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Benzene - PSL1

Overview of Findings

Benzene is used in Canada in a variety of ways that result in it entering the Canadian environment. Vehicle emissions are the major source of benzene release to the environment. Releases of benzene result in measurable concentrations in the various media to which humans and other organisms may be exposed.

Except in cases of spills or occasional discharge of contaminated effluent, the highest reported mean concentration of benzene in ambient surface water in Canada is about 2000 times less than that found to induce adverse effects in the most sensitive aquatic species (leopard frog) in long-term studies. The highest mean concentration of benzene in untreated effluents released into surface water is about 80 times less than the levels found to induce adverse effects in the most sensitive aquatic species (rainbow trout) in acute studies. The highest concentration of benzene in ambient air measured in Canada is almost 240 000 times lower than the lowest concentration reported to be lethal to plants, terrestrial invertebrates, and laboratory mammals following acute exposure to benzene in air. The average concentration of benzene in rural air is more than 26 000 times lower than that found to induce adverse effects in laboratory mammals under chronic exposure conditions.

Because of its short persistence in the atmosphere, its nonhalogenated nature, and its low absorption of infrared radiation of critical wavelengths, benzene is not associated with depletion of stratospheric ozone or with global warming.

In Canada, the primary source of human exposure to benzene is ambient and indoor air; food and drinking water contribute only minor amounts to the daily intake of benzene. Benzene has been demonstrated to cause cancer in experimental animals and in humans. Benzene is, therefore, considered to be a "non-threshold toxicant", i.e., a substance for which there is believed to be some chance of adverse effects at any level of exposure. For such substances, estimated exposure is compared to quantitative estimates of cancer potency in order to characterize risk and provide guidance for further action, such as analysis of options to reduce exposure.

Based on these considerations, the Minister of the Environment and the Minister of National Health and Welfare have concluded that benzene is a substance entering the environment in a quantity or concentration or under conditions that do not constitute a danger to the environment or to the environment upon which human life depends, but that may constitute a danger to human life or health in Canada. Therefore, benzene is considered to be "toxic" as defined under Section 11 of the Canadian Environmental Protection Act.