Acetaldehyde

CAS RN: 75-07-0

Environmental Fate

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 1(SRC), determined from a structure estimation method(2), indicates that acetaldehyde is expected to have very high mobility in soil(SRC). Volatilization of acetaldehyde from moist soil surfaces is expected to be an important fate process(SRC) given a Henry's Law constant of 6.67X10-5 atm-cu m/mole(3). Acetaldehyde is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 758 mm Hg at 20 deg C(4). An 80% of theoretical BOD using activated sludge in the Japanese MITI test(5) suggests that biodegradation is an important environmental fate process in soil(SRC). Acetaldhyde was oxidized in a silty clay loam soil but no rates were given(6). Acetaldehyde absorbs at wavelengths >290 nm(7) and is susceptible to direct photolysis by sunlight(8); therefore, photolysis may be an important fate process of soil surfaces exposed to sunlight(SRC).
AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 1(SRC), determined from a structure estimation method(2), indicates that acetaldehyde is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(3) based upon a Henry's Law constant of 6.67X10-5 atm-cu m/mole(4). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 11 hours and 5.3 days respectively(SRC). According to a classification scheme(5), an estimated BCF of 3(SRC), from its log Kow of -0.34(6) and a regression-derived equation(2), suggests the potential for bioconcentration in aquatic organisms is low(SRC). Utilizing the Japanese MITI test(7), 80% of the Theoretical BOD was reached in 2 weeks indicating that biodegradation is an important environmental fate process. In a die-away test in seawater, acetaldehyde concentrations declined to approximately 25% of initial values in 1 hr, whereas no decline in concentration was observed in sterile controls(8). Acetaldehyde is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(3). Acetaldehyde absorbs at wavelengths >290 nm(9) and is susceptible to photodegradation by sunlight in water(8).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), acetaldehyde, which has a vapor pressure of 758 mm Hg at 20 deg C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase acetaldehyde is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 26 hours(SRC), calculated from its rate constant of 1.50X10-11 cu cm/molecule-sec at 25 deg C(3). Acetaldehyde absorbs at wavelengths >290 nm(4) and, therefore, may be susceptible to direct photolysis by sunlight(SRC). The direct photolysis half-life in the atmosphere has reported values of 8.4 hours(5) and 16 hours(6). The direct photolysis half-life at 55 deg N latitude has been calculated as 34 hours in summer and 296 hours in winter(7). The rate constant for the vapor-phase reaction of acetaldehyde with atmospheric nitrate radicals has been measured as 2.62X10-15 cu cm/molecule-sec at 25 deg C(4); this corresponds to an atmospheric half-life of about 12 days(SRC) at an atmospheric concentration of 2.5X10+8 nitrate radicals per cu cm(8). The nitrate radical (NO3) is the dominant atmospheric oxidant during the night-time in most atmospheric environments(9). Monitoring data have shown that acetaldehyde is removed from the air by wet and dry deposition(10).
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