The risks posed by a substance are determined by both its hazardous properties (potential to cause adverse human health or ecological effects) and the amount or extent of exposure to people and the environment.
When needed, the Government implements risk management measures under CEPA 1999 and other federal acts to help prevent or reduce potential harm.
As a result of the screening assessment, free cyanide and precursors of free cyanide were concluded to be harmful to the environment, due to potential risk to aquatic organisms from their releases from 3 sectors of activity.
The Government proposed risk management measures to address the ecological concerns.
The Government also concluded that the 10 cyanide substances that were identified as priorities for assessment are not considered harmful to human health at levels of exposure considered in the screening assessment. 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 ecological portion of the screening assessment used a moiety-based approach, which means that all forms of cyanide were considered in the screening assessment. This approach focused on free cyanide [hydrogen cyanide (HCN) and the cyanide anion (CN-)] and precursors of free cyanide. Precursors to free cyanide are substances, such as cyanide salts and cyanide complexes, that contain the cyanide moiety and that can degrade to free cyanide through any transformation at environmentally, industrially, or physiologically relevant conditions.
The human health portion of the screening assessment focused on the 10 prioritized cyanide substances. These substances were separated into 2 subgroups: free/simple cyanides [HCN and sodium cyanide (NaCN)] and metal-cyanide complexes. The metal-cyanide complexes were 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 foods contain cyanogenic glycosides, which may also release free cyanide.
In Canada, cyanides are incidentally produced (made unintentionally) by a few industrial sectors where high temperature and pressure processes are used. For example, cyanides are produced incidentally in the coke ovens and blast furnaces of integrated iron and steel manufacturing plants, and from the manufacture of some chemical substances. Releases of cyanides to air and surface water may occur from these activities.
According to information gathered by the Government, 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 (used to make other substances).
Industry data collected by the Government indicates that NaCN had the highest import quantity. It is used mainly as an extraction agent for precious metals (for example, gold) and base metals, and may be released in the effluent of certain metal mining facilities.
Tetrasodium ferrocyanide is mainly used as an anticaking agent (prevents clumping) in road salts.
In 2001, the Government investigated the use of ferrocyanides as anticaking 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 watercourses in areas of high road salt use could experience potential adverse effects from ferrocyanides.
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 a limited number of permitted uses.
Human and ecological exposures
The screening assessment indicated that Canadians may be exposed to free/simple cyanides and certain metal-cyanides from the environment (for example, HCN in air), food, and the use of certain products available to consumers.
Human exposures to cyanides in products available to consumers were estimated to be minimal.
The ecological assessment focused on exposures from the potential release of cyanides from 3 main sectors of activity: metal mining, iron and steel manufacturing, and application of ferrocyanide-containing road salts. These exposure scenarios focused on release of cyanides to the aquatic environment due to the high water solubility of free cyanide and many of its precursors.
When available, ecological exposure scenarios considered measured or estimated concentrations of free cyanides or weak acid dissociable cyanides in addition to measurements of total cyanide (CNT) in the environment.
In humans, critical health effects from chronic (long-term) exposure to free/simple cyanide substances (HCN and NaCN) are effects on the thyroid and the male reproductive system.
The ecological effects assessment focused on the aquatic environment. Critical ecological effects from chronic exposure to HCN include disruption of energy metabolism and high toxicity to aquatic organisms. HCN may also disrupt reproduction and other biochemical processes at low concentrations.
The ecotoxicity of metal-cyanide complexes is largely driven by their ability to transform and release free cyanide (HCN and CN-).
Consideration of subpopulations who may be more susceptible or highly exposed
There are groups of individuals within the Canadian population who, due to greater susceptibility or greater exposure, may be more vulnerable to experiencing adverse health effects from exposure to substances.
Certain subpopulations are routinely considered throughout the screening assessment process, such as infants, children, and people of reproductive age. For instance, age-specific exposures are routinely estimated and developmental and reproductive toxicity studies are evaluated for potential health effects. These subpopulations were taken into account in the risk assessment outcomes of the cyanides screening assessment.
In addition, people living near high traffic roads are more likely to be exposed to higher levels of HCN in air and were considered in the screening assessment.
Risk assessment outcomes
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.
For the ecological assessment, risk quotient analyses were performed for three exposure scenarios to compare measured or estimated concentrations of cyanides in aquatic environments to concentrations that may cause adverse effects.
Based upon these comparisons, it was determined that releases of free cyanide and precursors to free cyanide may pose a risk to aquatic organisms.
Screening assessment conclusions
The Government concluded that the 10 cyanides identified as priorities for assessment are not harmful to human health at levels of exposure considered in the screening assessment.
The Government also concluded that free cyanide and precursors of free cyanide are entering the environment at concentrations that may be harmful to the environment.
The proposed order adding free cyanide, cyanide salts and cyanide complexes to Schedule 1 to CEPA 1999, also called the List of Toxic Substances, was published for a 60-day public comment period ending on May 17, 2023. Adding a substance to the list does not restrict its use, manufacture or import. Rather, it enables the Government to take risk management actions under CEPA 1999.
To address ecological concerns, the Government is proposing the following actions to reduce human-made releases of cyanides to water from the following industrial sectors:
Metal Mining: monitoring the effects of the lower maximum authorized concentrations of cyanide (came into force on June 1, 2021) in the Metal and Diamond Mining Effluent Regulations (MDMER) on reducing the risks to fish and fish habitat.
Road Salts: working with the road salt mining sector and road salt importers and 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: working with industry and the Government of Ontario to gather additional information to determine whether there is a need to further limit total cyanide concentrations released from mill wastewater treatment effluent.
Information is being sought by the Government to inform risk management decision-making. Details can be found in the proposed risk management approach, including where to send information during the 60-day public comment period.
The risk management actions outlined in this risk management approach may evolve through consideration of assessments and risk management actions published for other substances to ensure effective, coordinated, and consistent risk management decision-making.