Page 6: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Toluene, Ethylbenzene and the Xylenes
5.0 Exposure
For the most part, Canadians are exposed to toluene, ethylbenzene and xylenes through air, predominantly via vapours from various consumer products. Exposure through drinking water and soil can also occur, but usually to a lesser extent, although it can be considerable in areas of contamination. Although some exposure data are available, they are not sufficient to modify the default proportion of 20% of the daily intake allocated to drinking water.
5.1 Water
Toluene, ethylbenzene and xylenes have been detected at low levels in some Canadian drinking water supplies. In a 1979 study of 30 water treatment facilities across Canada, average toluene levels of 2 µg/L were measured in treated drinking water, whereas ethylbenzene and m-xylene levels were below the detection limit of 1 µg/L (Otson et al., 1982). In a study in Ontario, toluene and xylenes were detected at levels below 0.5 µg/L in samples collected from drinking water supplies, including groundwater, lake water and river water, in 1975 in proximity to and apart from the Great Lakes (Smillie et al., 1978).
Monitoring of toluene, ethylbenzene and xylenes by provinces and territories show undetectable or low levels of these chemicals in most Canadian drinking water supplies. In various locations representing all of Ontario from 2007 to 2012, toluene was detected above the method detection limit (MDL) (0.5 µg/L) in 62 of 46 472 samples; the highest concentration of toluene measured was 20.0 µg/L (Ontario Ministry of the Environment, 2012). In Manitoba, toluene, ethylbenzene and o-xylene were measured between 2007 and 2012, with the highest concentrations found being 22.0, 5.5 and 30.0 µg/L, respectively (Manitoba Conservation and Water Stewardship, 2012). From 2003 to the present, toluene, ethylbenzene and xylenes were detected in only 1%, 1.5% and 1.1% of total drinking water samples from New Brunswick (over 5000 samples), respectively; the highest detectable concentrations of these chemical components in drinking water were 1.3 µg/L for toluene, 1.4 µg/L for ethylbenzene and 7.5 µg/L for xylenes (New Brunswick Department of Health, 2012). In Quebec, maximum concentrations of toluene, ethylbenzene, o-xylene and m/p-xylene in untreated water after 2002 were 2.0, 0.12, 0.13 and 0.21 µg/L, respectively (Ministère du Développement Durable, de l'Environnement et des Parcs du Québec, 2012). Data from Saskatchewan indicate contamination event levels of toluene above 1 µg/L in 44 of 321 samples of treated drinking water, with a maximum level of 3300 µg/L; maximum levels of ethylbenzene and xylenes were reported to be 550 and 2825 µg/L, respectively, from 1989 to 2012 (Saskatchewan Ministry of Environment, 2012). Over the 2002 to 2012 time period the maximum levels detected for toluene, ethylbenzene and xylenes in Saskatchewan treated drinking water were 22, 16 and 7 µg/L, respectively.
5.2 Food
There is a lack of information regarding the presence and concentrations of toluene, ethylbenzene and xylenes in food in Canada. The U.S. Food and Drug Administration total diet study reported mean levels of toluene below 0.17 part per million (ppm), ethylbenzene below 0.01 ppm and xylenes below 0.02 ppm in approximately 280 food items, including breads and cereal, dairy products, desserts, fruits and vegetables, as well as raw and prepared meats, from 1991 to 2004 (U.S. FDA, 2008). Toluene, ethylbenzene and xylenes can also be present in food as a result of water use during preparation or indirectly from components of commercial packaging.
5.3 Air
Since toluene, ethylbenzene and xylenes strongly partition to the atmosphere, exposure via air can be considerable. Mean concentrations of toluene in ambient air have been shown to range from 1.0 to 30.7 µg/m3 in various Canadian cities (Dann et al., 1989; Ontario Ministry of Environment and Energy, 2000), whereas mean concentrations of ethylbenzene were shown to range from 0.1 to 17.0 µg/m3 (Ontario Ministry of Environment and Energy, 2000; Alberta Environment, 2004). Mean concentrations of xylenes in ambient air at Canadian urban and suburban sites ranged from 0.6 to 20.4 µg/m3 (Dann et al., 1989; Ontario Ministry of Environment and Energy, 2000). Generally, concentrations of these compounds were lower in rural areas. Mean concentrations of 4.9 and 4.3 µg/m3 have been reported in rural Walpole Island, Ontario, for toluene and xylenes, respectively (Dann et al., 1989).
