Bis(2-ethylhexyl) azelate

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 300,000(SRC), determined from a structure estimation method(2), indicates that di-2-ethylhexyl azelate is expected to be immobile in soil(SRC). Volatilization of di-2-ethylhexyl azelate from moist soil surfaces is expected to be an important fate process(SRC) given an estimated Henry's Law constant of 1.2X10-4 atm-cu m/mole(SRC), using a fragment constant estimation method(3). However, volatilization from moist soil surfaces is expected to be attenuated by adsorption. Di-2-ethylhexyl azelate is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 3.8X10-6 mm Hg(SRC), determined from a fragment constant method(4).

AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 300,000(SRC), determined from an estimation method(2), indicates that di-2-ethylhexyl azelate 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 1.2X10-4 atm-cu m/mole(SRC), developed using a fragment constant estimation method(4). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 22 hours and 17 days, respectively(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column(SRC). The estimated volatilization half-life from a model pond is 27 years, if adsorption is considered(8). Di-2-ethylhexyl azelate is expected to undergo hydrolysis producing 2-ethylhexanol and nonanedioic acid(SRC). An estimated hydrolysis rate constant of 0.07 L/mole-sec corresponds to half-lives of 3.2 years and 120 days at pH values of 7 and 8, respectively(9). According to a classification scheme(5), an estimated BCF of 3.2(SRC), from an estimated log Kow of 9.6(6) and a regression-derived equation(7), suggests the potential for bioconcentration in aquatic organisms is low.

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), di-2-ethylhexyl azelate, which has an estimated vapor pressure of 3.8X10-6 mm Hg at 25 °C(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase di-2-ethylhexyl azelate 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 13 hours(SRC), calculated from its rate constant of 3X10-11 cu cm/molecule-sec at 25 °C(3) determined using a structure estimation method(3). Particulate-phase di-2-ethylhexyl azelate may be removed from the air by wet and dry deposition(SRC). Di-2-ethylhexyl azelate may undergo direct photolysis in the environment, since this compound contains a functional group that can absorb light >290 nm(4).

Using a structure estimation method based on molecular connectivity indices(1), the Koc for di-2-ethylhexyl azelate can be estimated to be 300,000(SRC). According to a classification scheme(2), this estimated Koc value suggests that di-2-ethylhexyl azelate is expected to be immobile in soil.

An estimated BCF of 3.2 was calculated for di-2-ethylhexyl azelate(SRC), using an estimated log Kow of 9.6(1,SRC) and a regression-derived equation(2). According to a classification scheme(3), this BCF suggests the potential for bioconcentration in aquatic organisms is low.

The Henry's Law constant for di-2-ethylhexyl azelate is estimated as 1.2X10-4 atm-cu m/mole(SRC) using a fragment constant estimation method(1). This Henry's Law constant indicates that di-2-ethylhexyl azelate is expected to volatilize from water surfaces(2). Based on this Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1m/sec, wind velocity of 3 m/sec)(2) is estimated as 22 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 17 days(SRC). However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column(SRC). The estimated volatilization half-life from a model pond is 27 years, if adsorption is considered(4). Di-2-ethylhexylazelate's Henry's Law constant(1) indicates that volatilization from moist soil surfaces may occur(SRC), however this process is expected to be attenuated by adsorption. Di-2-ethylhexyl azelate is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 3.8X10-6 mm Hg(SRC), determined from a fragment constant method(3).

The rate constant for the vapor-phase reaction of di-2-ethylhexyl azelate with photochemically-produced hydroxyl radicals has been estimated as 3X10-11 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 13 hours at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). Di-2-ethylhexyl azelate is expected to undergo hydrolysis producing 2-ethylhexanol and nonanedioic acid(SRC). A base-catalyzed second-order hydrolysis rate constant of 0.07 L/mole-sec(SRC) was estimated using a structure estimation method(2); this corresponds to half-lives of 3.2 years and 120 days at pH values of 7 and 8, respectively(2). Di-2-ethylhexyl azelate may undergo direct photolysis in the environment, since this compound contains a functional group that can absorb light >290 nm(3).

NIOSH (NOES Survey 1981-1983) has statistically estimated that 17,011 workers (3,762 of these are female) are potentially exposed to di-2-ethylhexyl azelate in the US(1). Occupational exposure to di-2-ethylhexyl azelate may occur through inhalation and dermal contact with this compound at workplaces where di-2-ethylhexyl azelate is produced or used(SRC).

DRINKING WATER: Di-2-ethylhexyl azelate was detected by GC/MS analysis, but not quantified, in 15 drinking water samples collected from Cincinnati, OH, Miami, FL, New Orleans, LA, Ottumwa, IA, Philadelphia, PA, and Seattle, WA; and also in 16 advanced waste treatment plant samples collected from Escondido, Lake Tahoe, Orange County, and Pomona (all in California), Dallas, TX, and Washington, D.C. (Blue Plains State)(1).

Di-2-ethylhexyl azelate's production and use as a plasticizer for vinyls, a low-temperature plasticizer and also a base for synthetic lubricants may result in its release to the environment through various waste streams. If released to air, an estimated vapor pressure of 3.8X10-6 mm Hg at 25 °C indicates di-2-ethylhexyl azelate will exist in both the vapor and particulate phases. Vapor-phase di-2-ethylhexyl azelate 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 13 hours. Particulate-phase di-2-ethylhexyl azelate will be removed from the atmosphere by wet and dry deposition. Di-2-ethylhexyl azelate may undergo direct photolysis in the environment, since this compound contains a functional group that can absorb light >290 nm. If released to soil, di-2-ethylhexyl azelate is expected to be immobile based upon an estimated Koc of 300,000. Volatilization from moist soil surfaces is expected to be an important fate process based upon an estimated Henry's Law constant of 1.2X10-4 atm-cu m/mole, however this process is expected to be attenuated by adsorption. If released into water, di-2-ethylhexyl azelate is expected to adsorb to suspended solids and sediment in water based upon the estimated Koc. 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 22 hours and 17 days, respectively. However, volatilization from water surfaces is expected to be attenuated by adsorption to suspended solids and sediment in the water column. The estimated volatilization half-life from a model pond is 27 years, if adsorption is considered. Di-2-ethylhexyl azelate is expected to undergo hydrolysis producing 2-ethylhexanol and nonanedioic acid. An estimated hydrolysis rate constant of 0.07 L/mole-sec corresponds to half-lives of 3.2 years and 120 days at pH values of 7 and 8, respectively. An estimated BCF of 3.2 suggests the potential for bioconcentration in aquatic organisms is low. Occupational exposure to di-2-ethylhexyl azelate may occur through inhalation and dermal contact with this compound at workplaces where di-2-ethylhexyl azelate is produced or used. (SRC)