Friday, October 15, 2004

Toxicity

It is not easy to determine what are the lethal doses of cyanide to man. Human cyanide poisoning is associated with a mortality rate of 95 %. Taken orally the fatal dose of HCN to adult is estimated at 50-100 mg, and for potassium cyanide (KCN) , about 150-250 mg. However, victims ingesting as much as 3 g of KCN have been saved with immediate therapy. Inhalation of HCN at a concentration of 270 ppm (approximately 0.3 mg HCN per liter) will be immediately fatal. Victims having a blood cyanide level of 2.5-3.0 µg/ml frequently succumb to respiratory cessation within 20-30 min of exposure or may survive even up to 3 hr4.

Although they are generally considered to be very toxic substances, when compared with other lethal chemical warfare agents, cyanides are among the least toxic. Even in closed room with the introduction of pure gaseous cyanide in high concentrations, as occurred in the Nazi death chambers, death did not occur and was not immediate for a number of minutes3,5. The LCt50 for hydrogen cyanide (hydrocyanic acid) is generally stated to be 2,500-5,000 mg•min/m3; for cyanogen chloride, about 11,000 mg•min/m3. (comparable values for the nerve agents are 10-200 mg•min/m3; for sulfur mustard, 1,500 mg•min/m3; and for phosgene, 3,000 mg•min/m3)3.

The toxicodynamic effect can vary depending on the dose, route and time of exposure, speed of administration, chemical form of the cyanide, and other factors including the gender, age, weight, stress level, and general physical condition of the recipient3,10.
The estimated intravenous dose that is lethal to 50% of the exposed population (LD50) of hydrogen cyanide for man is 1.0 mg/kg, and the estimated LD50 for liquid on the skin is about 100 mg/kg3.

Cyanide induces fatality in seconds to minutes following inhalation or intravenous injection, in minutes following ingestion of soluble salts, or in minutes following ingestion of soluble salts, or minutes (hydrogen cyanide) to several hours (cyanogens) after skin absorption1.
Suicide by cyanide poisoning occurs predominantly in males, as does industrial exposure. And deliberate ingestion of cyanide occurs mostly in adults. Poisoning is enhanced by an empty stomach and high gastric acidity. A full stomach may delay symptoms for up to 4 hours. Smoke inhalation affect all ages. Chronic cyanide poisoning affects children and adults1. The measurement of blood levels has little clinical significance but may be of forensic importance3. Generally, serum levels greater than 1 mg/liter are fatal. Smokers may have incidental serum cyanide levels of 0.1 mg/liter1,3.

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