| 환경 거동 | TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 82,000(SRC), determined from a log Kow of 6.50(2) and a regression-derived equation(3), indicates that pentachlorodibenzo-p-dioxin is expected to be immobile in soil(SRC). Volatilization of pentachlorodibenzo-p-dioxin from moist soil surfaces is expected to be an important fate process(SRC) given an estimated Henry's Law constant of 2.2X10-6 atm-cu m/mole(SRC), derived from its vapor pressure, 5.6X10-10 mm Hg(4), and water solubility, 1.2X10-4 mg/l(5). However, adsorption to soil is expected to attenuate volatilization(SRC). Pentachlorodibenzo-p-dioxin is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(4). Pentachlorodibenzo-p-dioxin is susceptible to direct photolysis based on a half-life of 7.6 hr in n-hexadecane solution for 1,2,3,7,8-pentachlorodibenzo-p-dioxin(6). Therefore, some photodegradation may occur on surfaces exposed to sunlight(SRC), although the relative importance of surface photodegradation is unknown(SRC). Biodegradation of pentachlorodibenzo-p-dioxin in soil is expected to be very slow(SRC). 100 percent of pentachlorodibenzo-p-dioxin (as 1,2,3,7,8-pentachlorodibenzo-p-dioxin) applied to a sandy loam soil, at pH 8.1, remained in the soil after a 15 month period(7).AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 82,000(SRC), determined from a log Kow of 6.50(2) and a regression-derived equation(3), indicates that pentachlorodibenzo-p-dioxin 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 2.2X10-6 atm-cu m/mole(SRC), derived from its vapor pressure, 5.60X10-10 mm Hg(4), and water solubility, 1.20X10-4 mg/l(5). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 21 and 236 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 52 years if adsorption is considered(6). According to a classification scheme(7), BCF values of 810(8) and 1,434(9) are high and very high, respectively(SRC). Pentachlorodibenzo-p-dioxin in water is susceptible to direct photolysis in sunlight(9)however, adsorption to sediment and suspended solids may minimize any importance of aquatic photodegradation(SRC). Based on a soil field study(10), biodegradation of pentachlorodibenzo-p-dioxin in water is expected to be very slow(SRC). 100 percent of pentachlorodibenzo-p-dioxin (as 1,2,3,7,8-pentachlorodibenzo-p-dioxin) applied to a sandy loam soil, at pH 8.1, remained in the soil after a 15 month period(10).ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), pentachlorodibenzo-p-dioxin, which has a vapor pressure of 5.60X10-10 mm Hg at 25 °C(2), is expected to exist solely in the particulate phase in the ambient atmosphere(SRC). However, monitoring data suggest that pentachlorodibenzo-p-dioxin will also exist in the vapor-phase in the ambient atmosphere(3). Vapor-phase pentachlorodibenzo-p-dioxin 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 28 days(SRC), calculated from its rate constant of 5.8X10-13 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(4). Particulate-phase pentachlorodibenzo-p-dioxin may be removed from the air by wet and dry deposition(SRC). Particle-bound pentachlorodibenzo-p-dioxin is removed from the atmosphere in rain and has been identified in precipitation samples(5,6). Dry deposition also has been observed(6). Photodegradation of pentachlorodibenzo-p-dioxin bound to fly ash is not an important atmospheric removal mechanism(7). |
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