A DISCUSSION ON ISSUES WITH RADON IN DRINKING WATER

A DISCUSSION ON ISSUES WITH RADON IN DRINKING WATER Abstract The majority of the world’s population relies on surface water or large public supply systems of groundwater, where radon is low and a guidance value for radon in drinking water is not necessary. However, the International Commission on Radiological Protection (ICRP) recently issued a dose coefficient for radon ingestion, raising questions among some radiation protection authorities about whether radon guidance values should be calculated for drinking water and how this might be done. Unlike many other radionuclides considered in drinking water management, radon has special characteristics and therefore requires special considerations. This note discusses some of these considerations, and also provides a brief review of radon concentrations measured in well-water supplies, especially private well-water systems, and cold tap water consumption rates reported in different countries. INTRODUCTION Radon (222Rn) is a chemically inert gas formed through the radioactive decay of 226Ra. Both are members of the 238U decay series. Uranium and radium occur naturally in soil and rocks, and provide a continuous source of radon. Radon can escape from the Earth’s crust and is present in the air everywhere in varying concentrations. Uranium, radium and radon can also dissolve in water and, therefore, may enter groundwater supplies that pass through radium-bearing rocks and soils. While water drawn from surface water supplies does not generally contain appreciable levels of radon, high radon concentrations are often observed in groundwater sources(1). Almost all radon management policies focus on radon in the air because radon inhalation is recognised as the largest contributor to background radiation dose. Health risks posed by ingesting radon in drinking water are thought to be insignificant compared to the risks posed by the transfer of radon into air through outgassing and its subsequent inhalation(2–4). An evaluation of international research data(2) has concluded that, on average, 90% of the dose attributable to radon in drinking water comes from inhalation rather than ingestion. Because of this, many drinking water guidelines do not include a guidance value for radon, or base their recommendations on risks of contributing to the indoor air concentration and resulting inhalation hazard(3, 4). For example, in the recent publication on the management of radioactivity in drinking water(5), WHO elected not to provide guidance level for radon in drinking water because it is considered more appropriate to measure and manage radon concentrations in indoor air. The International Commission on Radiological Protection (ICRP) recently issued a dose coefficient for radon ingestion(6), raising questions among some radiation protection authorities about whether radon guidance values for drinking water should be calculated and how this might be done. Unlike many other radionuclides considered in drinking water management, radon has special characteristics and therefore requires special considerations. This paper discusses some of these considerations, and also provides a brief review of radon concentrations measured in well-water supplies, especially private well-water systems, as reported in the published literature. RADON LEVELS IN GROUNDWATER SOURCES The most common conclusions of the studies on radon in groundwater and public water supplies in the USA suggest that the highest radon concentrations generally occur in portions of Appalachian Mountains, Rocky Mountains, and Basin and Range where uranium-bearing metamorphosed rocks, volcanics, and granite intrusive rocks are predominantly found(1). Private well sources and small public water supplies tend to have more radon than large public water supplies because they are often drawn from aquifers with low capacity. When these types of aquifers are uranium-bearing granite, metamorphic rocks, or fault zones, the radon concentration in the water tends to be high. Large public water supplies tend to use high-capacity sand and gravel aquifers, which are generally comprised of low-uranium rocks and sediments and tend to be lower in radon. The radon concentrations in the large public water supply systems of Canadian cities are very low; for example, less than 10 Bq/l in Ottawa, and below detection limits in Vancouver(7). A brief summary of radon concentrations in drinking water from well water or ground water sources is given in Table 1. The measured results show clearly that groundwater that passes through radium-bearing rocks and soils can have high radon concentrations; however, the variation is large. In Canada, an average radon concentration of 600 Bq/l was observed in well water of 16 schools in Nova Scotia while a median radon concentration of 9 Bq/l was found in 198 wells in the province of Quebec. In Finland, the average radon concentration was 50 Bq/l in dug wells, but about 10 times higher in drilled wells. A survey of 1604 groundwater samples from Norwegian crystalline bedrock aquifers showed that 14% wells had radon concentration above 500 Bq/l and a maximum radon concentration of 31 900 Bq/l was observed. Table 1. Radon concentrations in groundwater or well water measured in various locations (arithmetic mean (AM), median, range and other reported characteristics). Location # Samples Radon concentration Reference Curitiba, Brazil 31 AM = 44 Bq/l; 1.6–251 Bq/l Correa et al.(8) Rio de Janeiro, Brazil 88 AM < 3 Bq/l; < 3–75 Bq/l Almeida et al.(9) Nova Scotia, Canada 16 AM = 600 Bq/l; 120–1400 Bq/l Drage et al.(10, 11) Quebec, Canada 198 Median = 9 Bq/l; 0.2–310 Bq/l; 90% < 100 Bq/l Pinti et al.(12) Fujian, China 552 AM = 229 Bq/l; 0.7–3735 Bq/l Zhuo et al.(13) Czech 300 AM = 87 Bq/l; 5–1600 Bq/l Otahal et al.(14) Finland 184 (dug wells) AM = 50 Bq/l; max = 710 Bq/l Vesterbacka et al.(15) 288 (drilled wells) AM = 460 Bq/l; max = 8600 Bq/l; 10% > 1000 Bq/l Busan, Korea 439 AM = 36 Bq/l; 0–300 Bq/l Cho et al.(16) Norway 1604 (bedrock) 14% > 500 Bq/l; max = 31 900 Bq/l Banks et al.(17) 72 Median = 22 Bq/l; <10–410 Bq/l Banks et al.(18) Southern Greater Poland 89 AM = 2.7 Bq/l; 0.4–10.5 Bq/l Bem et al.(19) Karkonosze, Poland 199 AM = 212 Bq/l; 0.3–1392 Bq/l Przylibski and Gorecka(20) Spain 350 AM = 111 Bq/l; 35% > 100 Bq/l Lopez and Sanchez(21) Sweden 328 (drilled wells) AM = 573 Bq/l; 5–8105 Bq/l; 80% > 100 Bq/l Salih et al.