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The Ministers of Environment and Health have released for final publication the assessment report for the priority substance acrylonitrile. Notice concerning the assessment of this substance and a summary of its assessment report was published in the Canada Gazette, Part 1 May 27, 2000. The synopsis of the report is provided below.

A draft of this Assessment Report was made available for a 60-day public comment period (June 26, 1999 - August 24, 1999). Following consideration of the comments received, the Assessment Report was revised as appropriate. A summary of the comments and their responses may also be accessed from this page.

For paper copies of the Full Assessment Report, please contact the Inquiry Centre at Environment Canada:

To obtain an electronic version of the Assessment Report in PDF, please request a copy from the following address: ESB.DSE@ec.gc.ca

Synopsis

Acrylonitrile is not produced in Canada but is imported and used to produce nitrile-butadiene rubber, acrylonitrile-butadiene-styrene (ABS) polymers and styrene-acrylonitrile (SAN) polymers. In 1994, 7600 tonnes of acrylonitrile were used in Canada, all of which was imported from the United States. It was projected that 8300 tonnes would be used in 1997. There are no known natural sources of acrylonitrile.

The atmosphere and the freshwater aquatic environment receive 97.3% and 2.7% of the releases of acrylonitrile, respectively. The releases are almost exclusively (97.4%) from the organic chemical manufacturing industry - namely, the chemicals and chemical products industry and the plastics industry - and occur in southern Ontario and southern Quebec. Municipal water treatment facilities may release small quantities of acrylonitrile to air via sludge incineration or to water via use of acrylonitrile polymers as conditioners.

Acrylonitrile is distributed largely to the environmental compartment to which it is released, where reaction and advection are the major removal mechanisms. Its movement from the atmosphere or water to soil, sediment or biota is limited.

In general, concentrations of acrylonitrile in air in Canada are below the detection limit. Predicted maximum levels (near a chemical industry processing plant in Sarnia, Ontario) are less than the Estimated No-Effects Value (ENEV) for the most sensitive terrestrial organism. Significant changes over the past 10 years to the treatment of industrial wastewaters have decreased the concentration in effluents discharged to the environment to below 4.2 µg/L. This is less than the ENEV for the most sensitive aquatic organism.

Because of its reactivity in the atmosphere, acrylonitrile's potential contribution to photochemical ozone (and also smog) creation is moderate; however, quantities and concentrations available for reaction (18.75 tonnes in Canada in 1996) make the contribution very low relative to those of other substances. The absence of chlorine and bromine atoms in the acrylonitrile molecule means that its potential contributions to stratospheric ozone depletion and climate change are both negligible.

Although limited, available data are consistent with air being the principal medium of exposure of the general population to acrylonitrile; intake from other media is likely to be negligible in comparison. The focus of the human health risk characterization is populations exposed through air in the vicinity of industrial sources.

Based on studies in animals, cancer is considered the critical endpoint for effects of acrylonitrile on human health. A range of tumours in rats - including those of the central nervous system (brain and/or spinal cord), ear canal, gastrointestinal tract and mammary glands- has been consistently observed following both ingestion and inhalation. While increases in cancer have not been observed in available epidemiological studies, their power is insufficient to rule out increases in particularly rare tumours. Available data are insufficient to support a consensus view on a plausible mode of action for induction of tumours by acrylonitrile by other than direct interaction with genetic material and as a result, there is considered to be a probability of harm at any level of exposure.

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

Based on comparison of worst-case estimates of exposure in air in the vicinity of industrial sources with the tumorigenic potency, it is recommended that options to reduce exposure in the vicinity of industrial point sources be investigated. It is also recommended that there be additional investigation of the magnitude of exposure of populations in the vicinity of industrial point sources as a basis for risk management.