Page 6: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Tetrachloroethylene
Canadians can be exposed to tetrachloroethylene present in air, drinking water and possibly food. In addition, certain segments of the population may be exposed through the use of specific consumer products or in occupational settings. Dry cleaning and metal degreasing are the two most important occupational activities by which humans are exposed to tetrachloroethylene; inhalation is the most important route of exposure in occupational settings (IARC, 1995). Although some exposure data are available, they are considered insufficient to justify modifying the default allocation factor for drinking water of 20%.
Based on exposure data used at the time of the Priority Substances List assessment for tetrachloroethylene, the total daily intake of tetrachloroethylene was estimated to range from 1.22 to 2.67 μg/kg body weight (bw) for each of the age groups in the general population of Canada. Drinking water ingestion contributed only a minor amount to the overall exposure, estimated at 0.002 to 0.06 μg/kg bw per day (<3%). Estimated contributions of food were 0.12-0.65 μg/kg bw per day (7 to 28%). The highest contributor to exposure was air, which provided >1.22 μg/kg (>62%) of daily exposure, of which the majority (1.21 to 1.88 μg/kg per day) came from indoor air (Government of Canada, 1993).
A limited number of studies have measured tetrachloroethylene concentrations in various Canadian water bodies. As was noted in the Priority Substances List assessment report for tetrachloroethylene, concentrations of tetrachloroethylene are typically low in surface water, with exceptions occurring when industrial or other point sources released the chemical into water bodies (Government of Canada, 1993).
Recent data on concentrations of tetrachloroethylene in drinking water obtained from several provinces (see Table 1) demonstrate that concentrations are typically below the level of detection in Canadian water supplies. No provinces detected tetrachloroethylene in more than 4% of all treated water samples. Only one treated sample from all provinces contained tetrachloroethylene at a concentration of > 10 µg/L. A small proportion (10/2560) of raw water samples in Ontario contained tetrachloroethylene at concentrations above 10 µg/L, but once the water was treated and distributed, all tetrachloroethylene concentrations in the province were below 2 µg/L.
|Province (water type), years||MDL (µg/L)||No. of samples||No. (%) of samples > MDL||Average concentration (µg/L)||Maximum concentration (µg/L)|
Table 1 Footnotes
|AlbertaTable 1 footnote b, 2002-2007||NS||2353||NS||0.41||4.04|
|Saskatchewan (distributed water), 2002-2005||NS||4||NS||1||1|
|Ontario (raw water), 2002-2007||0.05||2560||151 (5.9%)||2.6Table 1 footnote c||23.1|
|Ontario (treated water), 2002-2007||0.05||2100||51 (2.4%)||0.33Table 1 footnote c||1.95|
|Ontario (distributed water), 2002-2007||0.05||2104||77 (3.7%)||0.28Table 1 footnote c||1.9|
|Quebec (distributed water), 2001-2005||0.03-1||2473||31 (1.3%)||0.55Table 1 footnote c||3.4|
|New Brunswick (municipal sources)Table 1 footnote b, 1994-2007||NS||2532||9 (0.4%)||1.2Table 1 footnote c||7|
|New Brunswick (municipal distribution)Table 1 footnote b, 1994-2007||NS||3294||12 (0.4%)||6.1Table 1 footnote c||54|
|New Brunswick (Crown sources)Table 1 footnote b, 1994-2007||NS||4304||4 (0.09%)||1.02Table 1 footnote c||2|
|New Brunswick (Crown distribution)Table 1 footnote b, 1994-2007||NS||359||0 (0%)||ND||ND|
Tetrachloroethylene was used as a solvent in the application of vinyl coating to asbestos-cement pipes during their manufacture in the 1960s and 1970s. This type of lining material was discontinued in the 1980s after the leaching of tetrachloroethylene into the drinking water was discovered (Larson et al., 1983).
Limited data are available on the level of tetrachloroethylene in food products in Canada, but food is not considered to be a major exposure pathway (Government of Canada, 1993). Food surveys in the United States have estimated the average concentrations of tetrachloroethylene in dairy, meat, cereal, fruit, vegetable, fats and oil, and sugar composite food groups to be 6.6, 12.3, 14.7, 0.8, 0.4, 12.9 and 2.9 ng/g, respectively (Heikes, 1987; Daft, 1988). Based on these surveys, the average daily intake of tetrachloroethylene through food has been estimated to be 8.4 µg.