(22) Location # Samples Radon concentration Reference Curitiba, Brazil 31 AM = 44 Bq/l; 1.6–251 Bq/l Correa et al.(8) Rio de Janeiro, Brazil 88 AM < 3 Bq/l; < 3–75 Bq/l Almeida et al.(9) Nova Scotia, Canada 16 AM = 600 Bq/l; 120–1400 Bq/l Drage et al.(10, 11) Quebec, Canada 198 Median = 9 Bq/l; 0.2–310 Bq/l; 90% < 100 Bq/l Pinti et al.(12) Fujian, China 552 AM = 229 Bq/l; 0.7–3735 Bq/l Zhuo et al.(13) Czech 300 AM = 87 Bq/l; 5–1600 Bq/l Otahal et al.(14) Finland 184 (dug wells) AM = 50 Bq/l; max = 710 Bq/l Vesterbacka et al.(15) 288 (drilled wells) AM = 460 Bq/l; max = 8600 Bq/l; 10% > 1000 Bq/l Busan, Korea 439 AM = 36 Bq/l; 0–300 Bq/l Cho et al.(16) Norway 1604 (bedrock) 14% > 500 Bq/l; max = 31 900 Bq/l Banks et al.(17) 72 Median = 22 Bq/l; <10–410 Bq/l Banks et al.(18) Southern Greater Poland 89 AM = 2.7 Bq/l; 0.4–10.5 Bq/l Bem et al.(19) Karkonosze, Poland 199 AM = 212 Bq/l; 0.3–1392 Bq/l Przylibski and Gorecka(20) Spain 350 AM = 111 Bq/l; 35% > 100 Bq/l Lopez and Sanchez(21) Sweden 328 (drilled wells) AM = 573 Bq/l; 5–8105 Bq/l; 80% > 100 Bq/l Salih et al.(22) Table 1. Radon concentrations in groundwater or well water measured in various locations (arithmetic mean (AM), median, range and other reported characteristics). Location # Samples Radon concentration Reference Curitiba, Brazil 31 AM = 44 Bq/l; 1.6–251 Bq/l Correa et al.(8) Rio de Janeiro, Brazil 88 AM < 3 Bq/l; < 3–75 Bq/l Almeida et al.(9) Nova Scotia, Canada 16 AM = 600 Bq/l; 120–1400 Bq/l Drage et al.(10, 11) Quebec, Canada 198 Median = 9 Bq/l; 0.2–310 Bq/l; 90% < 100 Bq/l Pinti et al.(12) Fujian, China 552 AM = 229 Bq/l; 0.7–3735 Bq/l Zhuo et al.(13) Czech 300 AM = 87 Bq/l; 5–1600 Bq/l Otahal et al.(14) Finland 184 (dug wells) AM = 50 Bq/l; max = 710 Bq/l Vesterbacka et al.(15) 288 (drilled wells) AM = 460 Bq/l; max = 8600 Bq/l; 10% > 1000 Bq/l Busan, Korea 439 AM = 36 Bq/l; 0–300 Bq/l Cho et al.(16) Norway 1604 (bedrock) 14% > 500 Bq/l; max = 31 900 Bq/l Banks et al.(17) 72 Median = 22 Bq/l; <10–410 Bq/l Banks et al.(18) Southern Greater Poland 89 AM = 2.7 Bq/l; 0.4–10.5 Bq/l Bem et al.(19) Karkonosze, Poland 199 AM = 212 Bq/l; 0.3–1392 Bq/l Przylibski and Gorecka(20) Spain 350 AM = 111 Bq/l; 35% > 100 Bq/l Lopez and Sanchez(21) Sweden 328 (drilled wells) AM = 573 Bq/l; 5–8105 Bq/l; 80% > 100 Bq/l Salih et al.(22) Location # Samples Radon concentration Reference Curitiba, Brazil 31 AM = 44 Bq/l; 1.6–251 Bq/l Correa et al.(8) Rio de Janeiro, Brazil 88 AM < 3 Bq/l; < 3–75 Bq/l Almeida et al.(9) Nova Scotia, Canada 16 AM = 600 Bq/l; 120–1400 Bq/l Drage et al.(10, 11) Quebec, Canada 198 Median = 9 Bq/l; 0.2–310 Bq/l; 90% < 100 Bq/l Pinti et al.(12) Fujian, China 552 AM = 229 Bq/l; 0.7–3735 Bq/l Zhuo et al.(13) Czech 300 AM = 87 Bq/l; 5–1600 Bq/l Otahal et al.(14) Finland 184 (dug wells) AM = 50 Bq/l; max = 710 Bq/l Vesterbacka et al.(15) 288 (drilled wells) AM = 460 Bq/l; max = 8600 Bq/l; 10% > 1000 Bq/l Busan, Korea 439 AM = 36 Bq/l; 0–300 Bq/l Cho et al.(16) Norway 1604 (bedrock) 14% > 500 Bq/l; max = 31 900 Bq/l Banks et al.(17) 72 Median = 22 Bq/l; <10–410 Bq/l Banks et al.(18) Southern Greater Poland 89 AM = 2.7 Bq/l; 0.4–10.5 Bq/l Bem et al.(19) Karkonosze, Poland 199 AM = 212 Bq/l; 0.3–1392 Bq/l Przylibski and Gorecka(20) Spain 350 AM = 111 Bq/l; 35% > 100 Bq/l Lopez and Sanchez(21) Sweden 328 (drilled wells) AM = 573 Bq/l; 5–8105 Bq/l; 80% > 100 Bq/l Salih et al.(22) CHARACTERISTICS OF RADON IN WATER Radon is fairly soluble in water, with its solubility decreasing rapidly with increasing temperature. The coefficient of radon solubility as a function of water temperature is shown in Figure 1. One can see clearly that radon will escape to the air during normal household activities, such as cooking. Figure 1. View largeDownload slide Coefficients of radon solubility in water as a function of water temperature (data taken from UNSCEAR 1982 Report(23)). Figure 1. View largeDownload slide Coefficients of radon solubility in water as a function of water temperature (data taken from UNSCEAR 1982 Report(23)). Radon is also extremely volatile and readily released from water into air. It can escape from water even when running water from the tap to a container before drinking. In situations where water is both heated and agitated, such as boiling water for tea, it is assumed that most of the radon ends up in the air. The US Committee on Risk Assessment of Exposure to Radon in Drinking Water assessed the transfer of radon from water to indoor air(1) from a range of household activities, including showering and dishwashing. It showed that there is reasonable agreement between the average value of transfer coefficient estimated by the models and the value calculated from measured data, which led to a recommendation of 1.0 × 10−4 as the best central estimate of the transfer coefficient. Based on this transfer coefficient and the Canadian action level for radon in indoor air (200 Bq/m3)(24), the Canadian Drinking Water Guidelines(4) recommend that actions be taken to manage radon in water if the concentration exceeds 2000 Bq/l. The fact that radon readily outgases from water makes water treatment relatively easy. Public water supply systems can easily reduce radon in water by various aeration methods, with removal efficiency from at least 70% to more than 99%(1). COLD WATER CONSUMPTION Due to the characteristics of radon in water described above, the ingestion dose from radon will depend on how the water is consumed, and will be almost entirely from cold water directly ingested from the tap (rather than water that is heated, boiled or otherwise treated). Based on data collected by the US Department of Agriculture 1977-1978 Nationwide Food Consumption Survey, the estimated mean value of daily water intake was 1.2 l/day for all uses of tap water which consists of both direct use (i.e. direct ingestion) and indirect use (i.e. making coffee, tea, etc)(1). The US EPA has estimated that slightly more than half of the tap water used is directly ingested, or about 0.6 l/day for direct use(25). A pooled analysis of seven cross-sectional studies from Newfoundland and Labrador, Waterloo and Hamilton Regions, Ontario and Vancouver, East Kootenay and Northern Interior Regions, British Columbia (2001–2007) was performed to investigate the drinking water