It is generally agreed that the ferrocyanide ion is of a low order of oral toxicity, even in relatively large dosage. Kobert states that potassium ferrocyanide in alkaline solution is nontoxic. In Precis de Toxicologie it likewise is asserted that this salt is nonpoisonous and that it is useful as a diuretic. There is recorded a case of ingestion of a rather sizable dose (30 grams) of potassium ferrocyanide by a man aged 52 which caused serious, but apparently not critical illness. The patient suffered damage to the kidney tubules with marked albuminuria, appearance of casts, and prolonged disturbances of concentration ability. The poisoning was said to be due to the ferrocyanide ion and not to any liberated hydrogen cyanide.

The slow intravenous injection of 5 percent sodium ferrocyanide solution administered to children and adults in clinical tests was without toxic effect. Glomerular function was studied in 45 normal children and adults and in 70 cases with glomerulonephritis, hypertension, and tonsillitis. The results indicate that the quantity excreted by the kidneys is independent of the volume of the urine and is greater than 25 percent in the first thirty minutes.

No case of contact dermatitis attributable to ferrocyanides has been noted in a search of the literature.
Experiments with animals have disclosed significant information about the toxicity of the ferrocyanide ion. With both the sodium and potassium salts, the intraperitoneal LD50 for mice is in the range of 512-1024 mg./kg. Samples of commercial products were administered as 4.1 percent preparations in cotton-seed oil.

Following the injection of sodium ferrocyanide (250-300 mg./kg. of body weight) into dogs, the salt was found in the blood in concentrations of 55-75 milligram-percent. Other investigators have reported that it circulated in the plasma without entering the erythrocytes in measurable amount. It did not appear in the gastric juice or saliva but was eliminated in the urine in concentrations as high as 900-1200 milligram-percent.

Administered to dogs as a solution by stomach tube, sodium ferrocyanide showed the same excretory behavior as inulin and creatinine, with plasma clearance equal to the glomerular filtrate. Clearances and excretion percentages were independent of plasma concentration.

Ferrocyanides Safety 

Although ferrocyanides appear to have a low order of toxicity, highly toxic decomposition products can form under certain conditions. For example, acid, neutral, or basic solutions of ferrocyanides or ferricyanides liberate hydrogen cyanide upon strong or prolonged irradiation (see p. 31). Consequently, in lakes or streams, effluent ferrocyanides that build up to levels exceeding 1-2 p.p.m. may produce cyanide ion or hydrogen cyanide in concentrations lethal to fish.

The mixing of ferrocyanides with hot concentrated acids liberates dangerous concentrations of hydrogen cyanide and carbon monoxide. Therefore, when admixture with acids is desired, adequate ventilation should be provided and the ferrocyanide salts should be added to the previously diluted acids. Tests have shown, however, that the addition of solid sodium ferrocyanide to hot, agitated pickling baths to form concentrations of about 0.15 percent results in the presence of less than 5 p.p.m. of hydrogen cyanide at a point 18 inches above the bath surface. The possibility exists, however, that the level of 20 p.p.m., generally considered dangerous to humans, might be reached if substantially higher concentrations of sodium ferrocyanide were used.

During the many years that the American Cyanamid Company has been manufacturing prussiates, however, none of the plant personnel has ever shown symptoms of ferrocyanide poisoning.