A Bayesian analysis or scientific judgment of uncertainties in estimating risk due to 222Rn in U.S. public drinking water supplies

The elements which contribute to the range of values or uncertainties for the lifetime risk and dose equivalent due to 222Rn in U.S. public drinking water supplies are estimated and discussed here. From imperfect scientific knowledge, reasonable upper and lower bounds are placed on these estimates through the use of a semiquantitative Bayesian approach to uncertainty analysis. The factors considered are: occurrence of 222Rn in drinking water, indoor air 222Rn concentrations as a function of drinking water concentration, equilibrium state of the progeny, fraction of daughter products attached to aerosol particles, anatomical and dosimetric variables, epidemiological studies and choice of latency period, plateau period and effects of age. For Rn in U.S. public drinking water supplies, it is estimated that the best estimate for the lifetime lung cancer risk factor is 5 X 10(-9) excess cases of lung cancer per becquerel of Rn per m3 of water (2 X 10(-7) excess cases of lung cancer per picocurie of Rn per liter of water), with an estimated range between 2 X 10(-9) and 2 X 10(-8) excess cases per becquerel of Rn per m3 of water (5 X 10(-8) and 7 X 10(-7) excess cases per picocurie of Rn per liter). The best estimate of the lifetime population risk due to 222Rn in U.S. public drinking water supplies is estimated to be 6,000 excess lung cancers, with a reasonable range of 1,000 to 30,000.     

Estimation of the radiological risk related to the presence of radon 222 in a hydrotherapy centre in Tunisia.

The (222)Rn concentration in air was measured in a thermal water spa used as a hydrotherapy centre in Tunisia. The associated health risk for employees and patients due to the inhalation of (222)Rn and its progeny was estimated. A protection scheme for the employees of the spas has been designed. Results show that the (222)Rn concentration varies in the range 33-589 Bq m(-3). The (222)Rn concentrations measured in the present study show lower values in comparison to those reported for thermal spas in other countries. The (222)Rn concentration in different rooms of the spa depends mainly on the ventilation rate. A model based on a dosimetric approach was adopted to estimate the radon risk considering the (222)Rn concentration, the time spent in the spa, and the radioactive equilibrium factor F. The annual effective dose was found to vary between 0.2 and 1.7 mSv for workers while the range for patients was from 2.8 x 10(-4) to 1.1 x 10(-4) mSv. These values are within the ICRP recommended values.     

Study of radon daughter concentrations in Polk and Hillsborough counties

The present study finds the average excess dose equivalent resulting from external gamma radiation on reclaimed land to be 17 mrem/yr (whole body); the highest excess is 166 mrem/yr, well below the NCRP limit that might be compared (500 mrem/yr). In contrast, the annual average excess exposure from radon-daughter inhalation on reclaimed land has been found to be 540 mrem/yr to the whole lung, more than twice that resulting from natural background in the study area and more than 5 times the national average dose equivalent reported in NCRP 45 (100 mrem/yr). Moreover, a significant number of individuals presently receive lung doses exceeding limits inferred from NCRP recommendations. These results indicate the need for corrective action to reduce radiation exposure of members of the general population whose exposure exceeds dose limiting recommendations and possibly to reduce radiation exposures well below these limits, thereby lowering risks even further.     

Radon 222 in drinking water from Jelenia Gora area]

In the last decade one can observe an increasing interest in the study of 222Rn levels in water samples. In Poland, radon concentration is measured continuously and routinely only in mineral and medical waters from springs located in the area of health resorts in the Sudety Mountains. The reason for these studies is the fact that waters present in this area have a high radon concentration. Radon--222 concentration in surface water, wells water and tap water in Jelenia Góra has been quantitative determined. The measurements were performed using the alpha liquid scintillation counting method. "Grabarów", the main waterworks in Jelenia Góra is supplied with the mixed water consisting from the surface water (river Bóbr), which main characteristic is low radon concentration (below 11 Bq/l), and from ground water with the radon concentration from 179.6 Bq/l to 289.0 Bq/l in it. Also, waterworks "Ceglana", "Pod Karpaczem", "Sniezne Kot?y" is supplied with the ground water have a high radon concentration: from 93.2 Bq/l to 216.4 Bq/l. The next waterworks: "Podgórzyn", "Le?niczówka", "Kamienna Wieza", "Górzyniec" and "Centrum-Jelchem" is supplied with the surface water in which the radon concentration is low: from 1.1 Bq/l to 7.5 Bq/l. The annual effective dose to an individual from an intake of radon-222 via ingestion of drinking water is calculated by the Crawford-Brown's biokinetic model. In the present study it was found to be about 0.9 mSv/y (222Rn concentration level in drinking waters about 200 Bq/l).     