consumption patterns of Canadians and to identify factors associated with the volume of tap water consumed(26). Tap water was defined as water directly from the tap with no subsequent treatment. The mean volume of tap water consumed among 6325 tap water users was 1.2 ± 0.8 l/day. A brief summary of surveys on daily consumption of cold tap water in seven countries is given in Table 2. The average cold water consumption rate varied from 0.18 to 1.2 l/day with an overall average of 0.7 l/day. In all seven countries, the mean daily volume of cold water consumed was significantly lower than the default assumption of 2 l/day that is often used when calculating guidance levels. However, it is clear that daily consumption of water can vary with the amount of physical activity performed by an individual as well as with fluctuations in temperature and humidity. For example, people may drink more in summer than in winter, and people who live in warmer climates might have higher intakes of water. Table 2. Daily consumption of cold tap water (litres). Country Daily consumption of cold tap water (l) Note Reference Canada 1.2 ± 0.8 n = 6325; highly variable 0.03–9.0 l/day; highest for ages 18-29 y, lower in older ages; females (>29 y) drank more than males Roche et al.(26) Finland 0.5 0.5 l/day for radon, 2.2 l/day for all other radionuclides when calculating ingestion dose Vesterbacka et al.(15) France 0.8 ± 0.6 n = 1918; women consumed more cold tap water than men. Gazan et al.(27) Netherlands 0.18 n = 6250 Mons et al.(28) Norway 0.58 Hanssen et al.(29) Sweden 0.86 ± 0.48 n = 11189; women consumed more cold tap water than men; cold tap water intake was highest in oldest age group (>70 yrs) Westrell et al.(30) USA 0.92 n = 16,566; vary widely 0–2.3 l/day; women drink more plain tap water than men for all age groups Sebastian et al.(31) Country Daily consumption of cold tap water (l) Note Reference Canada 1.2 ± 0.8 n = 6325; highly variable 0.03–9.0 l/day; highest for ages 18-29 y, lower in older ages; females (>29 y) drank more than males Roche et al.(26) Finland 0.5 0.5 l/day for radon, 2.2 l/day for all other radionuclides when calculating ingestion dose Vesterbacka et al.(15) France 0.8 ± 0.6 n = 1918; women consumed more cold tap water than men. Gazan et al.(27) Netherlands 0.18 n = 6250 Mons et al.(28) Norway 0.58 Hanssen et al.(29) Sweden 0.86 ± 0.48 n = 11189; women consumed more cold tap water than men; cold tap water intake was highest in oldest age group (>70 yrs) Westrell et al.(30) USA 0.92 n = 16,566; vary widely 0–2.3 l/day; women drink more plain tap water than men for all age groups Sebastian et al.(31) Table 2. Daily consumption of cold tap water (litres). Country Daily consumption of cold tap water (l) Note Reference Canada 1.2 ± 0.8 n = 6325; highly variable 0.03–9.0 l/day; highest for ages 18-29 y, lower in older ages; females (>29 y) drank more than males Roche et al.(26) Finland 0.5 0.5 l/day for radon, 2.2 l/day for all other radionuclides when calculating ingestion dose Vesterbacka et al.(15) France 0.8 ± 0.6 n = 1918; women consumed more cold tap water than men. Gazan et al.(27) Netherlands 0.18 n = 6250 Mons et al.(28) Norway 0.58 Hanssen et al.(29) Sweden 0.86 ± 0.48 n = 11189; women consumed more cold tap water than men; cold tap water intake was highest in oldest age group (>70 yrs) Westrell et al.(30) USA 0.92 n = 16,566; vary widely 0–2.3 l/day; women drink more plain tap water than men for all age groups Sebastian et al.(31) Country Daily consumption of cold tap water (l) Note Reference Canada 1.2 ± 0.8 n = 6325; highly variable 0.03–9.0 l/day; highest for ages 18-29 y, lower in older ages; females (>29 y) drank more than males Roche et al.(26) Finland 0.5 0.5 l/day for radon, 2.2 l/day for all other radionuclides when calculating ingestion dose Vesterbacka et al.(15) France 0.8 ± 0.6 n = 1918; women consumed more cold tap water than men. Gazan et al.(27) Netherlands 0.18 n = 6250 Mons et al.(28) Norway 0.58 Hanssen et al.(29) Sweden 0.86 ± 0.48 n = 11189; women consumed more cold tap water than men; cold tap water intake was highest in oldest age group (>70 yrs) Westrell et al.(30) USA 0.92 n = 16,566; vary widely 0–2.3 l/day; women drink more plain tap water than men for all age groups Sebastian et al.(31) RADON INGESTION DOSE In the recent ICRP Publication 137(6), a new biokinetic model for systemic radon proposed by Leggett et al.(32) was used to calculate committed effective doses following ingestion of radon. The model is based largely on the theoretical considerations, but also included some empirical features and simplifications. In the model, it is assumed that radon gas does not diffuse from stomach contents to stomach wall, but that radon is absorbed to blood solely via the small intestine. The effective dose per intake of ingested 222Rn is 6.9·10−7 mSv/Bq(6). This is the first time that an ingestion dose coefficient for radon has been published by the ICRP. If the standard assumptions for calculating guidance levels for radionuclides in drinking water are applied to radon (i.e. estimated daily intake is 2 litres of water, and all water contains the same concentration of the radionuclide in question) and the new radon ingestion dose coefficient is used (6.9·10−7 mSv/Bq), a radon concentration of 200 Bq/l in drinking water will result an annual ingestion dose of 0.1 mSv, which is the individual dose criterion recommended by WHO(5). However, as discussed earlier, the standard assumption for intake does not hold, as normal practices will have a significant effect on the amount of radon that remains dissolved in water after it leaves the tap, and dose estimates that do not take this into account will overestimate intake and therefore risk. When calculating ingestion dose from radon in water, only the amount of cold water directly ingested from the tap should be taken into consideration. As indicated in Table 2, this amount is significantly less than 1 litre per day in most cases. Taking the average cold water consumption rate of all studies listed in Table 2, 0.7 l/day, or 256 l/year, the radon concentration that corresponds to the WHO dose criterion is 566 Bq/l. MANAGING RADON IN DRINKING WATER In some parts of the world, a significant portion of the population relies on private well water (see example of countries in the Arctic region in Table 3) and, as shown in Table 1, radon concentrations in wells can be high. Guidance specifically for managing ingestion dose could be useful in these cases. Table 3. Examples of percentage of population on private well water. Country Population on private well (%) Reference Canada 11 Statistics Canada(33) Finland 17 Vesterbacka et al.