Hydrogen cyanide

CAS RN: 74-90-8

Exposure Summary

Hydrogen cyanide's production and use as a chemical intermediate and for manufacturing nylon and specialty chemicals may result in its release to the environment through various waste streams. Its former use as an insecticidal fumigant, rodenticide and illegal use as a chemical warfare agent resulted in its direct release to the environment. Hydrogen cyanide is present in human blood and some plants. Small concentrations are also found in the stratosphere and atmosphere. If released to air, a vapor pressure of 742 mm Hg at 25 deg C indicates hydrogen cyanide will exist solely as a vapor in the atmosphere. Vapor-phase hydrogen cyanide will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 530 days. Hydrogen cyanide does not contain chromophores that absorb at wavelengths >290 nm and, therefore, is not expected to be susceptible to direct photolysis by sunlight. If released to soil, hydrogen cyanide is expected to have very high mobility based upon an estimated Koc of 15. The pKa of hydrogen cyanide is 9.2, indicating that this compound will exist partially in the anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts. Volatilization from moist soil surfaces is expected to be an important fate process based upon a Henry's Law constant of 1.33X10-4 atm-cu m/mole. Hydrogen cyanide may volatilize from dry soil surfaces based upon its vapor pressure. Hydrogen cyanide can be biodegraded by acclimated microbial cultures and sludges, but is usually toxic at high concentrations to unacclimated microbial systems, indicating that biodegradation may not be an important environmental fate process in soil and water. If released into water, hydrogen cyanide is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. Volatilization from water surfaces is expected to be an important fate process based upon this compound's Henry's Law constant. Estimated volatilization half-lives for a model river and model lake are 5 hrs and 3 days, respectively. An estimated BCF of 3 suggests the potential for bioconcentration in aquatic organisms is low. Hydrolysis is not expected to be an important environmental fate process since this compound contains lacks functional groups that hydrolyze under environmental conditions (pH 5 to 9). Occupational exposure to hydrogen cyanide may occur through inhalation and dermal contact with this compound at workplaces where hydrogen cyanide is produced or used. Monitoring data indicate that the general population may be exposed to hydrogen cyanide via inhalation of cigarette smoke, ingestion of specific foods. (SRC)
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