Internal dose assessment of natural uranium from drinking water based on biokinetic modeling and individual bioassay monitoring: a study of a Finnish family

Since the later 1960's, a nationwide survey on natural radionuclides in drinking water showed high concentrations of natural uranium (U) in Finland, especially in uraniferous granite areas. In order to assess the radiation dose from the natural uranium to individuals, the concentrations of natural uranium in drinking water of the drilled wells were determined by radiochemical and alpha spectrometric methods. Uranium contents were measured in the urinary samples of five members of a Finnish family by means of inductively coupled plasma-mass spectrometry. Correspondingly, theoretical biokinetic modeling of natural uranium incorporated for the same persons were performed with the aid of follow-up interviews. The ICRP biokinetic compartmental model and the age-dependent transfer rates for uranium were used to model the intake, transfer, distribution, retention, and excretion of (234)U and (238)U, respectively, from the drinking water for each person of the family. The organ absorbed dose, equivalent dose, and effective dose were evaluated for each family member at time intervals using specific effective energy values calculated by the SEECAL program and compared with recommended values. The modeled urinary excretion rates were found to be mostly higher than the measured values by a factor of three. The mean annual effective dose for this family is 8 muSv y(-1). By comparing the measured and calculated data, estimation of retrospective radiation exposure based on biokinetic modeling and bioassay method is enhanced and, vice versa, the biokinetic and dosimetric models are tested and verified.     

A study on natural radioactivity in khewra salt mines, pakistan

The Khewra Salt Mines, the second largest salt mines in the world, are located 160 km south of Islamabad, the capital of Pakistan. Around 1000 workers are involved in the removal of salt from these mines. More than 40,000 visitors come annually to see the mines. The visitors and workers are directly exposed to the internal and external radiological hazards of radon and gamma rays in these mines. The general public is affected by the intake of the salt containing the naturally occurring radionuclides. Therefore the concentration of radon (²²²Rn) in the Khewra Salt Mines and activity concentrations of the naturally occurring radionuclides in the salt samples from these mines were measured. Both active and passive techniques were employed for the measurement of radon with Radon Alpha Detector (RAD-7) and SSNTD respectively. The concentration of ²²²Rn was 26 ± 4 Bq m^-3 measured by the active method while 43 ± 8 Bq m^-3 was measured by the passive method. The activity concentration of the radionuclides was measured using gamma ray spectrometry with HPGe detector. The mean activity of ⁴⁰K in salt samples was found to be 36 ± 20 Bq kg^-1 and the concentration of ²²⁶Ra and ²³²Th in the salt samples was below the detection limits. Gamma radiation hazard was assessed in terms of the external gamma dose from salt slabs and the rooms made of salt and the annual effective dose due to gamma radiation. The exposure to radon daughters, annual effective dose and excessive lifetime cancer risk due to radon in the mines were estimated. The mean annual effective dose due to an intake of ⁴⁰K from the salt was calculated as 20.0 ± 11.1 μSv, which is lower than the average annual effective dose rate of 0.29 mSv, received by the ingestion of natural radionuclides. Due to the low concentration values of primordial radionuclides in the salt and radon (²²²Rn) in the mines, a 'low level activity measurement laboratory' is suggested to be established in these mines.     

Analysis of uranium in drinking water samples using laser induced fluorimetry

Uranium concentration in drinking water samples collected from some areas of Punjab and Himachal Pradesh has been measured using a laser induced fluorimetry technique. The sources of water comprise hand pumps and tube wells. Uranium concentration in the water samples from Punjab varies from 1.39 +/- 0.16 to 98.25 +/- 2.06 ppb with a mean value of 19.84 +/- 0.87 ppb. The uranium concentration in most of the drinking water samples from Punjab exceeds the safe limit recommended by the World Health Organization. However, the uranium concentration in water samples from Himachal Pradesh is well within the recommended levels. The annual effective dose equivalent associated with drinking water due to uranium concentration is estimated from its annual intake using dosimetric information based on ICRP Report 72. The resulting value of the annual effective dose from drinking water sources is in the range of 0.13 to 81.59 muSv. The annual effective dose received by the population due to the consumption of drinking water from these areas is well within the recommended limit. In order to check the accuracy of the technique a few water samples were also analyzed using a fission track registration technique. A good agreement has been observed between the uranium values determined by these techniques.     

