| 환경 거동 | TERRESTRIAL FATE: Based on a classification scheme(1), Koc values ranging from 10,471 to 86,000(2), indicate that permethrin is expected to be immobile in soil(SRC). Volatilization of permethrin from moist soil surfaces is possible(SRC) given an estimated Henry's Law constant of 2.4X10-6 atm-cu m/mole(SRC), derived from its vapor pressure, 5.18X10-8 mm Hg(3), and water solubility, 0.0111 mg/L(3). However, adsorption to soil is expected to attenuate volatilization(SRC). Permethrin is not expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure. Permethrin is susceptible to biodegradation in soil and sediment as demonstrated by incubation studies using sterile and non-sterile conditions(4,5). Degradation in soil and sediments occurs through biodegradation and abiotic hydrolysis(6). Permethrin is susceptible to direct photolysis on soil surfaces exposed to sunlight(3)cis- and trans-permethrin photolysis half-lives of 23.1 and 36.8 days have been measured in water respectively(3). The degradation half-life of permethrin in aerobically incubated soil was less than 4 weeks, and the degradation of the trans-isomer was more rapid than the cis-isomer(7). Faster degradation of the trans-isomers versus the cis-isomers was also observed in soil and sediment studies(8). In two Japanese soils, both the 1R, trans- and 1R, cis-isomers were rapidly degraded under dry conditions with half-lives of less than 2 days(9). Under anaerobic conditions in flooded silt loam soils, degradation half-lives were 32-34 days for 14C-labeled trans-permethrin and greater than 64 days for 14C-labeled cis-permethrin(7). Field dissipation half-lives for permethrin generally fall in the range from 6 to 106 days with 42 days as a selected value for modeling(2). Under aerobic conditions, the field dissipation half-life is roughly 30 days (4-40 day range) and under anaerobic conditions, the field dissipation half-life is roughly 108 days (3-204 day range)(2).AQUATIC FATE: Based on a classification scheme(1), Koc values ranging from 10,471 to 86,000(2), indicate that permethrin is expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is possible(3) based upon an estimated Henry's Law constant of 2.2X10-6 atm-cu m/mole(SRC), derived from its vapor pressure, 5.18X10-8 mm Hg(4), and water solubility, 0.00111 mg/L(4). Using this Henry's Law constant and an estimation method(5), volatilization half-lives for a model river and model lake are 39 days and 289 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 exceeds 100 years if adsorption is considered(6). According to a classification scheme(7), BCF values of approximately 560 and 480 for rainbow trout (Oncorhynchus mykiss) and sheepshead minnow (Cyprinodon vagiegatus), respectively(8,9), suggests the potential for bioconcentration in aquatic organisms is high(SRC). At pH 4, pH 5 and pH 7 (25 °C), permethrin is stable towards abiotic hydrolysis(2,4). At pH 9, the abiotic hydrolysis rate constant is 0.0139 per day at 25 °C(2) which corresponds to a half-life of 50 days(SRC). The hydrolysis half-lives of cis- and trans-permethrin at pH 9(25 °C, sterile water) have been measured as 42.3 and 37.7 days respectively(4). In water, a photolysis rate constant of 0.021 per day has been reported(2) which corresponds to photodegradation half-life of 33 days(SRC). In sterile buffer solutions (pH 4) exposed to irradiation equivalent to natural sunlight (Tokyo, 35 deg N, April-June), cis- and trans-permethrin had photolysis half-lives of 23.1 and 38.6 days respectively(4)using synthetic humic water, the photolysis half-lives decreased to 14.6 and 25.5 days respectively(2). The photolysis half-life of permethrin in seawater exposed to outdoor light was determined to be 14 days(9). Photolysis half-lives of 27.1 and 19.6 hrs were determined for respective cis- and trans-isomers in 800 mL pond water exposed to sunlight(10). Faster photodegradation in humic and natural waters can result from reaction with photo-oxidant species such hydroxyl radicals, peroxy radicals and singlet oxygen(11). Permethrin is susceptible to biodegradation as demonstrated by incubation studies using sterile and non-sterile conditions(9,12). The biodegradation half-life of permethrin in a sediment-seawater solution was less than 2.5 days(9)under sterile conditions there was no significant change in permethrin concentration(9).ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), permethrin, which has a vapor pressure of 5.18X10-8 mm Hg at 25 °C(2), will exist in both the vapor and particulate phases in the ambient atmosphere(SRC). Vapor-phase permethrin is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals and ozone(SRC)the half-life for reaction with hydroxyl radicals in air is estimated to be 17 hours(SRC), calculated from its rate constant of 2.3X10-11 cu cm/molecule-sec at 25 °C(3)the half-life for reaction with ozone in air is estimated to be 49 days(SRC), calculated from its rate constant of 2.3X10-19 cu cm/molecule-sec at 25 °C(3). Particulate-phase permethrin may be removed from the air by wet and dry deposition(SRC). Permethrin absorbs light in the environmental spectrum(4) and has been shown to photodegrade in sunlight(2)therefore, permethrin can degrade through direct photolysis(SRC). |
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