Acetaldehyde

CAS RN: 75-07-0

Exposure Summary

Acetaldehyde's production and use in the manufacture of acetic acid, acetic anhydride, cellulose acetate and many other chemicals may result in its release to the environment through various waste streams. Direct emissions of acetaldehyde occur during urban and industrial activities, mainly as a by-product of combustion. Other direct sources of atmospheric acetaldehyde include biomass and biofuel burning, automobile exhaust and emissions from power plants using fossil fuels, wood or trash. Its use as an ingredient in hydraulic fracturing fluids will result in its direct release to the environment. Acetaldehyde occurs in tobacco smoke. The largest source of atmospheric acetaldehyde is thought to be photochemical degradation of volatile organic compounds such as alkenes and alkanes. In addition to photochemical production, acetaldehyde is emitted directly to the atmosphere by terrestrial plants. Acetaldehyde is found in plants since it is an intermediate product of respiration. Acetaldehyde is produced in surface waters from photodegradation of colored dissolved organic matter and subsequently emitted to the atmosphere. Acetaldehyde is an intermediate product in the decomposition of sugars in the body and occurs in trace quantities in blood. If released to air, a vapor pressure of 758 mm Hg at 20 deg C indicates acetaldehyde will exist solely as a vapor in the atmosphere. Vapor-phase acetaldehyde 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 26 hours. Vapor-phase acetaldehyde will also be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 12 days. Monitoring data have shown that acetaldehyde is removed from the air by wet and dry deposition. Acetaldehyde absorbs at wavelengths >290 nm and is susceptible to direct photolysis by sunlight. The direct photolysis half-life in the atmosphere has reported values of 8.4 hours and 16 hours. The direct photolysis half-life at 55 deg N latitude has been calculated as 34 hours in summer and 296 hours in winter. If released to soil, acetaldehyde is expected to have very high mobility based upon an estimated Koc of 1. Volatilization from moist soil surfaces is expected to be an important fate process based upon a Henry's Law constant of 6.67X10-5 atm-cu m/mole. Acetaldehyde is expected to volatilize from dry soil surfaces based upon its vapor pressure. Utilizing the Japanese MITI test, 80% of the Theoretical BOD was reached in 2 weeks indicating that biodegradation is an important environmental fate process in soil and water. Photodegradation on soil surfaces exposed to sunlight may occur. If released into water, acetaldehyde is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. In a seawater die-away test, acetaldehyde concentrations declined to approximately 25% of initial values in 1 hr, whereas no decline in concentration was observed in sterile controls. 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 11 hours and 5.3 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 lacks functional groups that hydrolyze under environmental conditions. Photodegradation may occur in water exposed to sunlight. Occupational exposure to acetaldehyde may occur through inhalation and dermal contact with this compound at workplaces where acetaldehyde is produced or used. Monitoring data indicate that the general population may be exposed to acetaldehyde via inhalation of ambient air and tobacco smoke, ingestion of food, beverages and drinking water, and dermal contact with consumer products containing acetaldehyde. (SRC)
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