Proximity of supermarkets to dry cleaning facilities can affect the concentration of tetrachloroethylene in foods. This has been demonstrated for butter and margarine from stores near dry cleaning facilities, which had higher tetrachloroethylene concentrations when compared with samples collected from stores with no nearby dry cleaning facilities (Entz and Diachenko, 1988; Miller and Uhler, 1988). Concentrations of tetrachloroethylene in butter from grocery stores near dry cleaning facilities exceeded 1 ppm in some samples, whereas concentrations in butter from control grocery stores were mostly ≤ 0.05 ppm (Entz and Diachenko, 1988; Miller and Uhler, 1988).
In Canada, the concentration of tetrachloroethylene in ambient (outdoor) air has been measured to range from 0.2 to 5 μg/m3 in a national survey of 22 sites in 11 Canadian cities (Dann and Wang, 1992). In indoor air, the average concentration of tetrachloroethylene was measured to be 5.1 μg/m3 in a pilot study of 757 randomly selected Canadian homes (Otson et al., 1992). In the United States, background concentrations of tetrachloroethylene lie in the low parts per trillion range in rural and remote areas and in the low parts per billion range in urban and industrial areas and areas near point sources of pollution (ATSDR, 1997). According to the European Commission (2005), the majority of measured concentrations of tetrachloroethylene in air in Europe are below 10 μg/m3, but mostly below 1 μg/m3.
Recent studies by Health Canada obtained indoor and outdoor air samples over a 24-hour period in Halifax, Nova Scotia (Health Canada, 2012), over 24-hour periods on 5 consecutive days (for 2 different years) in Windsor, Ontario (Health Canada, 2010b), and using both sampling schemes in Regina, Saskatchewan (Health Canada, 2010a). Geometric mean indoor air concentrations of tetrachloroethylene in the summer were 0.853 and 0.696 µg/m3 in Windsor, 0.548 µg/m3 for 24-hour samples in Regina and 0.257 µg/m3 in Halifax; the concentrations in winter were 0.431 and 0.321 µg/m3, 0.0426 µg/m3 and 0.269 µg/m3, respectively. Geometric mean outdoor air concentrations in the summer were 0.231 and 0.137 µg/m3 in Windsor, 0.051 µg/m3 for 24-hour samples in Regina and 0.062 µg/m3 in Halifax; the cocentrations were 0.158 and 0.119 µg/m3, 0.069 µg/m3 and 0.053 µg/m3, respectively, in winter. Personal air sampling was performed in the summer and winter of 2005 in Windsor, identifying exposure levels that were slightly higher than the indoor air concentrations (0.995 µg/m3 in summer and 0.584 µg/m3 in winter). The Regina study also investigated potential differences between smokers and non-smokers and found similar results for the two groups.
Certain activities result in an increase in personal exposure to tetrachloroethylene far above the outdoor concentrations. In a study of exposures to various volatile organic compounds (VOCs) during regular daily activities, seven volunteers (four males, three females) from four households had a mean personal air tetrachloroethylene exposure level of 8.5 μg/m3 and a mean outdoor air tetrachloroethylene exposure level of 1.2 μg/m3. An increase in tetrachloroethylene exposure was observed in one subject who visited a dry cleaner for 10 minutes and brought laundered clothes home; this subject's wife also had increased exposure (both with a 12-hour time-weighted average exposure level of 50 μg/m3). Another volunteer who used an engine carburetor cleaner for 2 hours also had elevated exposures (a 9-hour time-weighted average exposure level of 220 μg/m3) (Wallace et al., 1989).
Indoor air concentrations can become elevated in residences co-located with dry cleaning facilities using tetrachloroethylene, as demonstrated by air measurements obtained in two New York City apartment buildings with dry cleaning carried out on the ground floor. Concentrations measured in indoor air ranged from 50 to 6100 μg/m3, with mean concentrations ranging from 358 to 2408 μg/m3. After the dry cleaning operation ceased, the concentrations in the apartments declined substantially, but still ranged from 10 to 800 μg/m3 after 1 month (Schreiber et al., 2002).
Vapour intrusion is a process by which tetrachloroethylene and other VOCs from subsurface sources (e.g., soil or groundwater) move through dirt floors or crawlspaces, as well as through cracks or openings in building slabs or foundations, to be introduced inside buildings (U.S. EPA, 2012d). This process is another potential source of tetrachloroethylene in indoor air, particularly for buildings located on sites with high contamination of tetrachloroethylene in the soil or groundwater (McDonald and Wertz, 2007; U.S. EPA, 2012c).
