Phosgene

CAS RN: 75-44-5

Environmental Fate

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 2.2(SRC), determined from a structure estimation method(2), indicates that phosgene is expected to have very high mobility in soil(SRC). Volatilization of phosgene from moist soil surfaces is expected to be an important fate process(SRC) given a Henry's Law constant of 1.7X10-2 atm-cu m/mole(3). Phosgene is expected to hydrolyze in moist soil; hydrolysis of a 1% solution of phosgene in water is complete within 20 seconds at 0 deg C(4). Phosgene is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 1420 mm Hg(5). Biodegradation data were not available(SRC, 2007).
AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 2.2(SRC), determined from a structure estimation method(2), indicates that phosgene 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 1.7X10-2 atm-cu m/mole(4). Phosgene has been reported to hydrolyze rapidly in seawater(5). Hydrolysis of a 1% solution of phosgene in water is complete within 20 seconds at 0 deg C(6). Measured aqueous phase hydrolysis rate constants for phosgene have ranged from 0.29 to 100 sec-1(7). The rapid hydrolysis suggests that bioconcentration will not be an important environmental fate process(SRC). Biodegradation data were not available(SRC, 2007).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), phosgene, which has a vapor pressure of 1420 mm Hg at 25 deg C(2), is expected to exist solely in the gas phase in the ambient atmosphere. Gas-phase phosgene 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 44 years(SRC), calculated from its rate constant of 1.0X10-15 cu cm/molecule-sec at 25 deg C(3). Phosgene does not absorb UV radiation at wavelengths >290 nm(4) and therefore would not be subject to direct photolysis by sunlight in the troposphere. Phosgene's hydrolytic half-life in the atmosphere, extrapolating from high temperature data, is 113 yr at sea level, assuming 10 torr of water vapor(5).
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