Guidelines for Canadian Drinking Water Quality: Supporting Documentation - Trichloroethylene

1.0 Guideline

The maximum acceptable concentration (MAC) for trichloroethylene in drinking water is 0.005 mg/L (5 µg/L).

2.0 Executive Summary

Trichloroethylene (TCE) is a volatile solvent that is used extensively in the automotive and metals industries for vapour degreasing and cold cleaning of metal parts. TCE is not manufactured in Canada, and its use is regulated under the Canadian Environmental Protection Act, 1999. Canadians can be exposed to TCE through its presence in drinking water, air and food. Certain segments of the population could be exposed via contaminated soil or occupational settings.

This supporting document focuses on the health risks associated with TCE in drinking water, including multiple routes of exposure -- ingestion as well as inhalation and skin absorption from showering and bathing. It assesses all identified health risks, taking into account new studies and approaches, and incorporates appropriate safety factors. The guideline of 0.005 mg/L will protect humans from both cancer and non-cancer health risks.

2.1 Health Effects

Animal studies have shown links between exposure to TCE and kidney and testicular tumours in rats and pulmonary and liver tumours in mice. Studies in humans seem to support these links, but further studies are needed to confirm them, in part because other chemicals were also present. Based on the evidence from both animal and human studies, TCE has been classified as probably carcinogenic to humans. Research is ongoing in this area.

Animal and human studies have shown a small increase in the rate of reproductive effects (heart malformations in fetuses) above what can be expected under normal circumstances. The data from the human studies came from people who had been exposed to very high levels of TCE and other solvents through contaminated groundwater. Further studies are required to confirm these developmental effects as well as their long-term significance to human health.

2.2 Exposure

TCE evaporates readily from surface water but may occasionally be found in groundwater. TCE is not a concern for the majority of Canadians who rely on surface water as their source of drinking water. TCE is not a widespread problem in Canada, affecting only some groundwater supplies; where TCE is detected in Canadian drinking water supplies, levels are generally less than 0.001 mg/L. TCE can be introduced into groundwater as a result of industrial effluents or spills or leaking from old dump sites.

2.3 Treatment

Options to reduce exposure to TCE include finding an alternative source of drinking water; enhancing treatment to reduce the level of TCE in the drinking water to below the proposed guideline in municipal systems relying on groundwater supplies; and using drinking water treatment devices where individual households obtain drinking water from private wells. Health Canada recommends that consumers use certified treatment devices. Point-of-entry systems are preferred for volatile organic compounds (VOCs) such as TCE because they reduce exposure through inhalation and dermal absorption by providing treated water for bathing and showering. Although certified point-of-use treatment devices are currently available for the reduction of VOCs, including TCE, certified point-of-entry treatment devices cannot be purchased off the shelf; however, systems can be designed and constructed with certified materials.

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 K_ow 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).

4.0 Exposure

Canadians can be exposed to TCE through its presence in drinking water, air and food. In addition, certain segments of the population can be exposed via contaminated soil, through the use of specific consumer products or in occupational settings. Since TCE has been detected in human milk, nursing infants could potentially be exposed (U.S. EPA, 2001b). Although some exposure data are available, they are considered insufficient to justify modifying the default allocation factor for drinking water of 20%.

4.1 Water

TCE has been detected frequently in natural water and drinking water in Canada and other countries. Due to its high volatility, TCE concentrations are normally low in surface water (≤1 µg/L). However, in groundwater systems where volatilization and biodegradation are limited, concentrations may be higher if contamination has occurred in the vicinity and leaching has taken place.

Because analytical methods have improved over the years since TCE was first assayed, concentrations that were once considered "non-detectable" are now quantifiable. This confounds the use of historical TCE data, as the values for "non-detectable" have changed over time.

TCE was detected in raw and treated water at 10 potable water supply facilities in Ontario in 1983 at levels ranging from ≤0.1 to 0.8 µg/L (Mann Testing Laboratories Ltd., 1983). In 1979, TCE was found in over half of potable water samples taken at 30 treatment facilities across Canada; mean concentrations were 1 µg/L or less, and the maximum level was 9 µg/L (Otson et al., 1982).

