrene containers. However, improvements in the use of polystyrene since 1980 have resulted in substantial decreases in the release of the monomer. The daily exposure to styrene has been estimated to be 0.04 mg per person, with smokers receiving a higher dose. Forest fires may contribute to atmospheric concentrations of styrene.
Typical values in Australian drinking water
Styrene has not been found in Australian drinking waters. It is included here to provide guidance in the unlikely event of contamination, and because it has been detected occasionally in drinking water supplies overseas.
Treatment of drinking water
Styrene can be removed from drinking water by reaction with ozone to form aldehydes, ketones and benzoic acid. It can also be adsorbed onto granular activated carbon.
Measurement
A purge and trap gas chromatographic procedure can be used for analysis (USEPA Draft Method 503.1 1986). An inert gas is bubbled through the sample and styrene trapped on an adsorbent. The adsorbent is then heated and styrene analysed using gas chromatography with photoionisation detection. The limit of determination is less than 0.0001 mg/L.
Health considerations
Approximately 60–90% of styrene is absorbed following ingestion or inhalation. It is widely distributed in the body, with a preference for fatty tissues. It is metabolised by a number of tissues and organs to styrene-7,8-oxide.
An extensive review and summary of the human and animal toxicity data for styrene is available (IPCS 1983).
A number of studies have reported on occupational inhalation of styrene. High doses for long periods have resulted in irritation of the respiratory system and some neurotoxic effects on both central and peripheral nervous systems. Chromosomal aberrations in lymphocytes have been associated with high styrene exposures, but not with low concentrations, among workers in the glass fibre industry.
In a long-term study using rats, female body weights were depressed at high doses (250 mg/kg body weight per day). No other treatment-related effects were observed.
Most studies using rodents have not found any association between styrene intake and an increased incidence of tumours. Styrene is mutagenic in a variety of test microorganisms, but only after metabolic activation. It also induces gene mutations and chromosomal aberrations in mammalian cells. The mutagenic agent is probably styrene-7,8-oxide, the main metabolic by-product of styrene and a direct-acting mutagen. Two long-term gavage studies using rats have also reported that styrene-7,8-oxide significantly increased the incidence of fore-stomach tumours at a dose of 250 mg/kg body weight per day.
The International Agency for Research on Cancer has concluded that styrene-7,8-oxide is probably carcinogenic to humans (Group 2A, inadequate evidence in humans, sufficient evidence in experimental animals, and supporting mechanistic evidence) (IARC 1994).
Derivation of guideline
The assessment of the toxicological data for styrene by the World Health Organization (WHO) has been used without review. The health-based guideline value of 0.03 mg/L was determined as follows:
where:
7.7 mg/kg body weight per day is the no-effect level based on a 2-year drinking water study using rats (Beliles et al. 1985).
70 kg is the average weight of an adult.
0.1 is the proportion of total daily intake attributable to the consumption of water.
2 L/day is the average amount of water consumed by an adult.
1000 is the safety factor in using the results of an animal study as a basis for human exposure (10 for interspecies variations, 10 for intraspecies variations and 10 for carcinogenic and genotoxic effects).
This health-based value is greater than the odour threshold of 0.004 mg/L.
The WHO guideline value of 0.02 mg/L was based on an adult body weight of 60 kg. The difference in guideline values is not significant.
References
Beliles RP, Butala JH, Stack CR, Makris S (1985). Chronic toxicity and three-generation reproduction study of styrene monomer in the drinking water of rats. Fundamental and Applied Toxicology, 5:855–868.
IARC (International Agency for Research on Cancer) (1994). IARC Monographs on the Evaluation of World Health. Carcinogenic Risks to Humans: Some Industrial Chemicals. World Health Organisation, IARC, 60, Lyons.
IPCS (International Programme on Chemical Safety) (1983). Styrene. Environmental Health Criteria, 26. World Health Organization, IPCS.
USEPA Draft Method 503.1 (1986). Volatile organic compounds in water by purge and trap gas chromatography. United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory (EMSL), Cincinnati, Ohio.
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