Cyanides – information sheet

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  • The Government of Canada conducted a science-based evaluation of cyanides, called a screening assessment, to address the potential for harm to Canadians and the environment.
  • Under the Canadian Environmental Protection Act, 1999 (CEPA, 1999), the risk posed by a substance is determined by considering both its hazardous properties (its potential to cause adverse human health or ecological effects) and the amount of exposure there is to people or the environment. A substance may have hazardous properties; however, the risk to human health or to the environment may be low, depending upon the level of exposure.
  • As a result of this screening assessment, free cyanide and precursors of free cyanide are proposed to be harmful to the environment. Although the 2 free/simple cyanide substances are associated with human health effects, the risk posed by these substances was determined to be low, given the levels to which Canadians would be exposed. The 10 cyanide substances assessed for human health are not proposed harmful to human health at current levels of exposure.

About these substances

  • This screening assessment focuses on cyanide substances that are being assessed as part of the third phase of the Chemicals Management Plan (CMP).
  • The ecological screening assessment of cyanides used a moiety-based approach that focuses on free (unbound) cyanide [hydrogen cyanide (HCN) and the cyanide anion (CN-)] and precursors of free cyanide. These are the forms of cyanide of primary ecotoxicological significance. HCN is considered the moiety of ecological concern for cyanides and is expected to be the dominant free cyanide form in the environment. The ecological moiety assessment includes the 10 cyanide substances that were identified as priorities for assessment through the categorization process of the CMP.
  • The human health screening assessment focused on the 10 prioritized cyanide substances. These 10 can be separated into two subgroups: free/simple cyanides [HCN and sodium cyanide (NaCN)] and metal-cyanide complexes. The metal-cyanide complexes are further divided into 3 subgroups: single-iron (3 substances); multi-iron (3 substances); and gold- and silver- cyanide complexes (2 substances).
  • A number of cyanides are naturally occurring substances that may be produced in the environment by both abiotic (for example, through combustion) and biotic (for example, by plants) processes. Forest and house fires and vehicle emissions may release free cyanide to air and water, while many plant-based edible foods contain cyanogenic glucosides (CGs) which may also release free cyanide.
  • In Canada, cyanides are incidentally manufactured by a few industrial sectors where high temperature and pressure processes are used. For example, cyanides are produced incidentally in the coke making and the blast furnace of integrated iron and steel manufacturing plants. Releases of cyanides to air and surface water may occur from these activities.
  • Cyanides are imported into Canada for use by many sectors for a variety of applications, including as analytical reagents for plating and surface finishing and to use as chemical intermediates.
  • Industry data collected by the Government indicates that NaCN is imported into Canada in significant volumes. It is used industrially in large volumes, mainly as an extraction agent for precious metals (for example, gold) and base metals. It may be released in the effluent of metal mining facilities.
  • Some of the metal-cyanide substances are present in products available to consumers, such as natural health products, cosmetics, paints and coatings. Tetrasodium ferrocyanide and tetrapotassium ferrocyanide are approved food additives with limited permitted uses. Tetrasodium ferrocyanide is mainly used as an anti-caking agent in road salts.
  • In 2001, the Government investigated the use of ferrocyanides as anti-caking agents under the Priority Substances List (PSL) Assessment Report for Road Salts. It was determined in that assessment that sensitive species of aquatic microorganisms, plants, invertebrates, and vertebrates in roadside ditches and water courses could experience potential adverse effects from ferrocyanides used in road salts.

Exposure of Canadians and the environment

  • The ecological assessment focused on exposures from the potential release of free cyanide (HCN and CN-) from 3 main sectors of activity: metal mining, iron and steel manufacturing, and application of ferrocyanide-containing road salts. These scenarios were developed since they use or release large quantities of cyanides and they may release cyanides to the aquatic environment.
  • When available, measurements of certain cyanides were considered in addition to measurements of total cyanide (CNT) in the environment. This included measured concentrations in samples from areas receiving metal mining effluent and concentrations in the environment receiving runoff from parking lots and highways where ferrocyanide-containing road salts were applied.
  • Monthly quantities of released total cyanides reported to the Ontario provincial government were also used to calculate average yearly releases of total cyanides to the environment from integrated steel mills.
  • For the human health assessment, potential exposures to free/simple cyanides and certain metal-cyanides from the environment (for example, HCN in air), food, and the use of products were considered.
  • For the cyanides substances used in products available to consumers, exposures were estimated to be minimal or not expected.

Key health and ecological effects (hazard)

  • The aquatic environment is considered the most important medium for cyanides due to the high solubility of free cyanide and many of its precursors. HCN disrupts energy metabolism in organisms and it is highly toxic to aquatic organisms. Free cyanide is also an endocrine-active compound that may disrupt reproduction and other biochemical processes at low concentrations.
  • The ecotoxicity of metal-cyanide is largely driven by its ability to separate and release free cyanide (HCN and CN-).
  • For human health, the important or "critical" effects considered in the assessment of the 2 free/simple cyanide substances (HCN and NaCN) were chronic effects (caused by repeated, low-dose exposure) on the thyroid and effects on the male reproductive system.

