Acetonitrile

CAS RN: 75-05-8

Toxicity Summary

IDENTIFICATION AND USE: Acetonitrile is a liquid with an ether like odor. It is a volatile highly polar solvent used in many different industrial applications including use for the hydrocarbon extraction processes, especially for butadiene; intermediate; catalyst; separation of fatty acids from vegetable oils; and manufacturing of synthetic pharmaceuticals. It is also the starting material for many types of nitrogen-containing compounds, It can be metabolized to produce hydrogen cyanide, which is the source of the observed toxic effects. HUMAN EXPOSURE AND TOXICITY: Symptoms and signs of acute acetonitrile intoxication include chest pain, tightness in the chest, nausea, emesis, tachycardia, hypotension, short and shallow respiration, headache, restlessness and seizures. The systemic effects appear to be attributable to the conversion of acetonitrile to cyanide. Blood cyanide and thiocyanate levels are elevated during acute intoxication. Fatalities after exposure to acetonitrile in the workplace and fatal cases of a child ingesting an acetonitrile containing cosmetic have been reported. Elevated tissue cyanide concentrations were found in postmortem examination of these cases. Acetonitrile is readily absorbed from the gastrointestinal tract, through the skin and the lungs. All three routes of exposure have been reported to lead to systemic effects. No epidemiological study of cancer incidence could be located. ANIMAL STUDIES: There are substantial data to suggest that most of the systemic toxic effects of acetonitrile are mediated through its metabolism to cyanide, which is catalyzed by the cytochrome P450 monooxygenase system. Cyanide is subsequently conjugated with thiosulfate to form thiocyanate which is eliminated in the urine. Peak concentrations of cyanide in the blood of rats following administration of near lethal doses of acetonitrile approximate concentrations observed following the administration of a lethal dose of potassium cyanide. The peak concentration of cyanide after administration of acetonitrile is delayed by up to several hours as compared to other nitriles. The more rapid rate at which cyanide is produced in the mouse appears to account for the much greater sensitivity of this species to the toxic effects of acetonitrile. A portion of the acetonitrile is also eliminated unchanged in expired air and in the urine. Guinea pigs are also another sensitive species to acetonitrile intoxication. The main symptoms in animals appear to be prostration followed by seizures. Dermal application of acetonitrile causes systemic toxicity in animals. Rats were given gavage doses of 125, 190, or 275 mg acetonitrile/kg from gestational days 6 through 19. An increase in post-implantation loss, with a decrease in viable fetuses, was seen at 275 mg/kg. There were no structural abnormalities in the fetuses derived from acetonitrile-exposed rats. Developmental study in pregnant Syrian golden hamsters exposed up to 8,000 ppm acetonitrile for 1 hour on gestational day 8 and then sacrificed on gestational day 14 demonstrated maternal toxixity and fetotoxicity. Abnormal fetuses exhibiting exencephaly and rib fusions were recovered; surviving litters at 8,000 ppm developed severe axial skeletal dysraphic disorders; one 8,000-ppm fetus exhibited extrathoracic ectopia cordis with accompanying defects in the sternum of the heart. Acetonitrile was not mutagenic in Salmonella typhimurium strain TA97, TA98, TA100, TA1535, or TA1537, with or without metabolic activation. In cultured Chinese hamster ovary cells, acetonitrile produced a weakly positive response in the sister chromatid exchange test without, but not with metabolic activation. A small increase in chromosomal aberrations was observed in cultured Chinese hamster ovary cells treated with acetonitrile in the presence, but not in the absence, of metabolic activation. A significant increase in micronucleated normochromatic erythrocytes was observed in peripheral blood samples from male mice treated with acetonitrile for 13 weeks; the frequency of micronucleated erythrocytes in female mice was not affected by exposure to acetonitrile.
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