Important exposures to toluene, ethylbenzene and xylenes can also occur indoors. Studies of households across Canada spanning all four seasons have reported mean concentrations ranging from 2.5 to 84.3 µg/m3 and from 0.6 to 14.0 µg/m3 for toluene and ethylbenzene, respectively (Fellin and Otson, 1994; Zhu et al., 2005; Héroux et al., 2008). Mean concentrations of xylene isomers ranged from 0.8 to 8.2 µg/m3 for o-xylene and from 1.8 to 34.2 µg/m3 for m/p-xylene (Fellin and Otson, 1994; Zhu et al., 2005; Héroux et al., 2008).
In 2005–2006, as part of a personal exposure monitoring campaign funded under the Border Air Quality Strategy, Health Canada and the University of Windsor collected 24-hour personal, indoor and outdoor exposure samples for 188 polar and non-polar volatile organic compounds (VOCs) (Health Canada, 2010a). In total, 100 study participants in Windsor, Ontario, were followed over two 1-year periods. Sampling took place in 8-week "winter" and "summer" periods of 2005 and 2006, when five consecutive 24-hour VOC sampling measurements were obtained to represent indoor, outdoor and personal exposure levels (2005 only). Over the 2-year period, median concentrations of toluene in indoor air ranged from 8.3 to 23.5 µg/m3, and median concentrations in outdoor air ranged from 1.9 to 4.3 µg/m3. Median concentrations of ethylbenzene in indoor air ranged from 1.1 to 2.9 µg/m3, and median concentrations in outdoor air ranged from 0.3 to 0.6 µg/m3. Median concentrations of xylene in indoor air ranged from 1.0 to 8.6 µg/m 3, and median concentrations in outdoor air ranged from 0.3 to 1.6 µg/m3. Similar trends were reported in a recent study conducted in Regina, Saskatchewan (Health Canada, 2010b).
Data on Canadian concentrations of toluene, ethylbenzene and xylenes in indoor and ambient air are similar to those reported in the United States (ATSDR, 2000, 2007, 2010).
5.4 Soil
Data on concentrations of toluene, ethylbenzene and xylenes in soil in Canada and other countries are scarce. The Ontario Ministry of Environment and Energy reported 98th percentile concentrations of toluene, ethylbenzene and xylenes to be 0.9, 0.4 and 0.8 µg/kg in old urban parkland soils and 0.9, 0.5 and 0.9 µg/kg in rural parkland soils, respectively (OMEE, 1993). Neither of these regions was affected by local point source pollution. Due to the fate of toluene, ethylbenzene and xylenes in the environment, levels of these compounds in soil are generally low, with considerable contamination occurring only in areas near hazardous waste sites or in cases of chemical spills.
5.5 Consumer products
Due to their extensive use as solvents and their presence in fuels, toluene, ethylbenzene and xylenes are frequently found in various consumer products. These products include gasoline and diesel fuel, paints and inks, as well as various cleaners, polishes and adhesives. Storage of such products is a frequent means of exposure to toluene, ethylbenzene and xylenes. For example, vapours from stored materials or from vehicular exhaust can enter indoor environments via adjacent garages (Graham et al., 2004; Dodson et al., 2008). Cigarette smoking can also be a significant source of exposure to toluene, ethylbenzene and xylenes.
5.6 Multi-route exposure through drinking water
A human physiologically based pharmacokinetic (PBPK) model that was developed for toluene, ethylbenzene and xylenes using data from Tardif et al. (1997) was extended to include a dermal component for assessing multiple routes of exposure. The model was developed in order to extrapolate inhalation data from rats, mice and occupationally exposed workers (Korsak et al., 1994; NTP, 1999; Seeber et al., 2004, 2005) to humans exposed to low concentrations of each chemical in drinking water. The model was also used to estimate litre-equivalent (L-eq) contributions from dermal and inhalation exposures when showering and bathing. Using the external doses generated from the human PBPK model (see Section 8.5.4), 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 internal dose from ingestion in accordance with total body weight, the litre-equivalent contributions for dermal and inhalation exposures were estimated to be 0.2 L-eq and 0.43 L-eq for toluene, 0.21 L-eq and 0.44 L-eq for ethylbenzene, and 0.21 L-eq and 0.43 L-eq for xylenes, respectively. When added to the standard Canadian drinking water consumption rate of 1.5 L/day, the total litre-equivalent daily exposures to toluene, ethylbenzene and xylenes in drinking water were estimated to be 2.13, 2.15 and 2.14 L-eq, respectively. These litre-equivalent daily exposures were used in both the cancer and non-cancer risk assessments in Section 10.
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