2,7-디메틸피렌

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 140,000(SRC), determined from a structure estimation method(2), indicates that 2,7-dimethylpyrene is expected to be immobile in soil(SRC). Volatilization of 2,7-dimethylpyrene from moist soil surfaces may occur given an estimated Henry's Law constant of 3.4X10-6 atm-cu m/mole(SRC), using a fragment constant estimation method(2). However, adsorption to soil is expected to attenuate volatilization(SRC). 2,7-Dimethylpyrene is not expected to volatilize from dry soil surfaces(SRC) based upon an estimated vapor pressure of 6.9X10-8 mm Hg at 25 °C(SRC), determined from a fragment constant method(2). PAHs with four or more rings, such as 2,7-dimethylpyrene, are generally expected to be resistant to biodegradation(3). By analogy to pyrene, biodegradation is expected to occur slowly in soils, with estimated half-lives ranging from several weeks to years(4,5). Faster biodegradation rates occur with exposure to acclimated microbes(6). Degradation of analogous 1-methylpyrene during a bioslurry method reached 38% after 29 days of incubation using a contaminated soil from a former gasworks(7). By analogy to pyrene which absorbs strongly at wavelengths >290 nm(8), 2,7-dimethylpyrene is expected to be susceptible to direct photolysis on surfaces exposed to sunlight(SRC).

AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 140,000(SRC), determined from a structure estimation method(2), indicates that 2,7-dimethylpyrene is expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(3) based upon an estimated Henry's Law constant of 3.4X10-6 atm-cu m/mole(SRC), developed using a fragment constant estimation method(2). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 17 and 126 days, respectively(SRC). 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 >10 years if adsorption is considered(4). According to a classification scheme(5), an estimated BCF of 4400(SRC), from an estimated log Kow of 6.03(2) and a regression-derived equation(2), suggests the potential for bioconcentration in aquatic organisms is very high, provided the compound is not metabolized by the organism(SRC). However, 2,7-dimethylpyrene may not bioconcentrate in aquatic organisms which contain microsomal oxidase, such as some fish, as this enzyme enables the rapid metabolism of certain polycyclic aromatic hydrocarbons(6). A measured fish biotransformation half-life of 2.08 days has been reported for the analogous pyrene(7). The near surface half-life for direct photolysis of analogous pyrene in water by sunlight was measured as 0.68 hours(8) and 0.85 hours(9). PAHs with four or more rings, such as 2,7-dimethylpyrene, are generally expected to be resistant to biodegradation(10). By analogy to pyrene, biodegradation is expected to occur slowly in soils, with estimated half-lives ranging from several weeks to years(11,12). Faster biodegradation rates occur with exposure to acclimated microbes(13). Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions(3).

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), 2,7-dimethylpyrene, which has an estimated vapor pressure of 6.9X10-8 mm Hg at 25 °C(SRC), determined from a fragment constant method(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase 2,7-dimethylpyrene 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 2.4 hours(SRC), calculated from its rate constant of 1.6X10-10 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(2). Particulate-phase 2,7-dimethylpyrene may be removed from the air by wet and dry deposition(SRC). By analogy to pyrene which absorbs strongly at wavelengths >290 nm(3,4), 2,7-dimethylpyrene is expected to be susceptible to direct photolysis by sunlight(SRC).

Using a structure estimation method based on molecular connectivity indices(1), the Koc of 2,7-dimethylpyrene can be estimated to be 140,000(SRC). According to a classification scheme(2), this estimated Koc value suggests that 2,7-methylpyrene is expected to be immobile in soil.

Polycyclic aromatic hydrocarbons (PAHs), such as methylpyrenes, occur as ubiquitous products of incomplete combustion of fossil fuels, wood, diesel oils and gasoline fuels(1). 2,7-Dimethylpyrene's occurrence in gasoline and diesel exhaust(2) will release the compound directly to the environment(SRC). Methylpyrenes occur in tobacco smoke(2,3).

AEROBIC: Polycyclyic aromatic hydrocarbons (PAHs) with four or more rings, such as 2,7-dimethylpyrene, are generally expected to be resistant to biodegradation(1). Biodegradation of the analogous compound pyrene is expected to occur slowly in soils, with estimated half-lives ranging from several weeks to years(2,3). Faster biodegradation rates occur with exposure to acclimated microbes(4). Soil microcosm studies using three industrial soils from Austria found pronounced biodegradation of pyrene in one soil (about 65-75% over 65 days of incubation), but only slight biodegradation in the other two soils(5). Using a pilot-scale bioslurry treatment method with contaminated soil from a former gasworks site, the fraction of initial 1-methylpyrene (analogous compound) remaining in the soil after 7, 24 and 29 days of incubation was 100, 85 and 62% respectively(6).

