Print | Need Larger Text? | Share

Priority Substances List Assessment Report- 1,3-Butadiene

Synopsis

1,3-Butadiene (hereafter referred to as butadiene) is a product of incomplete combustion resulting from natural processes and human activity. It is also an industrial chemical used primarily in the production of polymers, including polybutadiene, styrene-butadiene rubbers and latexes, and nitrile-butadiene rubbers. Butadiene enters the Canadian environment from exhaust emissions from gasoline- and diesel-powered vehicles, from non-transportation fuel combustion, from biomass combustion and from industrial on-site uses. The total amount of butadiene entering the Canadian environment was estimated to range from 12 917 to 41 622 tonnes in 1994, mostly into air.

While butadiene is not persistent, it is ubiquitous in the urban environment because of its widespread combustion sources. Highest atmospheric concentrations have been measured in air in cities and close to an industrial source. Given its sources of entry into the environment, its environmental fate and concentrations measured in Canada, the environmental assessment focussed on assessing the potential risks to aquatic life, terrestrial plants, terrestrial wildlife and soil invertebrates. The potential risks were assessed assuming worst-case, hyperconservative conditions. Analyses indicate that environmental biota are unlikely to be at risk even under such conditions.

Because of its non-halogenated nature and moderate environmental concentrations, butadiene is not associated with stratospheric ozone depletion or with climate change. Butadiene is a reactive chemical with a high photochemical ozone creation potential and moderate concentrations in air, and therefore is a contributor to the formation of ground-level ozone and resulting smog formation.

The general population in Canada is exposed to butadiene primarily through ambient and indoor air. Inhaled butadiene is carcinogenic in both mice and rats, inducing tumours at multiple sites at all concentrations tested in all identified studies. In addition, butadiene is genotoxic in both somatic and germ cells of rodents. The greater sensitivity in mice than in rats to induction of these effects by butadiene is likely related to species differences in metabolism to active epoxide metabolites. An association between exposure to butadiene in the occupational environment and leukemia fulfils several of the traditional criteria for causality; there is also some limited evidence that butadiene is genotoxic in exposed workers. Therefore, in view of the weight of evidence of available epidemiological and toxicological data, butadiene is considered highly likely to be carcinogenic in humans; it is also considered likely to be genotoxic in humans. Butadiene also induced adverse effects in the reproductive organs of female mice at relatively low concentrations.

Based on the information available, it is concluded that butadiene is not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity. However, butadiene is concluded to be entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger to the environment on which life depends and a danger in Canada to life or health. Therefore, butadiene is considered to be "toxic" as defined in Section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999).

Butadiene contributes to the photochemical formation of ground-level ozone. It is recommended that key sources of butadiene be addressed, therefore, as part of management plans for volatile organic chemicals that contribute to the formation of ground-level ozone.

Based on comparison of estimates of exposure for the general population with the tumorigenic potency, the priority to investigate options to reduce exposure to butadiene in ambient air in the vicinity of the identified point sources is considered to be high, while that from more dispersive non-point sources (identified herein primarily as transportation) is considered to be moderate to high. Investigation of concentrations and potential sources of butadiene in indoor air may also be warranted.