experience notable discomfort, irritation, or certain asymptomatic, nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.

AEGL-2 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.

AEGL-3 is the airborne concentration (expressed as ppm or mg/m3) of a substance above which it is predicted that the general population, including susceptible individuals, could experience life-threatening health effects or death.

Airborne concentrations below the AEGL-1 represent exposure concentrations that could produce mild and progressively increasing but transient and nondisabling odor, taste, and sensory irritation or certain asymptomatic, nonsensory effects. With increasing airborne concentrations above each AEGL, there is a progressive increase in the likelihood of occurrence and the severity of effects described for each corresponding AEGL. Although the AEGL values represent threshold concentrations for the general public, including susceptible subpopulations, such as infants, children, the elderly, persons with asthma, and those with other illnesses, it is recognized that individuals, subject to idiosyncratic responses, could experience the effects described at concentrations below the corresponding AEGL.

SUMMARY

Trimethoxysilane and tetramethoxysilane are colorless liquids with ester-like odors. They are structural analogs and are in the organic silane family. Both chemicals have similar toxicologic effects in the lung and eye. Little relevant data on the toxicity of the chemicals in either humans or laboratory animals are available.

AEGL-1 values were not recommended for trimethoxysilane because of inadequate data. Data were also inadequate to derive AEGL-2 values, so values were derived by taking one-third of the AEGL-3 values. The Standing Operating Procedure for determining AEGL values (NRC 2001) specifies that AEGL-2 values can be derived by this method when a chemical has a steep dose-response curve. AEGL-3 values for trimethoxysilane were determined on the basis of mortality data from 1- and 4-h LC50 (lethal concentration, 50% lethality) inhalation studies in rats (Nachreiner and Dodd 1988). Points of departure were the calculated LC01 (lethal concentration, 1% lethality) values of 263 ppm for 10 min, 123 ppm for 30 min, 76.3 ppm for 1 h, 29.3 ppm for 4 h, and 18.2 ppm for 8 h. A total uncertainty factor of 30 was used. A factor of 3 was applied for interspecies differences, because similar effects were observed in rats, mice, and hamsters exposed at the same concentration in a 5-day inhalation study (Dow Corning Corp. 1981). The default value of 10 was used for intraspecies variabil-



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