Trimethyl Phosphite (alias of 121-45-9)

CAS RN:121-45-9

Exposure Summary

Trimethyl phosphite's production and use as an intermediate, especially for production of pesticides, may result in its release to the environment through various waste streams. If released to air, a vapor pressure of 24 mm Hg at 25 deg C indicates trimethyl phosphite will exist solely as a vapor in the atmosphere. Vapor-phase trimethyl phosphite 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 33 minutes. Trimethyl phosphite does not absorb at wavelengths >290 nm and therefore is not expected to be susceptible to direct photolysis by sunlight. If released to soil, adsorption to soil, volatilization from moist soil surfaces, and biodegradation are not expected to be important fate processes due to a rapid hydrolysis of trimethyl phosphite. Trimethyl phosphite may volatilize from dry soil surfaces based upon its vapor pressure. If released into water, adsorption to suspended solids and sediment, volatilization from water surfaces, bioconcentration, and biodegradation are not expected to be important fate processes due to the rapid hydrolysis of triethyl phosphite. Trimethyl phosphite hydrolyzes in water to form dimethyl phosphite and methanol. The hydrolysis product, dimethyl phosphite, reached 48% of its theoretical BOD in 4 weeks in the Japanese MITI test indicating it is inherently biodegradable, but not readily biodegradable. The hydrolysis rate of trimethyl phosphite is expected to be similar to the hydrolysis rate of triethyl phosphite. In acid solution (pH = 4) triethyl phosphite hydrolyzes immediately forming diethyl phosphite and ethanol. At pH 7, triethyl phosphite hydrolyzes completely within 20 minutes; after 3 hours 89.3% diethyl phosphite and 10.7% monoethyl phosphite are formed. At pH 9, the half-life of triethyl phosphite in water is approximately 5.1 hours; 70% of the substance remains unhydrolyzed after 3 hours. Occupational exposure to trimethyl phosphite may occur through inhalation and dermal contact with this compound at workplaces where trimethyl phosphite is produced or used. Exposure of the general population to trimethyl phosphite is unlikely since it is used as a chemical intermediate and it is expected to hydrolyze rapidly in the environment. (SRC)
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