Page 4: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Trichloroethylene

3.0 Identity, Use and Sources in the Environment

Trichloroethylene (CHCl=CCl2; relative molecular mass 131.4), also known as TCE and trichloroethene, is a colourless liquid with a sweet odour. Its odour thresholds are 546-1092 mg/m³ in air and 0.31 mg/L in water (Amoore and Hautala, 1983; Ruth, 1986). At room temperature, TCE is a volatile, non-viscous liquid with a boiling point of 86.7°C. TCE is moderately soluble in water (1.1-1.4 g/L) and has a low n-octanol/water partition coefficient (log Kow 2.29-2.42), a high vapour pressure (8.0-9.9 kPa at 20-25°C; McNeill, 1979; ATSDR, 1989) and a Henry's law constant of 1.1 kPa·m³/mol at 25°C (Hine and Mookerjee, 1975). In air, 1 ppm is equivalent to 5.41 mg/m³ at 20°C and 101.3 kPa (Verschueren, 1983). Under conditions of normal use, TCE is considered non-flammable and moderately stable, but it requires the addition of stabilizers (up to 2% v/v) in commercial grades.

TCE use has declined sharply in industrialized countries since 1970 (McNeill, 1979). In Canada, 90% of the TCE consumed is used in metal degreasing operations, and the balance is used in miscellaneous applications, including textile solvents, paint removers, coatings and vinyl resins. TCE may also be present in household and consumer products, such as typewriter correction fluids. Production in Canada ceased in 1985; however, TCE is still imported into the country. Over the period 1995-1999, total annual Canadian demand averaged 220 tonnes. More recently, the demand for TCE has decreased. This may be due to several factors, including the use of other solvents for metal degreasing, a decline in the number of companies conducting metal degreasing and an increase in solvent recovery/recycling by users (CPI, 2000). Reporting facilities to Environment Canada's National Pollutant Release Inventory indicated that approximately 17% of TCE was recycled over the period 1996-2000 (Environment Canada, 2000).

Most of the TCE used for degreasing is believed to be emitted to the atmosphere (U.S. EPA, 1985a). TCE may, however, be introduced into surface water and groundwater in industrial effluents (IPCS, 1985). Poor handling as well as improper disposal of TCE in landfills have been the main causes of groundwater contamination. In surface water, volatilization is the principal route of degradation, while photodegradation and hydrolysis play minor roles. In groundwater, TCE is degraded slowly by microorganisms. The biodegradation of another volatile organic pollutant, tetrachloroethylene (or perchloroethylene, PCE), in groundwater may also lead to the formation of TCE (Major et al., 1991).

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