An estimated BCF of 4400 was calculated in fish for 2,7-dimethylpyrene(SRC), using an estimated log Kow of 6.03(1) and a regression-derived equation(1). According to a classification scheme(2), this BCF suggests the potential for bioconcentration in aquatic organisms is very high(SRC), provided the compound is not metabolized by the organism(SRC). However, 2,7-dimethylpyrene may not bioconcentrate in aquatic organisms which contain microsomal oxidase, such as fish, as this enzyme enables the rapid metabolism of certain polycyclic aromatic hydrocarbons(3). A measured fish biotransformation half-life of 2.08 days has been reported for the analogous compound pyrene(4).

The Henry's Law constant for 2,7-dimethylpyrene is estimated as 3.4X10-6 atm-cu m/mole(SRC) using a fragment constant estimation method(1). This value indicates that 2,7-dimethylpyrene is expected to volatilize from water surfaces(2). Based on this Henry's Law constant, the estimated 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 17 days(SRC). The estimated 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 126 days(SRC). 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 (2 m deep, 1 cm active benthic subsystem of bulk density 1.75 g/cc, wind velocity of 1.5 m/sec) is >10 years if adsorption is considered and 170 days if adsorption is ignored(3). 2,7-Dimethylpyrene's Henry's Law constant indicates that volatilization from moist soil surfaces may occur(SRC). 2,7-Dimethylpyrene is not expected to volatilize from dry soil surfaces based on an estimated vapor pressure of 6.9X10-8 mm Hg(SRC), determined from a fragment constant method(1).

The rate constant for the vapor-phase reaction of 2,7-dimethylpyrene with photochemically-produced hydroxyl radicals has been estimated as 1.6X10-10 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 2.4 hours at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). Methylpyrenes have practically identical UV absorption spectra as pyrene(2). Pyrene (analogous compound) absorbs strongly at wavelengths >290 nm(3,4) and, therefore, 2,7-dimethylpyrene is expected to be susceptible to direct photolysis by sunlight(SRC). Approximately 6% photolytic degradation occurred when pyrene was adsorbed to a fly ash substrate and exposed to natural sunlight for 5 hours(5). The near surface half-life for direct photolysis of pyrene in water by sunlight was measured as 0.68 hours(6) and 0.85 hours(7). The photolysis half-life of pyrene on spruce needle surfaces exposed to full sunlight in Munich, Germany in July 2001 was 37 hours(8). 2,7-Dimethylpyrene is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(9).

Occupational exposure to 2,7-dimethylpyrene may occur through inhalation and dermal contact with this compound at workplaces where 2,7-dimethylpyrene is produced as a product of incomplete combustion of fossil fuels. The general population may be exposed to 2,7-dimethylpyrene via inhalation of ambient air contaminated from combustion emissions, inhalation of tobacco smoke and dermal contact with particulate matter resulting from combustion(SRC). Occupational and general population exposure to PAHs, such as 2,7-dimethylpyrene, generally occurs as a mixture(1). PAHs, such as methylpyrenes, can occur in foods that are char-broiled(1) or smoked(2).

Toxic pollutant designated pursuant to section 307(a)(1) of the Federal Water Pollution Control Act and is subject to effluent limitations. /Polynuclear aromatic hydrocarbons (including benzanthracenes, benzopyrenes, benzofluoranthene, chrysenes, dibenz-anthracenes, and indenopyrenes)/

For the maximum protection of human health from the potential carcinogenic effects of exposure to polynuclear aromatic hydrocarbons through ingestion of contaminated water and contaminated aquatic organisms, the ambient water concentration should be zero, based on the nonthreshold assumption for this chemical. However, zero level may not be attainable at the present time. Therefore, the levels which may result in incremental increase of cancer risk over the lifetime are estimated at 1X10-5, 1X10-6, and 1X10-7. The corresponding recommended criteria are 28.0 ng/L, 2.8 ng/L, and 0.28 ng/L, respectively. If these estimates are made for consumption of aquatic organisms only, excluding consumption of water, the levels are 311.0 ng/L, 31.1 ng/L, and 3.11 ng/L, respectively. /Polynuclear aromatic hydrocarbons/.