Cyanides

Overview of Hazards

The cyanide ion CN- is highly toxic because it is an excellent ligand for metals, particularly iron. It can bind to the iron within the protein responsible for the transfer of electrons from cytochrome c to oxygen, preventing aerobic production of ATP in the cell. This causes histotoxic hypoxia in the body. The toxicity of cyanide compounds depends on their solubility and thus, availability of the cyanide ion. All alkali cyanides are highly soluble in water, and exposure to 50 to 200 mg through ingestion or skin contact can cause immediate collapse and death. Symptoms of non-lethal exposures are weakness, headache, dizziness, rapid breathing, nausea, and vomiting.

Inorganic cyanides react with water and atmospheric moisture, liberating highly toxic and flammable hydrogen cyanide (HCN) gas, which poses a serious inhalation hazard. Acids accelerate the reaction causing rapid HCN evolution. Although HCN has a characteristic bitter almond odor, a large percentage of the population cannot detect HCN. 

Safe Handling

Wear standard laboratory attire i.e., closed toe shoes, long pants, a lab coat, eye protection, and nitrile gloves when handling cyanide as powder or in solution. 

Double-glove or wear thicker nitrile rubber gloves if contact with skin is expected. Remove gloves immediately if contaminated and wash hands with soap and water. Always wash your hands after your work is done or when you remove gloves.

Engineering Controls and Work Practices

Handle solid cyanides only in a properly functioning fume hood or other enclosure with an exhaust. Make sure the hood is working properly before you start. 

Put up a warning sign on the work station indicating that cyanides are in use. Never work with cyanides when alone in the lab. Always inform your lab mates before you start your work.

When weighing dry powder and the scale cannot be located inside the enclosure, use the following procedure:

  1. Tare the container with lid.
  2. Add the chemical inside the fume hood and close the container.
  3. Weigh the container.
  4. Add the solvent inside the hood.

If solutions are manipulated in a way that generates aerosols (e.g., sonicating or pressurizing), do this inside the hood if the container has to be open, or keep the container closed. 

Once your work is done, either: Rinse all glassware that came into contact with cyanides with an alkaline bleach solution (pH of 10 or higher) in the hood. This treatment will oxidize cyanide to non-toxic cyanate (CNO-). If the pH is below 10, the reaction can evolve toxic cyanogen chloride (CNCl) and hydrogen cyanide (HCN) gas. Dispose of the rinse as hazardous waste.

Or: Rinse the glassware three times with dilute sodium hydroxide solution (0.1 to 1 mM) in the hood and collect the rinse as cyanide waste. 

After rinsing, clean the glassware with soap and water. The water can go down the sink.

Clean the work area thoroughly by wiping with soap and water once your work is done. 

Emergency Procedures

Rapid medical treatment after exposure is critical to preventing serious injury or death. If cyanide poisoning is suspected, call 911 immediately.

Skin Contact: Remove contaminated clothing and rinse off affected skin immediately with soap and copious amounts of water for at least 15 minutes.

Eye Contact: Use the eye wash to rinse eye thoroughly for at least 15 minutes, occasionally lifting upper and lower eyelids and rolling the eye balls around. 

Inhalation: Move into fresh air immediately.

Ingestion: If the person is conscious, induce vomiting and rinse mouth with water. Seek medical attention immediately.

Provide the medical team with the Safety Data Sheet. An antidote for treating cyanide exposure exists, but it must be administered by properly trained personnel.

Spills

Sweep up spills of solid cyanides carefully, trying to avoid dust formation. Use a cloth dampened with soap water with a pH of 10 if necessary to avoid dust.

Wipe up solutions with chemical absorbent pads. 

Wipe the area thoroughly with water with a pH of 10. Place all clean-up material into heavy-duty plastic bags and seal the bag. Dispose of as hazardous waste. Wipe the area thoroughly with soap and water.

If the spill is outside the hood and too big to handle safely, call 911. Evacuate the area immediately, alerting others. Close the door and prevent people from entering.

Storage

Store cyanides in a cool, dry area away from heat and open flames and separated from incompatible material such as acids, isocyanates, nitrides, and oxidizers.

Disposal

Dispose of all used or unwanted material including dilute solutions through the DRS chemical waste program. Do not treat waste solutions with bleach. Keep cyanide waste separate from all other waste streams, and clearly label the waste container as cyanide waste and “No Acids.” All waste must be disposed of in liquid-tight containers. The container size is limited to one quart (0.94 liters) or less. Larger containers containing cyanide waste will not be picked up. 

References

Agency for Toxic Substances and Disease Registry: Toxicological profile for cyanide, July 2006

International Cyanide Management Code for the gold mining industry

Last Update: 3/24/2014