(15) Norway 10 Jensen et al.(34) Sweden 15 Ek et al.(35) Country Population on private well (%) Reference Canada 11 Statistics Canada(33) Finland 17 Vesterbacka et al.(15) Norway 10 Jensen et al.(34) Sweden 15 Ek et al.(35) Table 3. Examples of percentage of population on private well water. Country Population on private well (%) Reference Canada 11 Statistics Canada(33) Finland 17 Vesterbacka et al.(15) Norway 10 Jensen et al.(34) Sweden 15 Ek et al.(35) Country Population on private well (%) Reference Canada 11 Statistics Canada(33) Finland 17 Vesterbacka et al.(15) Norway 10 Jensen et al.(34) Sweden 15 Ek et al.(35) Table 4 (third column) shows some examples of radon concentrations that correspond to the WHO individual dose criterion of 0.1 mSv/year, calculated using country-specific cold-water consumption rates. It is clear that local behaviours and consumption rates significantly impact what might be considered an ‘acceptable’ radon concentration for drinking water, when considering ingestion dose compared to the WHO dose criterion. It is also clear that guidance levels calculated based on radon ingestion could be much lower than recommendations based on estimates of outgassing and subsequent inhalation with regards to national indoor radon guideline (such as 2000 Bq/l in Canadian Drinking Water Guidelines(4)), except in cases where cold water consumption rates are very low (such as 0.18 l/d in the Netherlands). Table 4. Calculated concentrations of radon in drinking water that correspond to an annual dose of 0.1 mSv (WHO individual dose criterion), the contribution to radon concentration in indoor air and associated inhalation dose. Country Consumption rate (cold tap water, l/d) Radon in water (Bq/l) at 0.1 mSv/year Contribution to radon in air (Bq/m3) Associated inhalation dose (mSv/year)a Canada 1.2 331 33.1 1.6 Finland 0.5 794 79.4 3.7 Norway 0.58 685 68.5 3.2 Sweden 0.86 462 46.2 2.2 USA 0.92 432 43.2 2.0 Netherlands 0.18 2206 220.6 10.3 Country Consumption rate (cold tap water, l/d) Radon in water (Bq/l) at 0.1 mSv/year Contribution to radon in air (Bq/m3) Associated inhalation dose (mSv/year)a Canada 1.2 331 33.1 1.6 Finland 0.5 794 79.4 3.7 Norway 0.58 685 68.5 3.2 Sweden 0.86 462 46.2 2.2 USA 0.92 432 43.2 2.0 Netherlands 0.18 2206 220.6 10.3 aUsing radon inhalation dose conversion coefficient(6) of 6.7·10−6 mSv(Bq h m−3)−1. Table 4. Calculated concentrations of radon in drinking water that correspond to an annual dose of 0.1 mSv (WHO individual dose criterion), the contribution to radon concentration in indoor air and associated inhalation dose. Country Consumption rate (cold tap water, l/d) Radon in water (Bq/l) at 0.1 mSv/year Contribution to radon in air (Bq/m3) Associated inhalation dose (mSv/year)a Canada 1.2 331 33.1 1.6 Finland 0.5 794 79.4 3.7 Norway 0.58 685 68.5 3.2 Sweden 0.86 462 46.2 2.2 USA 0.92 432 43.2 2.0 Netherlands 0.18 2206 220.6 10.3 Country Consumption rate (cold tap water, l/d) Radon in water (Bq/l) at 0.1 mSv/year Contribution to radon in air (Bq/m3) Associated inhalation dose (mSv/year)a Canada 1.2 331 33.1 1.6 Finland 0.5 794 79.4 3.7 Norway 0.58 685 68.5 3.2 Sweden 0.86 462 46.2 2.2 USA 0.92 432 43.2 2.0 Netherlands 0.18 2206 220.6 10.3 aUsing radon inhalation dose conversion coefficient(6) of 6.7·10−6 mSv(Bq h m−3)−1. Using transfer coefficient(1) of 1.0 × 10−4, contributions of radon in water to radon concentration in the indoor air are given in fourth column of Table 4. Even for limiting radon ingestion dose at 0.1 mSv/year, radon in water can add significant amount of radon to indoor air, and the associated additional radon inhalation doses (last column in Table 4) are much higher than the radon ingestion dose. The decision to establish a guidance level should be made when it is justified, not just because it is possible. Because inhalation is recognised as the most significant pathway for radon exposure, the WHO recommends establishing criteria for radon in drinking water based on national reference levels for radon in indoor air(5). However, populations reliant on private wells in some geological formations could exceed 0.1 mSv per year if people drink a significant amount of cold tap water regularly. 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Report, Annex D—Exposures to Radon and Thoron and Their Decay Products ( New York : United Nations ) ( 1982 ). 24 Government of Canada . Government of Canada Radon Guideline. 2007 . Available at: https://www.canada.ca/en/health-canada/services/environmental-workplace-health/radiation/radon/government-canada-radon-guideline.html. 25 Environmental Protection Agency (EPA) . Report to the United States Congress on radon in drinking water, multimedia risk and cost assessment of radon. EPA 811-R-94-001. Washington DC. 1994 . 26 Roche , S. M. , Jones , A. Q. , Majowicz , S. E. , McEwen , S. A. and Pintar , K. D. M. Drinking water consumption patterns in Canadian communities (2001–2007) . J. Water Health 10 , 69 – 86 ( 2012 ). Google Scholar Crossref Search ADS PubMed 27 Gazan , R. , Sondey , J. , Maillot , M. , Guelinckx , I. and Lluch , A. Drinking water intake is associated with higher diet quality among French adults . Nutrients 8 ( 689 ), 1 – 23 ( 2016 ). 28 Mons , M. N. , van der Wielen , J. M. , Blokker , E. J. , Sinclair , M. I. , Hulshof , K. F. and Dangendorf , F. Estimation of the consumption of cold tap water for microbiological risk assessment: an overview of studies and statistical analysis of data . J. Water Health 5 ( Suppl 1 ), 151 – 170 ( 2007 ). Google Scholar Crossref Search ADS PubMed 29 Hanssen , O. J. , Rukke , E. O. , Saugen , B. , Kolstad , J. , Hafrom , P. , Krogh , L. , Raadal , H. L. , Ronning , A. and Wigum , K. S. The environmental effectiveness of the beverage sector in Norway in a factor 10 perspective . Life Cycle Manage. 12 , 257 – 265 ( 2007 ). Google Scholar Crossref Search ADS 30 Westrell , T. , Andersson , Y. and Stenstrom , T. A. Drinking water consumption patterns in Sweden . J. Water Health 4 , 511 – 522 ( 2006 ). Google Scholar Crossref Search ADS PubMed 31 Sebastian , R. S. , Enns , C. W. and Goldman , J. D. Drinking water intake in the U. S. What we eat in America, NHANES 2005-2008. Food Surveys Research Group, Dietary Data Brief No. 7. 