Monitoring data from eight Canadian provinces for the period 1985-1990 indicated that 95% of 7902 samples from drinking water supplies (raw, treated or distributed water) had TCE concentrations below 1 µg/L. The maximum concentration was 23.9 µg/L (groundwater sample). Most (75%) of the samples in which TCE was detected were from groundwater sources (Department of National Health and Welfare, 1993). More recent data from New Brunswick (1994-2001), Alberta (1998-2001), the Yukon (2002), Ontario (1996-2001) and Quebec (1985-2002) for raw (surface water and groundwater), treated and distributed water indicated that more than 99% of samples contained TCE at concentrations less than or equal to 1.0 µg/L. The maximum concentration was 81 µg/L. Of those samples with detectable TCE concentrations, most were from groundwater (Alberta Department of Environmental Protection, 2002; New Brunswick Department of Health and Wellness, 2002; Ontario Ministry of Environment and Energy, 2002; Yukon Department of Health and Social Services, 2002; Ministère de l'Environnement du Québec, 2003).

A 2000 survey of 68 First Nations community water supplies (groundwater and surface water) in Manitoba found that TCE concentrations were non-detectable (<0.5 µg/L) (Yuen and Zimmer, 2001).

Groundwater is the sole source of water for an estimated 25-30% of the Canadian population (Statistics Canada, 1994). In 1995, a national review of TCE occurrence data was carried out to determine the extent of groundwater contamination by TCE and the number of people potentially exposed to contaminated drinking water. The majority of sites were from Ontario and New Brunswick. The review was based on urban groundwater supplies. Of the 481 municipal/communal and 215 private/domestic groundwater supplies (raw water), 8.3% and 3.3%, respectively, contained TCE, at average maximum concentrations of 25 µg/L and 1680 µg/L, respectively. This review involved a compilation of data from a variety of sources over different periods of time. Consequently, interpretation of the data is made more difficult by the range of detection limits. A majority of all sites (93%) had non-detectable levels (<0.01-10 µg/L), 3.6% had a maximum concentration of <1 µg/L, 1.4% had a maximum of 1-10 µg/L, 0.43% had a maximum of 10-100 µg/L and 1.3%* had a maximum of >100 µg/L (Raven and Beck Environmental Ltd., 1995).

It was estimated that approximately 1.67 million of the 7.1 million Canadians who relied on groundwater for household use in 1995 were covered by this study. Of the 1.67 million surveyed, the water supplies of 49% had non-detectable levels of TCE (<0.01-10 µg/L), 48.1% had a maximum of 1-10 µg/L, 2.1% had a maximum of 10-100 µg/L and 0.8% had a maximum of >100 µg/L. Despite the problems associated with the wide range of detection limits reported in this study, the results of the survey suggested that more than 95% of Canadians who rely on groundwater are exposed to less than 10 µg TCE/L in their drinking water. In fact, this probably represents a worst-case scenario, since the sampled data were for raw water and may not be representative of water received at households (Raven and Beck Environmental Ltd., 1995).

4.2 Multi-route Exposure through Drinking Water

Due to TCE's volatility and lipid solubility, exposure can also occur dermally and through inhalation, especially through bathing and showering. For the purposes of assessing overall TCE exposure, the relative contribution of each exposure route needs to be assessed. These contributions are expressed in litre equivalents per day (Leq/day). For example, an inhalation exposure of 1.7 Leq/day means that the daily exposure to TCE via inhalation is equivalent to a person drinking an extra 1.7 L of water per day.

Bogen et al. (1988) accounted for oral, dermal and inhalation routes of exposure to TCE from household uses of tap water. They proposed lifetime Leq/day values for 70-kg adults of 2.2 (ingestion), 2.9 (inhalation) and 2 (dermal). The ingestion value was based on the consideration of U.S. age-specific consumption rates, and the dermal number was derived using a generic dermal absorption coefficient value for VOCs, rather than a TCE-specific value. In addition to the shower scenario, these authors quantified exposure via household air when determining the Leq/day value for the inhalation route.

Weisel and Jo (1996) concluded that the dermal and inhalation routes contribute internal doses similar to that from ingestion of tap water and that their total contribution is greater than that from ingestion. However, in the absence of data for route-specific doses and the TCE concentration in air, a verification of their conclusions and the determination of Leq/day values for the various routes are not easily achieved.

Lindstrom and Pleil (1996) outlined simple methodological approaches for the calculation of potential doses received by the ingestion, dermal and inhalation routes. Using a water concentration of 4.4 µg/L, these authors calculated that the ingested dose was more important than the inhaled dose for a 10-minute shower, which in turn was greater than the dermal dose.