中国部分地区~(220)Rn浓度的测量

目的 了解我国不同地区室内外~(220)Rn及其子体的水平及对居民所产生的有效剂量。方法 采用日本名古屋大学提供人的Rn-Tn固体径迹探测器和子体潜能法测量了室内外~(222)Rn、~(220)Rn及其子体的浓度,用UNSCEAR 1996年报告给出的~(222)Rn、~(220)Rn剂量转换系数估算了吸入~(222)Rn和~(220)Rn子体产生的年均有效剂量。对土壤中~(232)Th含量与~(220)Rn浓度的相关性及其影响因素进行了探讨。结果 北京、广州、珠海、平凉等地室内~(220)Rn及其子体的浓度分别是相似文献   

Age-dependent lung doses from ingested 222Rn in drinking water

The U.S. Environmental Protection Agency currently is considering regulatory standards limiting the concentration of 222Rn in public drinking water supplies. As part of this effort, a criteria document has been prepared detailing the health risks expected to occur from the presence of 222Rn in water used in homes. The present report examines the dose equivalent delivered to lung tissue following direct ingestion of 222Rn in water. Irradiation from both in-situ decay of 222Rn in lung tissue and the decay of 222Rn in lung air passages following exhalation are examined and results presented for ages from neonate through adult. These results indicate that the risk of lung cancer from inhalation of airborne progeny following emanation of 222Rn from water into home air is significantly greater than the risk from both irradiation pathways considered in ingestion at all ages.     

Radiation doses to members of the U.S. population from ubiquitous radionuclides in the body: Part 3, results, variability, and uncertainty

This paper is Part 3 of a three-part series investigating effective dose rates to residents of the United States from intakes of ubiquitous radionuclides, including radionuclides occurring naturally, radionuclides whose concentrations are technologically enhanced, and anthropogenic radionuclides. The radionuclides of interest are the (238)U series (14 nuclides), the actinium series (headed by (235)U; 11 nuclides), and the (232)Th series (11 nuclides); primordial radionuclides (87)Rb and (40)K; cosmogenic and fallout radionuclides (14)C and (3)H; and purely anthropogenic radionuclides (137)Cs-(137m)Ba, (129)I and (90)Sr-(90)Y. This series of papers explicitly excludes intakes from inhaling (222)Rn, (220)Rn, and their short-lived decay products; it also excludes intakes of radionuclides in occupational and medical settings. In this work, it is assumed that instantaneous dose rates in target organs are proportional to steady-state radionuclide concentrations in source regions. Part 1 reviewed, summarized, characterized, and grouped all published and some unpublished data for U.S. residents on ubiquitous radionuclide concentrations in tissues and organs. Part 2 described the methods used to organize the data collected in Part 1 and segregate it into the ages and genders defined by the study, including imputed missing values from the existing data, apportioned activity in bone, and imputed activity in hollow organ contents and the remainder of the body. This paper estimates equivalent dose rates to target tissues from source regions and maps target tissues to lists of tissues with International Commission on Radiation Protection (ICRP) tissue-weighting factors or to surrogate tissue regions when there is no direct match. Effective dose rates using ICRP tissue-weighting factors recommended in 1977, 1990, and 2007, are then calculated, and an upper bound of variability of the effective dose rate is estimated by calculating the average coefficients of variation (CV), assuming all variance is due to variability. Most of the data were for adult males, whose average effective dose rate is estimated to be 337 μSv y(-1) (CV = 0.65, geometric mean = 283 μSv y(-1), geometric standard deviation s(G) = 1.81) using 2007 ICRP tissue-weighting factors. This result is between the National Council on Radiation Protection and Measurements' 1987 estimate of 390 μSv y(-1) (using 1977 w(T)s) and its 2009 estimate of 285 μSv y(-1) (using 2007 w(T)s) and is higher than the United Nations Scientific Committee on the Effects of Atomic Radiation's 2000 estimate of 310 μSv y(-1) (using 1990 w(T)s). The methods and software developed for this project are sufficiently detailed and sufficiently general to be usable with autopsy data from any or all countries.     