2011 . Available at: https://www.ars.usda.gov/ARSUserFiles/80400530/pdf/DBrief/7_water_intakes_0508.pdf. Accessed 14 November 2018. 32 Leggett , R. W. , Marsh , J. W. , Gregoratto , D. and Blanchardon , E. A generic biokinetic model for noble gases with application to radon . J. Radiol. Prot. 33 , 413 – 432 ( 2013 ). Google Scholar Crossref Search ADS PubMed 33 Statistics Canada . Households and the environment survey, dwellings main source of water. 2018 . Available at: https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=3810027401. Accessed 14 November 2018. 34 Jensen , C. L. , Strand , T. , Ramberg , G. , Ruden , L. and Anestad , K. The Norwegian Radon Mapping and Remediation Program. 2004 . Available at: http://irpa11.irpa.net/pdfs/6a61.pdf. Accessed 14 November 2018. 35 Ek , B. M. , Thunholm , B. , Ostergren , I. , Falk , R. and Mjones , L. Naturally occurring radioactive elements, arsenic and other metals in drinking water from private drilled wells. SSI Rapport 2008:15. ISSN 0282-4434. 2008 . © Crown copyright 2019. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Protection Dosimetry Oxford University Press

A DISCUSSION ON ISSUES WITH RADON IN DRINKING WATER

Radiation Protection Dosimetry, Volume Advance Article – Mar 31, 2019

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Abstract

Abstract The majority of the world’s population relies on surface water or large public supply systems of groundwater, where radon is low and a guidance value for radon in drinking water is not necessary. However, the International Commission on Radiological Protection (ICRP) recently issued a dose coefficient for radon ingestion, raising questions among some radiation protection authorities about whether radon guidance values should be calculated for drinking water and how this might be done. Unlike many other radionuclides considered in drinking water management, radon has special characteristics and therefore requires special considerations. This note discusses some of these considerations, and also provides a brief review of radon concentrations measured in well-water supplies, especially private well-water systems, and cold tap water consumption rates reported in different countries. INTRODUCTION Radon (222Rn) is a chemically inert gas formed through the radioactive decay of 226Ra. Both are members of the 238U decay series. Uranium and radium occur naturally in soil and rocks, and provide a continuous source of radon. Radon can escape from the Earth’s crust and is present in the air everywhere in varying concentrations. Uranium, radium and radon can also dissolve in water and, therefore, may enter groundwater supplies that pass through radium-bearing rocks and soils. While water drawn from surface water supplies does not generally contain appreciable levels of radon, high radon concentrations are often observed in groundwater sources(1). Almost all radon management policies focus on radon in the air because radon inhalation is recognised as the largest contributor to background radiation dose. Health risks posed by ingesting radon in drinking water are thought to be insignificant compared to the risks posed by the transfer of radon into air through outgassing and its subsequent inhalation(2–4). An evaluation of international research data(2) has concluded that, on average, 90% of the dose attributable to radon in drinking water comes from inhalation rather than ingestion. Because of this, many drinking water guidelines do not include a guidance value for radon, or base their recommendations on risks of contributing to the indoor air concentration and resulting inhalation hazard(3, 4). For example, in the recent publication on the management of radioactivity in drinking water(5), WHO elected not to provide guidance level for radon in drinking water because it is considered more appropriate to measure and manage radon concentrations in indoor air. The International Commission on Radiological Protection (ICRP) recently issued a dose coefficient for radon ingestion(6), raising questions among some radiation protection authorities about whether radon guidance values for drinking water should be calculated and how this might be done. Unlike many other radionuclides considered in drinking water management, radon has special characteristics and therefore requires special considerations. This paper discusses some of these considerations, and also provides a brief review of radon concentrations measured in well-water supplies, especially private well-water systems, as reported in the published literature. RADON LEVELS IN GROUNDWATER SOURCES The most common conclusions of the studies on radon in groundwater and public water supplies in the USA suggest that the highest radon concentrations generally occur in portions of Appalachian Mountains, Rocky Mountains, and Basin and Range where uranium-bearing metamorphosed rocks, volcanics, and granite intrusive rocks are predominantly found(1). Private well sources and small public water supplies tend to have more radon than large public water supplies because they are often drawn from aquifers with low capacity. When these types of aquifers are uranium-bearing granite, metamorphic rocks, or fault zones, the radon concentration in the water tends to be high. Large public water supplies tend to use high-capacity sand and gravel aquifers, which are generally comprised of low-uranium rocks and sediments and tend to be lower in radon. The radon concentrations in the large public water supply systems of Canadian cities are very low; for example, less than 10 Bq/l in Ottawa, and below detection limits in Vancouver(7). A brief summary of radon concentrations in drinking water from well water or ground water sources is given in Table 1. The measured results show clearly that groundwater that passes through radium-bearing rocks and soils can have high radon concentrations; however, the variation is large. In Canada, an average radon concentration of 600 Bq/l was observed in well water of 16 schools in Nova Scotia while a median radon concentration of 9 Bq/l was found in 198 wells in the province of Quebec. In Finland, the average radon concentration was 50 Bq/l in dug wells, but about 10 times higher in drilled wells. A survey of 1604 groundwater samples from Norwegian crystalline bedrock aquifers showed that 14% wells had radon concentration above 500 Bq/l and a maximum radon concentration of 31 900 Bq/l was observed. Table 1. Radon concentrations in groundwater or well water measured in various locations (arithmetic mean (AM), median, range and other reported characteristics). Location # Samples Radon concentration Reference Curitiba, Brazil 31 AM = 44 Bq/l; 1.6–251 Bq/l Correa et al.