Krishnan (2003) determined Leq/day values for dermal and inhalation exposures of adults and children (6-, 10- and 14-year-olds) to TCE (5 µg/L) in drinking water for a 10-minute shower and a 30-minute bath on the basis of the methodological approach of Lindstrom and Pleil (1996), the use of physiologically based pharmacokinetic (PBPK) models and consideration of the fraction absorbed (Laparé et al., 1995; Lindstrom and Pleil, 1996; Poet et al., 2000). The "fraction absorbed" for the dermal and inhalation exposures took into consideration the TCE dose that was absorbed following exposure as well as that portion that was excreted in the following 24 hours. It was assumed that 100% of the skin is exposed in both the shower and bath scenarios, and a dermal absorption coefficient specific to TCE was used (Nakai et al., 1999). Complete (100%) absorption of ingested drinking water was assumed for all subpopulations; this was supported by the extent of hepatic extraction of TCE (Laparé et al., 1995).

Leq/day values for the inhalation and dermal routes were higher for the 30-minute bath scenario than for the 10-minute shower for all subpopulations based on the longer exposure time. The highest value was 3.9 Leq/day (1.5 L ingestion, 1.7 L inhalation, 0.7 L dermal) for adults. The 3.9 Leq/day value (which can be rounded to 4.0 Leq/day) is considered to be conservative, since most Canadians do not take a 30-minute bath on a daily basis. In the event that individuals spend more than 10 minutes in a shower or are exposed to TCE via other household activities, the calculated 4.0 Leq/day value (which includes inhalation and dermal exposure from a 30-minute bath) should be adequate.

4.3 Air

Studies conducted in the 1980's and 1990's have detected TCE in outdoor and indoor air in Canada. Levels of TCE in air were determined in Toronto and Montreal for 1 year (1984-1985) and in Sarnia and Vancouver for 1 month (autumn 1983). Mean levels for the four cities were 1.9, 0.7, 1.2 and 1.0 µg/m³, respectively, with maxima of 8.6, 1.7, 3.6 and 3.4 µg/m³, respectively (Environment Canada, 1986). In another survey, mean concentrations of TCE in ambient air at 11 urban sites and 1 rural site in Canada (1988-1990) ranged from 0.07 to 0.45 µg/m³ (Vancouver and Calgary, respectively), with an overall mean value of 0.28 µg/m³ and a maximum single value of 19.98 µg/m³ reported in Montreal (Dann, 1993).

More recent U.S. data are similar to the levels measured in Canada. In 1998, ambient air measurement data from 115 monitors located in 14 states indicated that TCE levels ranged from 0.01 to 3.9 µg/m³, with a mean of 0.88 µg/m³. Mean TCE air concentrations (1985-1998) for rural, suburban, urban, commercial and industrial land uses were 0.42, 1.26, 1.61, 1.84 and 1.54 µg/m³, respectively (U.S. EPA, 1999a).

The mean air concentration in approximately 750 homes from 10 Canadian provinces surveyed in 1991 was 1.4 µg/m³, with a maximum value of 165 µg/m³ (Otson et al., 1992). In two homes tested, it was reported that showering with well water containing extremely high levels of TCE (40 mg/L) increased levels of TCE in bathroom air from <0.5 to 67-81 mg/m³ in less than 30 minutes (Andelman, 1985). However, it should be noted that TCE concentrations in Canadian water supplies are usually less than 1 µg/L. Therefore, the Leq/day values outlined above appear reasonable.

4.4 Food

The U.S. EPA (2001a) concluded that exposure to TCE from food was probably low and that there were insufficient food data for reliable estimates of exposure. The daily intakes of TCE in food for Canadian adults (20-70 years old) and children (5-11 years old) were estimated to range from 0.004 to 0.01 µg/kg bw per day and from 0.01 to 0.04 µg/kg bw per day, respectively (Department of National Health and Welfare, 1993). These numbers were based on TCE concentrations from U.S. food surveys from the mid- to late 1980s as well as Canadian food consumption data. In recent decades, severe restrictions have been placed on the use of TCE in food processing in North America, and the disposal of TCE is more carefully controlled in other industrial sectors. Therefore, there is no reason to suppose that these values would have increased in the interim.

* Based on the information provided, it was not possible to determine the exact TCE concentration of the seven private/domestic water supply sites (3.3%) with detectable residues; therefore, for the purposes of this calculation, it was assumed that all concentrations were >100 µg/L.