Methyl Isocyanate

CAS RN: 624-83-9

Exposure Summary

Methyl isocyanate's production and use as a chemical intermediate and in the manufacture of carbamate-based and urea-based insecticides and fungicides may result in its release to the environment through various waste streams. If released to air, a vapor pressure of 348 mm Hg at 20 deg C indicates methyl isocyanate will exist solely as a vapor in the atmosphere. Vapor-phase methyl isocyanate 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 118 days. Methyl isocyanate does not contain chromophores that absorb at wavelengths >290 nm and therefore is not expected to be susceptible to direct photolysis by sunlight. Hydrolysis is expected to be the dominant fate process for methyl isocyanate in soil and water based upon half-lives of 20 and 9 min at 15 and 25 deg C, respectively, calculated from measured aqueous hydrolysis rate constants. If released to soil, adsorption, biodegradation, and volatilization from moist soil surfaces are not expected to compete with hydrolysis as important fate processes; however, methyl isocyanate may volatilize from dry soil surfaces based upon its vapor pressure. If released to water, adsorption to sediment, bioconcentration, biodegradation, and volatilization from water surfaces are not expected to compete with hydrolysis as important fate processes. The products of hydrolysis may include N-carboxymethylamine, methylamine, carbon dioxide, and N,N'-dimethylurea. Occupational exposure to methyl isocyanate may occur through inhalation and dermal contact with this compound at workplaces where methyl isocyanate is produced or used. The general population may be exposed to methyl isocyanate through inhalation of cigarette smoke. (SRC)
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