(8) Rio de Janeiro, Brazil 88 AM < 3 Bq/l; < 3–75 Bq/l Almeida et al.(9) Nova Scotia, Canada 16 AM = 600 Bq/l; 120–1400 Bq/l Drage et al.(10, 11) Quebec, Canada 198 Median = 9 Bq/l; 0.2–310 Bq/l; 90% < 100 Bq/l Pinti et al.(12) Fujian, China 552 AM = 229 Bq/l; 0.7–3735 Bq/l Zhuo et al.(13) Czech 300 AM = 87 Bq/l; 5–1600 Bq/l Otahal et al.(14) Finland 184 (dug wells) AM = 50 Bq/l; max = 710 Bq/l Vesterbacka et al.(15) 288 (drilled wells) AM = 460 Bq/l; max = 8600 Bq/l; 10% > 1000 Bq/l Busan, Korea 439 AM = 36 Bq/l; 0–300 Bq/l Cho et al.(16) Norway 1604 (bedrock) 14% > 500 Bq/l; max = 31 900 Bq/l Banks et al.(17) 72 Median = 22 Bq/l; <10–410 Bq/l Banks et al.(18) Southern Greater Poland 89 AM = 2.7 Bq/l; 0.4–10.5 Bq/l Bem et al.(19) Karkonosze, Poland 199 AM = 212 Bq/l; 0.3–1392 Bq/l Przylibski and Gorecka(20) Spain 350 AM = 111 Bq/l; 35% > 100 Bq/l Lopez and Sanchez(21) Sweden 328 (drilled wells) AM = 573 Bq/l; 5–8105 Bq/l; 80% > 100 Bq/l Salih et al.(22) Location # Samples Radon concentration Reference Curitiba, Brazil 31 AM = 44 Bq/l; 1.6–251 Bq/l Correa et al.(8) Rio de Janeiro, Brazil 88 AM < 3 Bq/l; < 3–75 Bq/l Almeida et al.(9) Nova Scotia, Canada 16 AM = 600 Bq/l; 120–1400 Bq/l Drage et al.(10, 11) Quebec, Canada 198 Median = 9 Bq/l; 0.2–310 Bq/l; 90% < 100 Bq/l Pinti et al.(12) Fujian, China 552 AM = 229 Bq/l; 0.7–3735 Bq/l Zhuo et al.(13) Czech 300 AM = 87 Bq/l; 5–1600 Bq/l Otahal et al.(14) Finland 184 (dug wells) AM = 50 Bq/l; max = 710 Bq/l Vesterbacka et al.(15) 288 (drilled wells) AM = 460 Bq/l; max = 8600 Bq/l; 10% > 1000 Bq/l Busan, Korea 439 AM = 36 Bq/l; 0–300 Bq/l Cho et al.(16) Norway 1604 (bedrock) 14% > 500 Bq/l; max = 31 900 Bq/l Banks et al.(17) 72 Median = 22 Bq/l; <10–410 Bq/l Banks et al.(18) Southern Greater Poland 89 AM = 2.7 Bq/l; 0.4–10.5 Bq/l Bem et al.(19) Karkonosze, Poland 199 AM = 212 Bq/l; 0.3–1392 Bq/l Przylibski and Gorecka(20) Spain 350 AM = 111 Bq/l; 35% > 100 Bq/l Lopez and Sanchez(21) Sweden 328 (drilled wells) AM = 573 Bq/l; 5–8105 Bq/l; 80% > 100 Bq/l Salih et al.(22) Table 1. Radon concentrations in groundwater or well water measured in various locations (arithmetic mean (AM), median, range and other reported characteristics). Location # Samples Radon concentration Reference Curitiba, Brazil 31 AM = 44 Bq/l; 1.6–251 Bq/l Correa et al.(8) Rio de Janeiro, Brazil 88 AM < 3 Bq/l; < 3–75 Bq/l Almeida et al.(9) Nova Scotia, Canada 16 AM = 600 Bq/l; 120–1400 Bq/l Drage et al.(10, 11) Quebec, Canada 198 Median = 9 Bq/l; 0.2–310 Bq/l; 90% < 100 Bq/l Pinti et al.(12) Fujian, China 552 AM = 229 Bq/l; 0.7–3735 Bq/l Zhuo et al.(13) Czech 300 AM = 87 Bq/l; 5–1600 Bq/l Otahal et al.(14) Finland 184 (dug wells) AM = 50 Bq/l; max = 710 Bq/l Vesterbacka et al.(15) 288 (drilled wells) AM = 460 Bq/l; max = 8600 Bq/l; 10% > 1000 Bq/l Busan, Korea 439 AM = 36 Bq/l; 0–300 Bq/l Cho et al.(16) Norway 1604 (bedrock) 14% > 500 Bq/l; max = 31 900 Bq/l Banks et al.(17) 72 Median = 22 Bq/l; <10–410 Bq/l Banks et al.(18) Southern Greater Poland 89 AM = 2.7 Bq/l; 0.4–10.5 Bq/l Bem et al.(19) Karkonosze, Poland 199 AM = 212 Bq/l; 0.3–1392 Bq/l Przylibski and Gorecka(20) Spain 350 AM = 111 Bq/l; 35% > 100 Bq/l Lopez and Sanchez(21) Sweden 328 (drilled wells) AM = 573 Bq/l; 5–8105 Bq/l; 80% > 100 Bq/l Salih et al.(22) Location # Samples Radon concentration Reference Curitiba, Brazil 31 AM = 44 Bq/l; 1.6–251 Bq/l Correa et al.(8) Rio de Janeiro, Brazil 88 AM < 3 Bq/l; < 3–75 Bq/l Almeida et al.(9) Nova Scotia, Canada 16 AM = 600 Bq/l; 120–1400 Bq/l Drage et al.(10, 11) Quebec, Canada 198 Median = 9 Bq/l; 0.2–310 Bq/l; 90% < 100 Bq/l Pinti et al.(12) Fujian, China 552 AM = 229 Bq/l; 0.7–3735 Bq/l Zhuo et al.(13) Czech 300 AM = 87 Bq/l; 5–1600 Bq/l Otahal et al.(14) Finland 184 (dug wells) AM = 50 Bq/l; max = 710 Bq/l Vesterbacka et al.(15) 288 (drilled wells) AM = 460 Bq/l; max = 8600 Bq/l; 10% > 1000 Bq/l Busan, Korea 439 AM = 36 Bq/l; 0–300 Bq/l Cho et al.(16) Norway 1604 (bedrock) 14% > 500 Bq/l; max = 31 900 Bq/l Banks et al.(17) 72 Median = 22 Bq/l; <10–410 Bq/l Banks et al.(18) Southern Greater Poland 89 AM = 2.7 Bq/l; 0.4–10.5 Bq/l Bem et al.(19) Karkonosze, Poland 199 AM = 212 Bq/l; 0.3–1392 Bq/l Przylibski and Gorecka(20) Spain 350 AM = 111 Bq/l; 35% > 100 Bq/l Lopez and Sanchez(21) Sweden 328 (drilled wells) AM = 573 Bq/l; 5–8105 Bq/l; 80% > 100 Bq/l Salih et al.(22) CHARACTERISTICS OF RADON IN WATER Radon is fairly soluble in water, with its solubility decreasing rapidly with increasing temperature. The coefficient of radon solubility as a function of water temperature is shown in Figure 1. One can see clearly that radon will escape to the air during normal household activities, such as cooking. Figure 1. View largeDownload slide Coefficients of radon solubility in water as a function of water temperature (data taken from UNSCEAR 1982 Report(23)). Figure 1. View largeDownload slide Coefficients of radon solubility in water as a function of water temperature (data taken from UNSCEAR 1982 Report(23)). Radon is also extremely volatile and readily released from water into air. It can escape from water even when running water from the tap to a container before drinking. In situations where water is both heated and agitated, such as boiling water for tea, it is assumed that most of the radon ends up in the air. The US Committee on Risk Assessment of Exposure to Radon in Drinking Water assessed the transfer of radon from water to indoor air(1) from a range of household activities, including showering and dishwashing. It showed that there is reasonable agreement between the average value of transfer coefficient estimated by the models and the value calculated from measured data, which led to a recommendation of 1.0 × 10−4 as the best central estimate of the transfer coefficient. Based on this transfer coefficient and the Canadian action