A review of published data on personal air monitoring for tetrachloroethylene was performed to examine levels of exposure of U.S. workers to the chemical from different industries (dry cleaning, metal degreasing and other industries). The highest personal exposures came from the dry cleaning industry, where the mean tetrachloroethylene concentration was 59 parts per million (ppm) (range 0-4636 ppm, n = 1395), as well as in metal and plastics degreasing, where the mean tetrachloroethylene concentration has been measured to be 95 ppm (range 0-1800 ppm, n = 206). Lower concentrations were measured in other industries; for example, the measured mean air concentration in the production of leather products was 15 ppm (no range given, n = 71), and measurements in the printing industry gave a mean air concentration of 6 ppm (range 1.9-16 ppm, n = 22) (Gold et al., 2008).
5.4 Consumer products
Limited information is available on levels of tetrachloroethylene in Canadian consumer products, and no quantitative data are available on exposure levels from use of these products. However, in general, tetrachloroethylene can be found in some consumer products, such as spot removers, suede protectors, leather and shoe polish, adhesives, automotive chemicals, printing inks and paint removers (CAREX Canada, 2010).
Limited information is available regarding the levels of tetrachloroethylene in Canadian soil.
In Ontario, the upper 98th percentile concentrations of tetrachloroethylene in rural (n = 102) and urban (n = 59) parkland soils not impacted by pollution were found to be 1.1 and 0.87 ng/g, respectively (OMEE, 1994). Average concentrations were 0.2 and 0.18 ng/g, respectively.
Soils impacted by point sources of pollution can have higher concentrations of tetrachloroethylene. At an industrial site in Vancouver, British Columbia, tetrachloroethylene was found in soil at concentrations ranging from 0.006 to > 10 mg/kg (Golder Associates, 1989).
Tetrachloroethylene was also measured in sediments of water bodies that were affected by point sources of tetrachloroethylene. Samples of river sediment from the St. Clair River, which was selected as a sampling site due to its proximity to industrial sources, contained tetrachloroethylene at concentrations ranging from 0.006 to 0.029 mg/kg (OMOE, 1987). Tetrachloroethylene concentrations of 5.9-29 μg/kg were observed in two of five urban sediment samples obtained in Sarnia, Ontario (Marsalek, 1986). No measurements of tetrachloroethylene in unpolluted sediments in Canadian bodies of water were found.
5.6 Multiroute exposure through drinking water
Owing to tetrachloroethylene's physicochemical properties, inhalation and dermal absorption during bathing and showering may serve as important routes of exposure.
To assess the overall exposure to tetrachloroethylene in drinking water, the relative contribution of each exposure route can be assessed using a multiroute exposure assessment approach (Krishnan and Carrier, 2008). Contributions developed through this approach are expressed in litre-equivalents (L-eq) per day. Both the dermal and inhalation routes of exposure for a VOC are considered significant if they contribute at least 10% of the drinking water consumption level (Krishnan and Carrier, 2008).
A human physiologically based pharmacokinetic (PBPK) model—based on Gearhart et al. (1993), and including a showering component based on Reitz et al. (1996) and Rao and Brown (1993)—was used to estimate the contributions in L-eq from dermal and inhalation exposures to tetrachloroethylene when showering and bathing, in a manner consistent with the Krishnan and Carrier (2008) approach. The Rao and Brown (1993) model was based on blood tetrachloroethylene concentrations measured in subjects who were exposed by showering and therefore accounts for exposure to tetrachloroethylene both dissolved in the water and vaporized into the air. Using the external doses generated from the human PBPK model (see Sections 8.5 and 10), litre-equivalent contributions from dermal and inhalation exposures during showering or bathing were estimated by running the human PBPK model for a 30-minute bathing scenario. By comparing the internal doses generated from the dermal and inhalation routes of exposure with the daily internal dose estimates from ingestion, the daily litre-equivalent contributions for dermal and inhalation exposures were determined to be 1.21 and 3.45 L-eq, respectively. When added to the standard Canadian drinking water consumption rate of 1.5 L/day, the total litre-equivalent daily exposure to tetrachloroethylene in drinking water was estimated to be 6.2 L-eq (rounded).
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