| 環境中動態 | TERRESTRIAL FATE: Based on a classification scheme(1), Koc values ranging from 79 to 236(2,3) indicate that 1,1,2,2-tetrachloroethane is expected to have high to moderate mobility in soil(SRC). Volatilization of 1,1,2,2-tetrachloroethane from moist soil surfaces is expected to be an important fate process(SRC) given a Henry's Law constant of 4.20X10-4 atm-cu m/mole(4). 1,1,2,2-Tetrachloroethane is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 5.74 mm Hg(5). 1,1,2,2-Tetrachloroethane undergoes biodegradation under anaerobic conditions, but is persistent under aerobic conditions(6). Utilizing the Japanese MITI test, 10% of the Theoretical TOC was reached in 4 weeks(7) indicating that biodegradation is not an important environmental fate process in soil(SRC).AQUATIC FATE: Based on a classification scheme(1), Koc values ranging from 79 to 236(2,3) indicate that 1,1,2,2-tetrachloroethane is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(4) based upon a Henry's Law constant of 4.20X10-4 atm-cu m/mole(5). Using this Henry's Law constant and an estimation method(4), volatilization half-lives for a model river and model lake are 6.5 hours and 6 days, respectively(SRC). According to a classification scheme(6), a BCF range of 4.5 to 13.2(7), suggests the potential for bioconcentration in aquatic organisms is low(SRC). 1,1,2,2-Tetrachloroethane undergoes biodegradation under anaerobic conditions, but is persistent under aerobic conditions(8). Utilizing the river die-away test, 1,1,2,2-tetrachloroethane was biodegraded 19% in 24 days with a 21-day acclimation period(9). 1,1,2,2-Tetrachloroethane undergoes abiotic hydrolysis in water to form trichlorethylene(8,10). The rate of hydrolysis increases with increasing pH(8). At 25 °C, half lives of 36 days to 102 days have been approximated under neutral pH while half lives from 6.6 hours to 1.02 days were determined under alkaline conditions (pH9)(8).AQUATIC FATE: 1,1,2,2-Tetrachloroethane degradation pathways were identified using a field study located along the West Branch Canal Creek at Aberdeen Proving Ground army base in Maryland, situated near the head of the Chesapeake Bay(1). This compound is a common contaminant in groundwater from the area. Groundwater sampling indicated that 1,1,2,2-tetrachloroethane concentrations of 1.5 umoles/L decreased to non-detectable levels within 34 days, forming vinyl chloride and cis- and trans-isomers of 1,2-dichloroethylene, as the groundwater became increasingly reducing along upward flow paths through wetland sediments(1). Degradation experiments carried out in serum bottles whereby 1,1,2,2-tetrachloroethane was reduced by Cr(II), Cu(I), and Fe(0) also resulted in the formation of vinyl chloride and dichloroethylene(2). These studies conclude that both dechloroelimination and hydrogenolysis of 1,1,2,2-tetrachloroethane occur in reducing environments, such as anaerobic wetland sediments(1,2).ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), 1,1,2,2-tetrachloroethane, which has a vapor pressure of 5.74 mm Hg at 25 °C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase 1,1,2,2-tetrachloroethane 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 127 days(SRC), calculated from its rate constant of 1.26X10-13 cu cm/molecule-sec at 25 °C(3). 1,1,2,2-Tetrachloroethane does not contain chromophores that absorb at wavelengths >290 nm and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC). Laboratory experiments have demonstrated that organic vapors in air, including 1,1,2,2-tetrachloroethane, can undergo deposition to snow via adsorption from air to snow(4). |
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