level for radon in indoor air (200 Bq/m3)(24), the Canadian Drinking Water Guidelines(4) recommend that actions be taken to manage radon in water if the concentration exceeds 2000 Bq/l. The fact that radon readily outgases from water makes water treatment relatively easy. Public water supply systems can easily reduce radon in water by various aeration methods, with removal efficiency from at least 70% to more than 99%(1). COLD WATER CONSUMPTION Due to the characteristics of radon in water described above, the ingestion dose from radon will depend on how the water is consumed, and will be almost entirely from cold water directly ingested from the tap (rather than water that is heated, boiled or otherwise treated). Based on data collected by the US Department of Agriculture 1977-1978 Nationwide Food Consumption Survey, the estimated mean value of daily water intake was 1.2 l/day for all uses of tap water which consists of both direct use (i.e. direct ingestion) and indirect use (i.e. making coffee, tea, etc)(1). The US EPA has estimated that slightly more than half of the tap water used is directly ingested, or about 0.6 l/day for direct use(25). A pooled analysis of seven cross-sectional studies from Newfoundland and Labrador, Waterloo and Hamilton Regions, Ontario and Vancouver, East Kootenay and Northern Interior Regions, British Columbia (2001–2007) was performed to investigate the drinking water consumption patterns of Canadians and to identify factors associated with the volume of tap water consumed(26). Tap water was defined as water directly from the tap with no subsequent treatment. The mean volume of tap water consumed among 6325 tap water users was 1.2 ± 0.8 l/day. A brief summary of surveys on daily consumption of cold tap water in seven countries is given in Table 2. The average cold water consumption rate varied from 0.18 to 1.2 l/day with an overall average of 0.7 l/day. In all seven countries, the mean daily volume of cold water consumed was significantly lower than the default assumption of 2 l/day that is often used when calculating guidance levels. However, it is clear that daily consumption of water can vary with the amount of physical activity performed by an individual as well as with fluctuations in temperature and humidity. For example, people may drink more in summer than in winter, and people who live in warmer climates might have higher intakes of water. Table 2. Daily consumption of cold tap water (litres). Country Daily consumption of cold tap water (l) Note Reference Canada 1.2 ± 0.8 n = 6325; highly variable 0.03–9.0 l/day; highest for ages 18-29 y, lower in older ages; females (>29 y) drank more than males Roche et al.(26) Finland 0.5 0.5 l/day for radon, 2.2 l/day for all other radionuclides when calculating ingestion dose Vesterbacka et al.(15) France 0.8 ± 0.6 n = 1918; women consumed more cold tap water than men. Gazan et al.(27) Netherlands 0.18 n = 6250 Mons et al.(28) Norway 0.58 Hanssen et al.(29) Sweden 0.86 ± 0.48 n = 11189; women consumed more cold tap water than men; cold tap water intake was highest in oldest age group (>70 yrs) Westrell et al.(30) USA 0.92 n = 16,566; vary widely 0–2.3 l/day; women drink more plain tap water than men for all age groups Sebastian et al.(31) Country Daily consumption of cold tap water (l) Note Reference Canada 1.2 ± 0.8 n = 6325; highly variable 0.03–9.0 l/day; highest for ages 18-29 y, lower in older ages; females (>29 y) drank more than males Roche et al.(26) Finland 0.5 0.5 l/day for radon, 2.2 l/day for all other radionuclides when calculating ingestion dose Vesterbacka et al.(15) France 0.8 ± 0.6 n = 1918; women consumed more cold tap water than men. Gazan et al.(27) Netherlands 0.18 n = 6250 Mons et al.(28) Norway 0.58 Hanssen et al.(29) Sweden 0.86 ± 0.48 n = 11189; women consumed more cold tap water than men; cold tap water intake was highest in oldest age group (>70 yrs) Westrell et al.(30) USA 0.92 n = 16,566; vary widely 0–2.3 l/day; women drink more plain tap water than men for all age groups Sebastian et al.(31) Table 2. Daily consumption of cold tap water (litres). Country Daily consumption of cold tap water (l) Note Reference Canada 1.2 ± 0.8 n = 6325; highly variable 0.03–9.0 l/day; highest for ages 18-29 y, lower in older ages; females (>29 y) drank more than males Roche et al.(26) Finland 0.5 0.5 l/day for radon, 2.2 l/day for all other radionuclides when calculating ingestion dose Vesterbacka et al.(15) France 0.8 ± 0.6 n = 1918; women consumed more cold tap water than men. Gazan et al.(27) Netherlands 0.18 n = 6250 Mons et al.(28) Norway 0.58 Hanssen et al.(29) Sweden 0.86 ± 0.48 n = 11189; women consumed more cold tap water than men; cold tap water intake was highest in oldest age group (>70 yrs) Westrell et al.(30) USA 0.92 n = 16,566; vary widely 0–2.3 l/day; women drink more plain tap water than men for all age groups Sebastian et al.(31) Country Daily consumption of cold tap water (l) Note Reference Canada 1.2 ± 0.8 n = 6325; highly variable 0.03–9.0 l/day; highest for ages 18-29 y, lower in older ages; females (>29 y) drank more than males Roche et al.(26) Finland 0.5 0.5 l/day for radon, 2.2 l/day for all other radionuclides when calculating ingestion dose Vesterbacka et al.(15) France 0.8 ± 0.6 n = 1918; women consumed more cold tap water than men. Gazan et al.(27) Netherlands 0.18 n = 6250 Mons et al.(28) Norway 0.58 Hanssen et al.(29) Sweden 0.86 ± 0.48 n = 11189; women consumed more cold tap water than men; cold tap water intake was highest in oldest age group (>70 yrs) Westrell et al.(30) USA 0.92 n = 16,566; vary widely 0–2.3 l/day; women drink more plain tap water than men for all age groups Sebastian et al.(31) RADON INGESTION DOSE In the recent ICRP Publication 137(6), a new biokinetic model for systemic radon proposed by Leggett et al.