1,1,2,2-Tetrachloroethane

CAS RN:79-34-5

Environmental Fate

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 deg 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 deg 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 deg 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).
Find more information on this substance at: Hazardous Substances Data Bank , TOXNET , PubMed