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

5.0 Exposure

This section summarizes the results of federal programs that monitor the levels of radionuclides in water supplies across Canada. It illustrates which radionuclides occur most frequently in Canadian waters, at what concentrations, and in what geological or geographical settings. The results of provincial/territorial monitoring surveys are presented in Appendix C.

From 1973 to 1983, the Radiation Protection Bureau of Health Canada monitored the levels of the natural radionuclides 226Ra, 210Pb, and total uranium in the drinking water supplies of 17 communities across Canada (Health Canada, 2000a). Most of these communities utilized surface water supplies, and the radionuclide concentrations were consistently low or non-detectable. The concentrations measured were as follows: uranium, < 0.1-1 µg/L; 226Ra, < 0.005-0.02 Bq/L; and 210Pb, < 0.005-0.02 Bq/L.

After 1983, the program was reduced to just three municipalities: Elliot Lake and Port Hope (because of uranium mining and processing activities possibly impacting surface water supplies) and Regina (because of elevated uranium levels in the groundwater supply). During the later period, only 226Ra and total uranium were monitored; the levels of 210Pb had been shown to be consistently low or non-detectable in surface waters. The results for a 14-year period, from 1983 to 1996, are summarized in Table C-1 in Appendix C. Elliot Lake showed a slight elevation in 226Ra at the beginning of this period, although there appears to have been a gradual decline in both 226Ra and total uranium levels towards the end of the period. It is likely that detectable levels of 226Ra and total uranium in the Elliot Lake results were due to higher levels of natural radionuclides in a uranium-rich region rather than to uranium mining operations. Radium levels in Port Hope remained non-detectable throughout this period, and uranium concentrations were within the normal range for surface water supplies.

Drinking water for the city of Regina consistently showed uranium levels that are elevated above national averages, but still well below 20 µg/L. Radium-226 levels remained below the detection limit of 0.005 Bq/L during the period 1983-1996. Historically, Regina derived its drinking water from both surface water and groundwater sources and adjusted the blend according to water quality and availability. Consequently, the uranium concentrations varied from year to year and from season to season.

The National Water Research Institute (Canada Centre for Inland Waters) of Environment Canada monitored radioactivity in Canadian surface waters from 1973 to the mid-1980s. Much of this work was focused on open waters of the Great Lakes (Durham and Joshi, 1981). A special project was carried out from 1981 to 1984 to characterize the levels of 226Ra, 137Cs, 125Sb, tritium, and uranium at 13 sites scattered across Canada (Baweja et al., 1987). Concentrations measured were as follows: 226Ra, 0.001-0.013 Bq/L; 137Cs, 0.0007-0.006 Bq/L; 125Sb, 0.001-0.016 Bq/L; tritium, 5-12 Bq/L; and uranium, 0.16-4.7 µg/L.

From 1962 to 1994, Health Canada's Radiation Protection Bureau monitored 90Sr and 137Cs routinely in the drinking water supplies of communities located near nuclear reactor facilities (Health Canada, 2000a). Table C-2 in Appendix C compares the open lake results for 90Sr and 137Cs with results from locations near the Pickering and Bruce nuclear generating stations. The results near the nuclear generating stations are quite similar to the open lake values, confirming the conclusion that all 90Sr and 137Cs levels are due to global fallout rather than to emissions from nuclear reactors.

The results also show that concentrations of these radionuclides have varied with time and from one lake to another. Radionuclides are gradually removed from Great Lakes waters by radioactive decay, sedimentation, and flushing. Tracy and Prantl (1983) analysed the earlier data from Lakes Superior and Huron and found very slow half-times for removal of 90Sr from water (20 years for Lake Superior; 10 years for Lake Huron). The 137Cs concentrations showed two removal components: one fast, with the bulk of the activity being removed in much less than 1 year, and the other slower and more persistent, with a half-time of several years. They attributed this slow component to re-entry from lake sediments.

Monitoring of drinking water intakes downstream from the Gentilly nuclear reactor in Quebec has not shown any evidence of contamination by fission or activation products. Liquid releases from the Point Lepreau nuclear generating station in New Brunswick enter directly into the Bay of Fundy and thus do not impact drinking water supplies.

Average tritium concentrations in surface waters across Canada are on the order of 5-12 Bq/L (Baweja et al., 1987). Great Lakes open water values ranged from 7 to 10 Bq/L during 1982-1984. Chant et al. (1993) reported average tritium concentrations in Lake Ontario of 9-11 Bq/L. They concluded that only about 10% of this amount could be due to reactor releases from Pickering.