(32) was used to calculate committed effective doses following ingestion of radon. The model is based largely on the theoretical considerations, but also included some empirical features and simplifications. In the model, it is assumed that radon gas does not diffuse from stomach contents to stomach wall, but that radon is absorbed to blood solely via the small intestine. The effective dose per intake of ingested 222Rn is 6.9·10−7 mSv/Bq(6). This is the first time that an ingestion dose coefficient for radon has been published by the ICRP. If the standard assumptions for calculating guidance levels for radionuclides in drinking water are applied to radon (i.e. estimated daily intake is 2 litres of water, and all water contains the same concentration of the radionuclide in question) and the new radon ingestion dose coefficient is used (6.9·10−7 mSv/Bq), a radon concentration of 200 Bq/l in drinking water will result an annual ingestion dose of 0.1 mSv, which is the individual dose criterion recommended by WHO(5). However, as discussed earlier, the standard assumption for intake does not hold, as normal practices will have a significant effect on the amount of radon that remains dissolved in water after it leaves the tap, and dose estimates that do not take this into account will overestimate intake and therefore risk. When calculating ingestion dose from radon in water, only the amount of cold water directly ingested from the tap should be taken into consideration. As indicated in Table 2, this amount is significantly less than 1 litre per day in most cases. Taking the average cold water consumption rate of all studies listed in Table 2, 0.7 l/day, or 256 l/year, the radon concentration that corresponds to the WHO dose criterion is 566 Bq/l. MANAGING RADON IN DRINKING WATER In some parts of the world, a significant portion of the population relies on private well water (see example of countries in the Arctic region in Table 3) and, as shown in Table 1, radon concentrations in wells can be high. Guidance specifically for managing ingestion dose could be useful in these cases. Table 3. Examples of percentage of population on private well water. Country Population on private well (%) Reference Canada 11 Statistics Canada(33) Finland 17 Vesterbacka et al.(15) Norway 10 Jensen et al.(34) Sweden 15 Ek et al.(35) Country Population on private well (%) Reference Canada 11 Statistics Canada(33) Finland 17 Vesterbacka et al.(15) Norway 10 Jensen et al.(34) Sweden 15 Ek et al.(35) Table 3. Examples of percentage of population on private well water. Country Population on private well (%) Reference Canada 11 Statistics Canada(33) Finland 17 Vesterbacka et al.(15) Norway 10 Jensen et al.(34) Sweden 15 Ek et al.(35) Country Population on private well (%) Reference Canada 11 Statistics Canada(33) Finland 17 Vesterbacka et al.(15) Norway 10 Jensen et al.(34) Sweden 15 Ek et al.(35) Table 4 (third column) shows some examples of radon concentrations that correspond to the WHO individual dose criterion of 0.1 mSv/year, calculated using country-specific cold-water consumption rates. It is clear that local behaviours and consumption rates significantly impact what might be considered an ‘acceptable’ radon concentration for drinking water, when considering ingestion dose compared to the WHO dose criterion. It is also clear that guidance levels calculated based on radon ingestion could be much lower than recommendations based on estimates of outgassing and subsequent inhalation with regards to national indoor radon guideline (such as 2000 Bq/l in Canadian Drinking Water Guidelines(4)), except in cases where cold water consumption rates are very low (such as 0.18 l/d in the Netherlands). Table 4. Calculated concentrations of radon in drinking water that correspond to an annual dose of 0.1 mSv (WHO individual dose criterion), the contribution to radon concentration in indoor air and associated inhalation dose. Country Consumption rate (cold tap water, l/d) Radon in water (Bq/l) at 0.1 mSv/year Contribution to radon in air (Bq/m3) Associated inhalation dose (mSv/year)a Canada 1.2 331 33.1 1.6 Finland 0.5 794 79.4 3.7 Norway 0.58 685 68.5 3.2 Sweden 0.86 462 46.2 2.2 USA 0.92 432 43.2 2.0 Netherlands 0.18 2206 220.6 10.3 Country Consumption rate (cold tap water, l/d) Radon in water (Bq/l) at 0.1 mSv/year Contribution to radon in air (Bq/m3) Associated inhalation dose (mSv/year)a Canada 1.2 331 33.1 1.6 Finland 0.5 794 79.4 3.7 Norway 0.58 685 68.5 3.2 Sweden 0.86 462 46.2 2.2 USA 0.92 432 43.2 2.0 Netherlands 0.18 2206 220.6 10.3 aUsing radon inhalation dose conversion coefficient(6) of 6.7·10−6 mSv(Bq h m−3)−1. Table 4. Calculated concentrations of radon in drinking water that correspond to an annual dose of 0.1 mSv (WHO individual dose criterion), the contribution to radon concentration in indoor air and associated inhalation dose. Country Consumption rate (cold tap water, l/d) Radon in water (Bq/l) at 0.1 mSv/year Contribution to radon in air (Bq/m3) Associated inhalation dose (mSv/year)a Canada 1.2 331 33.1 1.6 Finland 0.5 794 79.4 3.7 Norway 0.58 685 68.5 3.2 Sweden 0.86 462 46.2 2.2 USA 0.92 432 43.2 2.0 Netherlands 0.18 2206 220.6 10.3 Country Consumption rate (cold tap water, l/d) Radon in water (Bq/l) at 0.1 mSv/year Contribution to radon in air (Bq/m3) Associated inhalation dose (mSv/year)a Canada 1.2 331 33.1 1.6 Finland 0.5 794 79.4 3.7 Norway 0.58 685 68.5 3.2 Sweden 0.86 462 46.2 2.2 USA 0.92 432 43.2 2.0 Netherlands 0.18 2206 220.6 10.3 aUsing radon inhalation dose conversion coefficient(6) of 6.7·10−6 mSv(Bq h m−3)−1. Using transfer coefficient(1) of 1.0 × 10−4, contributions of radon in water to radon concentration in the indoor air are given in fourth column of Table 4. Even for limiting radon ingestion dose at 0.1 mSv/year, radon in water can add significant amount of radon to indoor air, and the associated additional radon inhalation doses (last column in Table 4) are much higher than the radon ingestion dose. The decision to establish a guidance level should be made when it is justified, not just because it is possible. Because inhalation is recognised as the most significant pathway for radon exposure, the WHO recommends establishing criteria for radon in drinking water based on national reference levels for radon in indoor air(5). However, populations reliant on private wells in some geological formations could exceed 0.1 mSv per year if people drink a significant amount of cold tap water regularly. 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Naturally occurring radioactive elements, arsenic and other metals in drinking water from private drilled wells. SSI Rapport 2008:15. ISSN 0282-4434. 2008 . © Crown copyright 2019. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

Journal

Radiation Protection DosimetryOxford University Press

Published: Mar 31, 2019

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