Page 5: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Carbon Tetrachloride

Part II. Science and Technical Considerations

4.0 Identity, use, and sources in the environment

4.1 Identity and uses

Carbon tetrachloride (CCl4; relative molecular mass 153.82), also known as tetrachloromethane, is a colourless, nonflammable, heavy liquid with a sweet, aromatic, non-irritating odour (IPCS, 1999; Lide, 2005-2006). At room temperature, carbon tetrachloride is a volatile liquid with a boiling point of 76.5°C (ATSDR, 2005). Its odour thresholds are <64 mg/m³ in air and 0.52 mg/L in water (Amoore and Hautala, 1983). It is a chlorinated solvent that is miscible with organic solvents, but it has poor solubility in water (800 mg/L at 20°C) (ATSDR, 2005).

Carbon tetrachloride has an n-octanol/water partition coefficient (log Kow) of 2.64, a high vapour pressure (12.2 kPa at 20°C; 15.36 kPa at 25°C), and high volatilization from water (Henry's law constant of 2.98 kPa·m³/mol at 25°C) (IPCS, 1999; WHO, 2004a). Carbon tetrachloride is considered one of several ozone-depleting substances (UNEP, 1994, 2002). An international agreement, the Montreal Protocol on Substances that Deplete the Ozone Layer, was reached in 1987 to control the production and consumption of certain ozonedepleting substances, including carbon tetrachloride. In Canada, carbon tetrachloride was phased out (100% elimination) in 1996 (Environment Canada, 2006a). However, it can still be imported for limited use as a feedstock in chemical production (CCME, 1999, 2001). According to Environment Canada (2006b), all other uses of carbon tetrachloride are prohibited in Canada. In the United States, although carbon tetrachloride is still manufactured, it has seen a decline in the amounts imported and exported (ATSDR, 2005).

In the past, carbon tetrachloride was used mainly as a feedstock for the production of chlorofluorocarbons (for refrigerant use). Because of its solvent properties, carbon tetrachloride was also used as a component of domestic cleaning fluids and as a degreaser in industry, while its non-flammable properties led to its past use in fire extinguishers. It was also used as a solvent for oils, fats, lacquers, varnishes, rubber waxes, and resins, as a grain fumigant, and as a dry cleaning agent, as well as in pharmaceutical products (ATSDR, 2005).

4.2 Environmental sources and fate

Most atmospheric carbon tetrachloride is a result of direct releases to the atmosphere (ATSDR, 2005). In the lower atmosphere (the troposphere), carbon tetrachloride is fairly stable and resists breakdown. As it diffuses to higher altitudes (the stratosphere, more than 20 km above the Earth's surface), it has been shown to undergo photodegradation in the presence of strong ultraviolet light (short wavelengths, 185-225 nm) to produce chlorine atoms and other chlorine species, which deplete ozone. According to estimates, the atmospheric lifetime (troposphere and stratosphere combined) of carbon tetrachloride ranges from 30 to 100 years, with 50 years as a reasonable average (ATSDR, 2005).

Carbon tetrachloride can be found in surface water as a result of industrial activities or from rainfall. In surface waters, volatilization is the principal route of loss, whereas no measurable degradation was seen as a result of photolysis, oxidation, or hydrolysis (Howard, 1990; CCME, 1999; ATSDR, 2005). Limited studies have shown that biodegradation occurs in the laboratory under both anaerobic and aerobic conditions (Howard, 1990). Despite its n-octanol/water partition coefficient of 2.64, bioaccumulation in fish is not expected to be significant because of its short tissue lifetime in some species (IPCS, 1999).

Most of the carbon tetrachloride released into soil as a result of spills, runoff, or leaching will rapidly volatilize and thus will be present in the air (IPCS, 1999). Experimental studies showed a short half-life (5 days using silt loam and sandy loam) in both sterile and non-sterile soils (Anderson et al., 1991). Based on its soil adsorption coefficient (Koc of 71), carbon tetrachloride is not expected to bind significantly to soil and therefore should move readily through soil (IPCS, 1999; OEHHA, 2000; ATSDR, 2005). As a result, carbon tetrachloride may leach from soil into groundwater (Letkiewicz et al., 1983).

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