Occasionally, upsets at nuclear facilities have given rise to brief increases in tritium levels at nearby drinking water intakes. These increases have always been of short duration, not lasting more than a few days. In June 1991, Health Canada monitored the levels of tritium in the Ottawa River following a spill from Chalk River Nuclear Laboratories. The highest concentration reached in drinking water was about 400 Bq/L at Petawawa. At Ottawa (200 km downstream), the levels had been diluted to about 150 Bq/L. Minute traces of tritium from the release were detected at Montreal, past the point of confluence of the Ottawa and St. Lawrence rivers. In September 1983, a release of 222 TBq of tritium from the Douglas Point reactor on the Bruce Peninsula, Ontario, provided an opportunity to model the dispersal of tritium in Lake Huron (Veska and Tracy, 1986). A prevailing counter-clockwise circulation pattern in the lake carried the tritium plume northeastward to Port Elgin, where drinking water levels reached 1600 Bq/L during a 2-day period.

The Newfoundland and Labrador Department of the Environment (Guzwell, 2002) initiated a program of screening public water supplies for natural radionuclides by testing for uranium. Of the 128 public groundwater supplies tested, only one contained uranium at a concentration above 20 µg/L (79 µg/L). Retesting this one supply for 210Pb and 226Ra showed these parameters to be well below the current Canadian drinking water guidelines. One private well, which has since been abandoned, had a uranium concentration of 160 µg/L. Testing was also carried out at public schools utilizing groundwater sources. Two water supplies out of 68 tested had uranium levels above 20 µg/L (51 and 78 µg/L). In both cases, the water fountains were turned off, and other sources of drinking water were provided.

In Nova Scotia, extensive uranium mineralizations have led to elevated concentrations of radionuclides at a number of locations. In a 2002 survey (Drage et al., 2005), 52 public school water wells were tested for total uranium and 14 naturally occurring radionuclides, most of which are daughter products of the uranium and thorium decay series. The results are summarized in Table 1.

Table 1. Radionuclide results for 52 school water wells in Nova Scotia
Radionuclide Maximum level Number of guideline exceedances
7Be < 5 Bq/L -
210Bi 0.44 Bq/L -
210Pb 0.24Table 1 Footnote 1 Bq/L 1 of 52 (2%)Table 1 Footnote 1
210Po 0.12 Bq/L -
224Ra < 0.01 Bq/L -
226Ra 0.04 Bq/L -
228Ra 0.14 Bq/L -
228Th < 0.01 Bq/L -
230Th 0.01 Bq/L -
232Th < 0.01 Bq/L -
234Th < 4 Bq/L -
234U 1 Bq/L -
235U 0.05 Bq/L -
238U 1 Bq/L -
Total uranium 0.081 mg/L 2 of 52 (4%)

Table 1 Footnotes

Table 1 Footnote 1

The original sampling results from this survey showed that 12 water supplies exceeded the 210Pb guideline; however, it was subsequently determined that radon decay in the sample bottles had affected the sample results. Follow-up sampling, which corrected for radon decay effects, showed that only one of these water supplies exceeded the 210Pb guideline.

Return to Table 1 footnote 1 referrer

A follow-up survey (Drage et al., 2005) tested for total uranium, 210Pb, and 226Ra at all public schools in Nova Scotia with drilled wells (178 wells). The results in Table 2 show that the maximum 210Pb level was 0.24 Bq/L, and the maximum total uranium concentration was 0.12 mg/L.

Table 2. Radionuclide results for 178 school water wells in Nova Scotia
Radionuclide Maximum level Number of guideline exceedances
210Pb 0.24 Bq/L 1 of 178 (< 1%)
226Ra 0.08 Bq/L -
Total uranium 0.12 mg/L 3 of 178 (2%)

New Brunswick has geological formations similar to those of Nova Scotia; thus, there is the potential for entry of natural radionuclides into groundwater. In the summer of 1983, Health Canada carried out a survey of natural radionuclides from 53 community wells across New Brunswick. The results are summarized in Table 3. These levels are typical of background levels across Canada; however, in a separate survey, wells from at least one community, Harvey Station, had uranium concentrations of 0.01-0.4 mg/L.

