Methanol

CAS RN: 67-56-1

Exposure Summary

Methanol's production and use as a solvent, fuel additive, and in the production of formaldehyde, acetic acid, and methyl tertiary butyl ether (MTBE) may result in its release to the environment through various waste streams. Its use in hydraulic fracturing fluids will result in its direct release to the environment. It can also be released directly to the environment in exhaust gases from combustion engines. Methanol has been identified as a natural emission product from various plants and as a biological decomposition product of biological wastes and sewage; natural emission sources include volcanic gases, vegetation, microbes, and insects, and methanol is a product of decaying organic material. If released to the atmosphere, a vapor pressure of 127 mm Hg at 25 deg C indicates that methanol will exist solely in the vapor phase. Vapor phase methanol is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 17 days. If released to soil, methanol is expected to have very high mobility based upon a measured Koc of 2.75. Volatilization from moist soil surfaces is expected to be an important fate process based upon a Henry's Law constant of 4.55X10-6 atm-cu m/mole. Methanol may also volatilize from dry soils based upon its vapor pressure. Biodegradation half-lives of 1 and 3.2 days measured in a sandy silt loam and sandy loam from Texas and Mississippi, respectively, suggest that biodegradation is an important environmental fate process in soil. If released into water, methanol is not expected to adsorb to suspended solids and sediment based upon the Koc. 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 4.6 and 35 days, respectively. Rapid biodegradation in a variety of screening studies using sewage seed and activated sludge inoculum suggests that biodegradation is an important environmental fate process in water. BCF values of less than 10 in fish suggest that bioconcentration in aquatic organisms is low. Hydrolysis and photolysis are not expected to be an important environmental fate processes since this compound lacks functional groups that hydrolyze and photolyze under environmental conditions. Occupational exposure to methanol may occur through inhalation and dermal contact with this compound at workplaces where methanol is produced or used. Monitoring data indicate that the general population may be exposed to methanol via inhalation of ambient air, and ingestion of food and drinking water. Exposure to methanol can occur when people use certain paint strippers, aerosol spray paints, wall paints, windshield wiper fluid, and small engine fuel. (SRC)
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