About CYANIDE

Human toxicity

Cyanides act quickly, they are taken up through the skin and mucous membranes (e.g. in the mouth, stomach and intestines).  They are quickly distributed throughout the body.  They destroy the normal metabolism in the cells so that oxygen cannot be used, and thus cause a cellular choking as well as blocking the respiratory centres in the brain.  They also bind strongly to red blood cells and block the oxygen uptake.  The concentration in human tissues decreases rapidly after a single dose.

The cyanide ion is readily absorbed by the gastrointestinal tract and is rapidly converted into thiocyanate by the enzyme rhodanese.  Cyanide may lower vitamin B12 levels and hence exacerbate vitamin B12 deficiency.  Those with nutritional inadequacy or inborn metabolic errors are particularly vulnerable.

Environmental toxicity

Cyanide toxicity in animals is essentially an inhibition of oxygen metabolism, rendering tissues incapable of exchanging oxygen.  The toxicity of cyanides to marine and freshwater organisms is due mainly to the presence of hydrocyanic acid, HCN and to a lesser degree to the cyanide ion, CN.

The acute toxicity of free cyanide (expressed as CN) to aquatic organisms is highly variable, but may be as low as 0.005 mg/L.

Environmental behaviour

Cyanides are highly susceptible to environmental degradation and residues are often extremely low in surface waters.  Cyanides also accumulate in bottom sediments, but residues are generally low, <1 mg/kg, even near polluting sources.  Many cyanides are presumed to be rapidly sorbed by sediments, clays and biological substances.  They are also degraded by processes such as solar irradiation.  The majority of an accidental release is volatilised to the atmosphere where it is quickly diluted and degraded.  Cyanides are subject to significant biological transformation during anaerobic and aerobic sewage treatment.  The processes are slower in surface waters, but are mediated by bacteria and rate-limited by nutrient levels and dissolved gases.

Bioaccumulation

Many cyanide compounds, including HNC, are rapidly metabolised in biological systems, thereby limiting the potential for bioaccumulation. There is no evidence of bioaccumulation in the food chain, and hence, secondary poisoning is not likely