Methanol

CAS RN: 67-56-1

Environmental Fate

TERRESTRIAL FATE: Based on a classification scheme(1), a measured Koc value of 2.75(2) indicates that methanol is expected to have very high mobility in soil(SRC). Volatilization of methanol from moist soil surfaces is expected to be an important fate process(SRC) given a Henry's Law constant of 4.55X10-6 atm-cu m/mole(3). Methanol is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 127 mm Hg(4). Biodegradation half-lives of 1 and 3.2 days measured in a sandy silt loam and sandy loam from Texas and Mississippi, respectively(5), suggest that biodegradation is an important environmental fate process in soil(SRC).
AQUATIC FATE: Based on a classification scheme(1), a measured Koc value of 2.75(2) indicates that methanol 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 4.55X10-6 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 4.6 and 35 days, respectively(SRC). According to a classification scheme(5), a BCF of <10 measured in fish(6) suggests that bioconcentration in aquatic organisms is low(SRC). Methanol lacks functional groups that hydrolyze or absorb light under environmentally relevant conditions(3), therefore hydrolysis and photolysis are not expected to be important environmental fate processes(SRC). Methanol has been shown to undergo rapid biodegradation in a variety of screening studies using sewage seed and activated sludge inoculum(7-10), which suggests that biodegradation is an important environmental fate process in water(SRC).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), methanol, which has a vapor pressure of 127 mm Hg at 25 deg C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase methanol 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 17 days(SRC), calculated from its rate constant of 9.0X10-13 cu cm/molecule-sec at 25 deg C(3). The major degradation product from reaction with hydroxyl radicals is formaldehyde(4).
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