Cyanides, total CN

The substance
Cyanides are based on a carbon-nitrogen chemical unit that combines with a variety of organic and inorganic compounds. Cyanides are mainly present as hydrogen cyanide and alkali cyanides such as sodium and potassium cyanide. Hydrogen cyanide is a colourless gas with a characteristic odour (often described as almond like) and miscible with water and slightly soluble in ether (see also substance description 'hydrogen cyanide'). Sodium cyanide and potassium cyanide are both white solids which are soluble in water and also in alcohol. Alkali cyanides may smell of hydrogen cyanide as well as of ammonia, especially when in contact with water.

Use
Alkali cyanides are used in the extraction of gold and silver, as depressants in the extraction of base metals, in chemical synthesis and for surface treatment of metals.

Major emissions
Cyanide is found naturally in the environment in very small quantities, where it can be produced by certain bacteria, fungi, and algae, and it is also found in a number of foods and plants. Cyanides are released to waters from various industrial processes. Metal finishing and organic chemical industry as well as iron and steel production are major sources of cyanide release.

Impacts on human health and environment
Alkali cyanides (and hydrogen cyanide) are very toxic by ingestion, skin contact and by inhalation. All cyanides inhibit oxygen binding respiratory enzymes and consequently the brain and the cardiovascular system are the main organs affected by cyanide poisoning due to their high oxygen demand. Cyanides are generally not persistent when released to water and soil, and are not likely to accumulate in aquatic life. They can rapidly evaporate from water and soils and can be broken down by microbes. They are however very toxic to fish and other forms of aquatic life. All cyanides act as respiratory poisons to aerobic organisms, interfering with oxygen binding to respiratory enzymes. Cyanides generally do not bind to soils and may leach to groundwater. At high concentrations, cyanides are toxic to various soil micro-organisms.

Emission to water reporting threshold: 50 kg/year

Data source: European Pollutant Emission Register