Table 3. 1983 survey of New Brunswick wells
Radionuclide Mean level Range
Uranium 0.013 mg/L 0.0001-0.0039 mg/L
226Ra 0.0032 Bq/L 0.0001-0.012 Bq/L
222Rn 13.4 Bq/L 0.2-39 Bq/L

In Ontario, the average concentration of tritium in over 3000 drinking water samples taken between 2000 and 2006 was 5-10 Bq/L. Single values of 120 Bq/L and 24 Bq/L, respectively, were observed in raw water at Southampton and Port Elgin, near the outflow of the Bruce Nuclear Power Development. One value of 18 Bq/L was observed at the R.C. Harris water treatment plant in Toronto. Earlier, from 1989 to 1992, a subset of about 530 Ministry of Labour samples was collected from surface waters known to have been impacted by uranium mining and milling operations (MOEE, 1993). The ranges of measured 224Ra and uranium concentrations are shown in Table 4. The highest 224Ra concentration was 12 Bq/L, and the highest uranium concentration was 2.9 mg/L. Note that these water bodies were not being used as sources of drinking water.

Table 4. Concentrations of 224Ra and uranium in Ontario surface waters near uranium mining and milling operations from 1989 to 1992
Range of 224Ra concentrations (Bq/L) Number of samples within the range Range of uranium concentrations (mg/L) Number of samples within the range
0-0.05 385 0-0.02 413
> 0.05-0.1 88 > 0.02-0.1 89
> 0.1-0.5 51 > 0.1-1 27
> 0.5 4 > 1 4
Total number of samples 528 Total number of samples 533

More recent data (2000-2006) from the Ontario Ministry of the Environment's Drinking Water Surveillance Program indicated that the highest level of gross alpha activity in drinking water was 0.95 Bq/L, the highest level of gross beta activity was 0.38 Bq/L, and the highest level of tritium was 16 Bq/L. The corresponding levels in the raw water are similar.

In Saskatchewan, approximately 16 communities have uranium levels in drinking water that relatively consistently exceed 0.020 mg/L. The maximum concentration of uranium detected in a Saskatchewan municipal water supply is 0.039 mg/L; however, water from this system is reportedly not consumed.

5.1 Radon

Radon is the most important source of naturally occurring radiation exposure for humans. For the world population, radon exposure represents 43% of the total exposure to natural background radiation, followed by Earth gamma radiation at 15%, cosmic radiation at 13% and natural radiation from food and water at 8% (WHO, 2008). Ninety-five percent of exposure to radon is from indoor air, with about 1% coming from drinking water (WHO, 2004).

There are few data on radon concentrations in Canadian drinking water supplies. Water drawn from surface water supplies does not generally contain appreciable levels of radon, which are expected to be on the order of 0.01 Bq/L. One survey of Canadian groundwater sources containing elevated levels of radon found radon concentrations in the range 1700-13 700 Bq/L in Halifax County, Nova Scotia. A second survey detected radon at concentrations as high as 3000 Bq/L in well water in Harvey, New Brunswick, with 80% of the wells containing radon concentrations below 740 Bq/L. In a more recent study, as part of a province-wide radionuclide testing program, levels of radon were measured in the drinking water from 16 schools in Nova Scotia; radon levels reportedly ranged from 120 to 1400 Bq/L, with an average of approximately 600 Bq/L (Drage et al., 2005). Levels of radon this high in drinking water can lead to significant levels of 210Pb in only a few days (Drage et al., 2005).

The major concern for radon gas as a hazard is its occurrence in the air inside buildings and underground work areas. In air, the principal effect is to the lung, because of the inhalation and accumulation within the respiratory system of the short-lived decay products attached to inert dust particles normally present in the atmosphere. Although radon may be ingested through drinking water, radon contained in water is, to some extent, transferred to air, and therefore the total radiation exposure can result from both ingestion and inhalation.

The relationship between the concentration of radon in the water supply and the concentration of radon in indoor air depends on several factors, including the rate and type of usage of the water (e.g., drinking water, showers, laundry), the loss or transfer of radon from the water to the air, and the characteristic ventilation of the house. The rate of release of radon from water depends on such factors as agitation, surface area, and temperature. Numerous authors (Cothern, 1987; UNSCEAR, 1988; Life Systems Inc., 1991; U.S. EPA, 1991) have reported a water-to-air transfer factor of 10-4 for a typical residential dwelling, which would mean that a radon concentration of 1000 Bq/L in drinking water would on average increase the indoor air radon concentration by 100 Bq/m3, with the highest concentration being expected in the rooms where radon is released (UNSCEAR, 1988). Nazaroff et al. (1987) estimated that, based on measurements in U.S. homes and water supplies, public supplies derived from groundwater serving 1000 or more persons contribute about 2% to the mean indoor radon concentration for houses using these sources. The average doses from radon in drinking water have been calculated as being as low as 0.025 mSv/year via inhalation and 0.002 mSv/year via ingestion, compared with the background inhalation dose of 1.1 mSv/year from air (UNSCEAR, 2000).

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