Isobutyl Stearate

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 33,000(SRC), determined from a structure estimation method(2), indicates that isobutyl stearate is expected to be immobile in soil(SRC). Volatilization of isobutyl stearate from moist soil surfaces is expected to be an important fate process(SRC) given an estimated Henry's Law constant of 0.038 atm-cu m/mole(SRC), using a fragment constant estimation method(3). However, adsorption to soil is expected to attenuate volatilization(SRC). Isobutyl stearate is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 2.8X10-5 mm Hg(4). Isobutyl stearate is expected to rapidly biodegrade in aerobic soils as suggested by the rapid biodegradation of structurally similar long-chain fatty acid esters(5-7).

AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 33,000(SRC), determined from a structure estimation method(2), indicates that isobutyl stearate is expected to adsorb to suspended solids and sediment in water(SRC). Volatilization from water surfaces is expected(3) based upon an estimated Henry's Law constant of 0.038 atm-cu m/mole(SRC), developed using a fragment constant estimation method(4). Volatilization half-lives for a model river and model lake are 5 hours and 7 days, respectively(SRC), using an estimation method(3). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column(SRC). The volatilization half-life from a model pond is estimated to be about 64 hours ignoring adsorption; when considering maximum adsorption the volatilization half-life increases to 10 months(5). According to a classification scheme(6), an estimated BCF of 3(SRC) from an estimated log Kow of 9.63(12) and a regression-derived equation(7), suggests the potential for bioconcentration in aquatic organisms is low. Isobutyl stearate is expected to rapidly biodegrade in aerobic soils as suggested by the rapid biodegradation of structurally similar long-chain fatty acid esters(8-10). An estimated base-catalyzed second-order hydrolysis rate constant of 0.015 L/mole-sec(11,SRC) corresponds to half-lives of 14 and 1.4 years at pH values of 7 and 8, respectively(11).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), isobutyl stearate, which has an estimated vapor pressure of 2/8X10-5 mm Hg at 25 °C(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase isobutyl stearate 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 15 hours(SRC) from its estimated rate constant of 2.6X10-11 cu cm/molecule-sec at 25 °C(SRC) using a structure/reactivity estimation method(3). Particulate-phase isobutyl stearate may be removed from the air by wet and dry deposition(SRC).

The CIR Expert Panel concluded that the alkyl esters, listed subsequently, are safe in the present practices of use and concentration described in this safety assessment when formulated to be non-irritating.

Safe for use in cosmetics, with qualifications

Using a structure estimation method based on molecular connectivity indices(1), the Koc for isobutyl stearate can be estimated to be about 33,000(SRC). According to a classification scheme(2), this estimated Koc value suggests that isobutyl stearate is expected to be immobile in soil.

RURAL/REMOTE: Isobutyl stearate was qualitatively detected in a single sample obtained at a countryside apartment in Schmallenberg, Germany, 1988(1).

INDOOR AIR: Isobutyl stearate was qualitatively detected in the emissions from new carpeting(1).

An estimated BCF of 3 was calculated for isobutyl stearate(SRC) using an estimated log Kow of 9.63(1,SRC) and a regression-derived equation(2). According to a classification scheme(3), the estimated BCF suggests the potential for bioconcentration in aquatic organisms is low.

The Henry's Law constant for isobutyl stearate is estimated as 0.038 atm-cu m/mole(SRC) using a fragment constant estimation method(1). This Henry's Law constant indicates that isobutyl stearate is expected to volatilize rapidly from water surfaces(2). Based on this Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1 m/sec, wind velocity of 3 m/sec)(2) is estimated as approximately 5 hours(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(2) is estimated as approximately 7 days(SRC). Isobutyl stearate's Henry's Law constant(1) indicates that volatilization from moist soil surfaces may occur(SRC). The volatilization half-life from a model pond 2 m deep is estimated to be about 64 hours ignoring adsorption; when considering maximum adsorption the volatilization half-life increases to 10 months(3). Isobutyl stearate's Henry's Law constant(1) indicates that volatilization from moist soil surfaces may occur(SRC). Isobutyl stearate is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 2.8X10-5 mm Hg(4).

The rate constant for the vapor-phase reaction of isobutyl stearate with photochemically-produced hydroxyl radicals has been estimated as 2.6X10-11 cu cm/molecule-sec at 25 °C(SRC) using a structure/reactivity estimation method(1). This corresponds to an atmospheric half-life of about 15 hours at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). A base-catalyzed second-order hydrolysis rate constant of 0.016 L/mole-sec(SRC) was estimated using a structure estimation method(2); this corresponds to half-lives of 14 and 1.4 years at pH values of 7 and 8, respectively(2). Isobutyl stearate is not expected to directly photolyze due to the lack of absorption in the environmental UV spectrum.

NIOSH (NOES Survey 1981-1983) has statistically estimated that 8,524 workers (1,325 of these are female) are potentially exposed to isobutyl stearate in the US(1). Occupational exposure to isobutyl stearate may occur through inhalation and dermal contact with this compound at workplaces where isobutyl stearate is produced or used(SRC). The general population may be exposed to isobutyl stearate due to its presence in cosmetics, inks, coatings, polishes, soaps, and other consumer products(2,3).

Isobutyl stearate's production and use in a variety of consumer products and cosmetics may result in its release to the environment through various waste streams. If released to air, an estimated vapor pressure of 2.8X10-5 mm Hg at 25 °C indicates isobutyl stearate will exist in the vapor phase in the ambient atmosphere. Vapor-phase isobutyl stearate 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 15 hours. If released to soil, isobutyl stearate is expected to have no mobility based upon an estimated Koc of 33,000. Volatilization from moist soil surfaces is expected to be an important fate process based upon an estimated Henry's Law constant of 0.038 atm-cu m/mole. However, adsorption to soil is expected to attenuate volatilization. Isobutyl stearate is expected to rapidly biodegrade in aerobic soils as suggested by the rapid biodegradation of structurally similar long-chain fatty acid esters. If released into water, isobutyl stearate is expected to adsorb to suspended solids and sediment in the water column based upon the estimated Koc. Isobutyl stearate is expected to rapidly biodegrade in aerobic waters. Volatilization from water surfaces is expected to be an important fate process based upon this compound's estimated Henry's Law constant. Estimated volatilization half-lives for a model river and model lake are 5 hours and 7 days, respectively. However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column. The volatilization half-life from a model pond is estimated to be about 64 hours ignoring adsorption; when considering maximum adsorption the volatilization half-life increases to 10 months. An estimated BCF of 3 suggests the potential for bioconcentration in aquatic organisms is low. An estimated base-catalyzed second-order hydrolysis rate constant of 0.015 L/mole-sec corresponds to half-lives of 14 and 1.4 years at pH values of 7 and 8, respectively. Occupational exposure to isobutyl stearate may occur through inhalation and dermal contact with this compound at workplaces where isobutyl stearate is produced or used. The general population may be exposed to isobutyl stearate due to its presence in cosmetics and other consumer products. (SRC)