Page 3: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Benzene

Part I. Overview and Application - Continued

2.0 Executive summary

Although benzene is naturally occurring at low concentrations, its presence in the environment is mostly related to human activities. Gasoline contains low concentrations of benzene (below 1%), and emissions from vehicles are the main source of benzene in the environment. Benzene can be introduced into water by industrial effluents and atmospheric pollution.

This Guideline Technical Document reviews and assesses all identified health risks associated with benzene in drinking water, incorporating multiple routes of exposure to benzene from drinking water, including ingestion and both inhalation and skin absorption from showering and bathing. It assesses new studies and approaches and takes into consideration the availability of appropriate treatment technology. From this review, the guideline for benzene in drinking water is established at a maximum acceptable concentration (MAC) of 0.005 mg/L (5 µg/L). The guideline for benzene is established based on cancer end-points and is considered protective for all health effects.

2.1 Health effects

Benzene is classified as a human carcinogen. Both animal and human studies report similar toxic effects from exposure to benzene. The most sensitive effects are found in the bloodforming organs, including the bone marrow.

The MAC for benzene in drinking water is established based on the incidence of bone marrow effects and malignant lymphoma in mice, through the calculation of a lifetime unit risk.

2.2 Exposure

For most Canadians, the major source of exposure to benzene is air; this accounts for an estimated 98-99% of total benzene intake for Canadian non-smokers. Like food, drinking water is considered to be only a minor source of exposure to benzene.

Benzene can be found in both surface water and groundwater sources, but it is not generally a concern in surface water, because benzene tends to evaporate into the atmosphere. Some provinces and territories across Canada have detected benzene in drinking water supplies; however, data collected indicate that the levels are generally below the MAC of 0.005 mg/L.

2.3 Analysis and treatment

The establishment of a drinking water guideline must take into consideration the ability to both measure the contaminant and remove it from drinking water supplies. Benzene can be reliably measured to concentrations as low as 0.4 µg/L, which is below the MAC.

Several municipal-scale treatment processes can remove benzene from drinking water to levels below 0.005 mg/L. At the residential scale, drinking water treatment devices are available that have been certified to reduce the concentrations of volatile organic compounds (VOCs), including benzene, to below 0.005 mg/L, although lower levels may be achieved with the use of these devices.

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