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The Ministers of Environment and Health have released for final publication the assessment report for the priority substance carbon disulfide. 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 (October 23, 1999 - December 22, 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

Carbon disulfide is commercially produced in Canada, with annual production of about 3 kilotonnes. It is mainly used as a precursor in the manufacture of xanthates, which are used as flotation agents in mineral refinery processes. Releases into the environment from human activities occur primarily as a result of its production as a by-product in oil and gas processing in Canada. Additional industrial releases result from its use in the chemical industry and tire manufacturing. Virtually all anthropogenic and natural releases are to air. Carbon disulfide is also produced naturally by several types of soil, sediment and aquatic microorganisms, vegetation, forest and grass fires and volcanoes. Worldwide, at least 40% and possibly as much as 80% of releases are a result of natural or biogenic activity.

Carbon disulfide is ubiquitous throughout the environment. It has been detected in air, water, sediment and soil; however, it is found primarily in air. The highest concentrations of carbon disulfide in Canadian air have been measured near industrial sources, in particular near natural gas processing plants and sites with sulfur-containing natural gas flares. Carbon disulfide is removed from the air primarily by reaction with hydroxyl radicals, resulting in a half-life of 1-2 weeks. This half-life in air makes it a candidate for long-range transport; however, it is rapidly diluted to natural background levels. Carbon disulfide is rapidly metabolized by organisms and does not bioconcentrate or biomagnify.

As carbon disulfide is mainly released to and detected in air, this is a critical compartment in the assessment of risk to the environment. In situations where carbon disulfide-containing effluents are released to surface waters, biota in water may be exposed. Selected assessment endpoints are, therefore, terrestrial plants and animals and freshwater organisms. Carbon disulfide is of moderate to low toxicity to aquatic biota.

Based on concentrations measured in air and surface water in Canada and on the Estimated No-Effects Values derived from experimental data for terrestrial and aquatic biota, it is unlikely that organisms are exposed to harmful levels of carbon disulfide in the Canadian ambient environment.

Carbon disulfide is not likely to contribute significantly to depletion of stratospheric ozone, ground-level ozone formation or climate change.

Available data upon which to base estimates of human exposure to carbon disulfide in Canada are extremely limited; however, air appears to be the major route of exposure for members of the general population. Airborne exposures are estimated to be elevated for populations in the vicinity of industrial point sources in Canada. Based on the results of epidemiological studies of workers exposed to carbon disulfide and supporting data from experiments conducted on animals, the nervous system appears to be the critical target for carbon disulfide-induced toxicity, manifested most often as reduced conduction velocity in the peripheral nerves and impaired performance in psychomotor testing. Other effects for which there is considerable weight of evidence in humans exposed to carbon disulfide include alterations in serum lipids and blood pressure that are associated with increased risk of heart disease, damage to the blood vessels of the retina and (with higher exposures) increased mortality from heart disease. The estimated mean airborne exposure to carbon disulfide for the general population, and for populations in the vicinity of point sources, is considerably less than a Tolerable Concentration derived on the basis of a benchmark concentration for reduced peroneal motor nerve conduction velocity in a population of viscose rayon workers exposed to carbon disulfide. A Tolerable Concentration is the level to which it is believed a person may be exposed daily over a lifetime without deleterious effect.

Based on the information available, it is concluded that carbon disulfide 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, that constitute or may constitute a danger to the environment on which life depends, or that constitute or may constitute a danger in Canada to human life or health. Therefore, carbon disulfide is not considered to be "toxic" as defined in Section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999).

The evaluation of options under CEPA 1999 to reduce exposure is not considered to be a priority at this time. However, this is based on current use patterns; thus, future releases of this compound should continue to be monitored to ensure that exposure does not increase to any significant extent.