Water Quality Standards

Summary information extracted from: Guidelines for drinking-water quality, 2nd ed. - Vol. 1. Recommendations. - Geneva, World Health Organization, 1993. pp. 66-67.

Styrene, which is used primarily for the production of plastics and resins, is found in trace amounts in surface water, drinking-water, and food. In industrial areas, exposure levels from air can be a few hundred micrograms per day. Smoking may increase daily exposure by up to 10-fold.

Following oral or inhalation exposure, styrene is rapidly absorbed and widely distributed in the body, with a preference for lipid depots. It is metabolized to the active intermediate styrene-7,8-oxide, which is conjugated with glutathione or further metabolized. Metabolites are rapidly and almost completely excreted in urine.

Styrene has a low acute toxicity. Upon occupational exposure, irritation of mucous membranes, depression of the central nervous system, and possibly hepatoxicity can occur. In short-term toxicity studies in rats, impairment of glutathione transferase activity and reduced glutathione concentrations were observed.

In in vitro tests, styrene has been shown to be mutagenic in the presence of metabolic activation only. In in vitro as well as in in vivo studies, chromosomal aberrations have been observed, mostly at high doses of styrene. The reactive intermediate styrene-7,8-oxide is a direct-acting mutagen.

In long-term studies, orally administered styrene increased the incidence of lung tumours in mice at high dose levels but had no carcinogenic effect in rats. Styrene-7,8-oxide was carcinogenic in rats after oral administration. IARC has classified styrene in Group 2B. The available data suggest that the carcinogenicity of styrene is due to overloading of the detoxification mechanism for styrene-7,8-oxide (e.g., glutathione depletion).

A TDI of 7.7 µg/kg of body weight was derived using a NOAEL of 7.7 mg/kg of body weight per day in a 2-year drinking-water study in rats and applying an uncertainty factor of 1000 (100 for intra- and interspecies variation and 10 for carcinogenicity and genotoxicity of the reactive intermediate styrene-7,8-oxide). This yields a guideline value of 20 µg/litre (rounded figure), allowing 10% of the TDI from drinking-water. It should be noted that styrene may affect the acceptability of drinking-water at this concentration (see Acceptability aspects).