Acetonitrile

CAS RN: 75-05-8

Exposure Summary

Acetonitrile's production and use in solvent extraction, reaction media, and as an intermediate in the preparation of pharmaceuticals and other organic chemicals may result in its release to the environment through various waste streams. Acetonitrile occurs in coal tar in small amounts, has been detected in volcanic gases and quantified in emissions from the combustion of wood and other biomass. If released to air, a vapor pressure of 88.8 mm Hg at 25 deg C indicates acetonitrile will exist solely as a vapor in the ambient atmosphere. Vapor-phase acetonitrile 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 610 days. Vapor-phase acetonitrile will also be degraded in the atmosphere by reaction with ozone; the half-life for this reaction in air is estimated to be greater than or equal to 76 days. Acetonitrile does not absorb at wavelengths >290 nm and direct photolysis by sunlight is not expected to be an important fate process. The removal of acetonitrile from the atmosphere by precipitation has been reported to be an important fate process. If released to soil, acetonitrile is expected to have very high mobility based upon a Koc of 2.2. Volatilization from moist soil surfaces is expected to be an important fate process based upon a Henry's Law constant of 3.45X10-5 atm-cu m/mole. Acetonitrile is expected to volatilize from dry soil surfaces based upon its vapor pressure of 88.8 mm Hg. Utilizing the Japanese MITI test, 65% of the Theoretical BOD was reached in 4 weeks indicating that biodegradation may be an important environmental fate process in soil and water. Available screening studies suggest that acetonitrile is readily biodegradable by adapted microbial populations, but biodegradation is generally slower with non-adapted microbes. If released into water, acetonitrile is not expected to adsorb to suspended solids and sediment based upon its Koc value. 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 12 hours and 7.5 days, respectively. An estimated BCF of 3 suggests bioconcentration in aquatic organisms is low. The biodegradability of acetonitrile in river water had an observed 12-day ThOD (theoretical oxygen demand) of 40%. In acclimated river water, 100% removal was observed after 4 days. Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions. Occupational exposure to acetonitrile may occur through inhalation and dermal contact with this compound at workplaces where acetonitrile is produced or used. Monitoring data indicate that the general population may be exposed to acetonitrile via inhalation of ambient air and ingestion of food. (SRC)
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