Risk assessment outcomes

  • In this screening assessment of cyanides, a risk quotient analysis was done to determine whether there is potential for ecological harm in Canada, specifically for aquatic environments. The analysis combined measured concentrations and estimates of environmental exposure with chronic toxicity information for free cyanide.
  • Measured or estimated exposure concentrations of CNT in surface water downstream of metal mines and iron and steel mills, or as a result of the application of ferrocyanide-containing road salts, were found to exceed the long-term predicted no-effect concentration (PNEC; the concentration below which exposure to a substance is not expected to cause adverse effects in the environment) for free cyanide.
  • Considering all information presented, it was determined that there is risk of harm to organisms but not to the broader integrity of the environment from cyanides, which include free cyanide and precursors of free cyanide.
  • Also, free cyanide and precursors of free cyanide are proposed to meet the persistence criteria, but not the bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations of CEPA 1999.
  • Free/simple cyanides have been assessed by other national and international regulatory agencies, including the United States Environmental Protection Agency and the Food and Agriculture Organization (FAO)/World Health Organization (WHO) [Joint FAO/WHO Expert Committee on Food Additives (JECFA)]. These reports were used to inform the current screening assessment for human health.
  • The risk to human health was characterized for exposures to free/simple cyanides from foods and from air. Based upon a comparison of levels to which Canadians can be exposed to the free/simple cyanides subgroup (2 substances) and levels associated with health effects, it was determined that the risk to human health for these 2 substances is considered to be low.
  • As a result of this assessment, the risk to human health is also considered to be low for the 8 metal-cyanide complexes (single-iron, multi-iron, and gold- or silver- cyanide complexes). Exposures were either not expected or negligible, or adverse health effects were not expected for these 8 substances.
  • The Government published the Draft Screening Assessment for Cyanides on February 10, 2018. This publication has a 60-day public comment period ending on April 11, 2018.

Proposed screening assessment conclusions

  • As a result of this screening assessment, the Government is proposing that the 10 cyanides identified as priorities for assessment are not harmful to human health at current levels of exposure.
  • The Government is also proposing that free cyanide and precursors of free cyanide are entering the environment at concentrations that may be harmful to the environment.

Preventive actions and reducing risk

  • The Government published the proposed Risk Management Scope for Cyanides on February 10, 2018. This publication has a 60-day public comment period ending on April 11, 2018.
  • The Government intends to add free cyanide, cyanide salts and cyanide complexes to Schedule 1 of CEPA 1999, also called the List of Toxic Substances.
  • If the proposed conclusion is confirmed in the final screening assessment, the Government is considering measures to reduce releases of cyanide to water from the following industrial sectors:
    • Metal mining: as part of the proposed amendments to the Metal Mining Effluent Regulations (MMER), Environment and Climate Change Canada (ECCC) will lower the limits for total cyanide in effluent from mining facilities to reduce the risks on fish and fish habitat. ECCC will continue to monitor compliance with the new limits as well as the results of the Environmental Effects Monitoring program to assess the effectiveness of these amendments.
    • Road salts: work with the road salt mining sector, road salt importers, and road salt users to determine the feasibility of controlling the concentration of ferrocyanide salt in road salts or its release to the environment.
    • Integrated iron and steel manufacturing: work with the industry and the Government of Ontario to gather additional information to determine whether there is a need to further limit cyanide concentrations released from mill wastewater treatment effluent.
  • The Government is seeking further information to inform risk management decision-making. Details can be found in the risk management scope, including where to send information during the public comment period, ending April 11, 2018.
  • Further information and updates on risk management actions can be found in the CMP risk management actions table and the risk management activities and consultations schedule.

Important to know

  • Cyanide has high acute toxicity and can cause significant central nervous system effects in humans. Such acute exposures leading to adverse effects in the general population of Canada are rare and are not the focus of this screening assessment.
  • Cyanide substances may be found in products available to consumers. Canadians should follow any safety warnings and directions on product labels and dispose of products responsibly. Some products, such as bitter apricot kernels, naturally contain amygdalin, which can release cyanide after being eaten. Health Canada is reminding Canadians to limit their consumption of bitter apricot kernels because of the risk of cyanide poisoning. They should not be eaten by children.
  • Canadians who may be exposed to cyanide substances in the workplace should consult with their employer and an occupational health and safety (OHS) representative on safe handling practices, applicable laws, and requirements under OHS legislation and the Workplace Hazardous Materials Information System (WHMIS).
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