| 環境中動態 | TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 125(SRC), determined from a log Kow of 2.42(2) and a regression-derived equation(3), indicates that isoprene is expected to have high mobility in soil(SRC). Volatilization of isoprene from moist soil surfaces is expected to be an important fate process(SRC) given an estimated Henry's Law constant of 7.7X10-2 atm-cu m/mole(SRC) derived from its vapor pressure, 550 mm Hg(4), and water solubility, 642 mg/L(5). Isoprene is expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(4). A 60% of theoretical BOD using an adapted domestic sewage sludge in the Closed Bottle test and 53-75% of theoretical BOD in 4 weeks using an activated sludge inoculum in the Manometric Respirometry Test(6), suggests that biodegradation is an important environmental fate process in soil(SRC).AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 125(SRC), determined from a log Kow of 2.42(2) and a regression-derived equation(3), indicates that isoprene is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(4) based upon an estimated Henry's Law constant of 7.7X10-2 atm-cu m/mole(SRC) derived from its vapor pressure, 550 mm Hg(5), and water solubility, 642 mg/L(6). Using this Henry's Law constant and an estimation method(4), volatilization half-lives for a model river and model lake are 2.4 hours and 3.3 days, respectively(SRC). According to a classification scheme(7), a BCF range of <5.6-20 measured in carp(8), suggests the potential for bioconcentration in aquatic organisms is low(SRC). A 60% of theoretical BOD using an adapted domestic sewage sludge in the Closed Bottle test and 53-75% of theoretical BOD in 4 weeks using an activated sludge inoculum in the Manometric Respirometry Test(9), suggests that biodegradation is an important environmental fate process in water(SRC).ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), isoprene, which has a vapor pressure of 550 mm Hg at 25 °C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase isoprene 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 3.8 hours(SRC), calculated from its rate constant of 1.01X10-10 cu cm/molecule-sec at 25 °C(3). Isoprene will also be degraded in the atmosphere by reaction with ozone and nitrate radical, the reaction half-lives for these reactions are 19 and 1.2 hours, calculated from reaction rates of 1.43X10-17 cu cm/molecule-sec(4) and 2.4X10+8 nitrate radicals per cu cm(5), respectively. Isoprene absorbs light with a UV maximum of approximately 237 nm(6) and, therefore, is not expected to be susceptible to direct photolysis by sunlight since sunlight consists of wavelengths greater than 290 nm(SRC). |
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