Uranium in vitro bioassay action level used to screen workers for chronic inhalation intakes of uranium mill tailings.

A uranium in vitro bioassay (urinalysis) action level was derived for use at the Department of Energy's Uranium Mill Tailings Remedial Action Project sites to identify chronic inhalation intakes of uranium mill tailings causing 0.5 mSv (50 mrem) annual effective dose equivalent. All radionuclides in the 238U decay chain that contribute 1% or more to the annual effective dose equivalent from an inhalation intake of uranium mill tailings were included in the derivation of the urinalysis action level. Using a chronic inhalation intake model, the uranium urinalysis action level for a 24-h urine sample, collected on a quarterly schedule, was calculated to be 1.5 micrograms.     

Population doses, excess deaths and loss of life expectancy from mass chest x-ray examinations in Japan--1980

The number of mass chest x-ray examinations in Japan in 1980 was 26.6 million and the average effective dose equivalent was 26 mrem per examination. The genetically significant dose was .017 mrem per person per year, the per caput mean marrow dose was 5.9 mrem, the leukemia significant dose was 5.2 mrem and the malignancy significant dose was 2.8 mrem. The excess deaths were calculated to be 70-280 depending on the risk model used. Those would be in excess to the 3.7 million cancer deaths normally expected among the examined population. The loss of life expectancy calculated with a relative risk model was 38 yr for males and 43 yr for females due to leukemia with a latent period of 2 yr and an expression period of 25 yr, and 12 yr for males and 14 yr for females due to other cancers with a latent period of 10 yr and an expression period of lifetime in the 20-24 age group.     

222Rn concentration in ground waters of coastal Karnataka and Kaiga of south west coast of India.

Groundwater (open well and bore well) samples from various locations of coastal Karnataka and Kaiga have been investigated for their 222Rn concentrations by emanometry method. The concentration of 222Rn in open well water was found to vary in the range 0.14-25.4 Bq L(-1) with a median value of 3.74 Bq L(-1) and that in bore well water in the range of 0.22-197.0 Bq L(-1) with a median value of 5.75 Bq L(-1). From the measured concentrations the effective doses for the population of the region were estimated. The effective dose was found to vary from 0.09 microSv y(-1) to 204.2 microSv y(-1) for open well water consumers and from 0.2 microSv y(-1) to 1586.9 microSv y(-1) for bore well water consumers. The results of the present study are also compared with the literature values and discussed.     

山东省矿泉水氡浓度的测定与卫生学评价

目的 摸清山东省矿泉水中²²²Rn浓度水平及变化规律,作出卫生学评价。方法 闪烁法测量矿泉水中²²²Rn浓度。结果 山东省矿泉水中²²²Rn浓度范围为0.51~807.20 Bq·L^-1,几何均值为22.09 Bq·L^-1,水中氡在自然放置条件下其残留率(P)与放置时间(T)呈P=46.666 T^-0.517(0.117 h ≤ T ≤ 9 h)函数关系。山东省矿泉水水中²²²Rn所致待积有效剂量为9.68×10^-2 mSv·a^-1。结论 饮用山东省矿泉水不致于对饮用者造成过多的剂量负担。     

Radon and thoron in cave dwellings (Yan'an, China)

222Rn and 220Rn concentrations were measured in cave dwellings and brick houses in the region of Yan'an (China) during summer 1997. The underground dwellings are built into Quaternary loess, and all investigated houses are founded on it. The median values of indoor 222Rn and 220Rn concentrations are 42 (n = 18) and 77 Bq m(-3) (n = 15) for brick houses and 92 (n = 23) and 215 (n = 17) Bq m(-3) for cave dwellings. To classify the dwellings in respect to their "cave-character," the fraction of walls having a direct contact to the loses is calculated for each dwelling. While the 222Rn concentrations are increasing with higher fractions, the 220Rn concentrations are not correlated with this fraction. On the other hand, due to the short half-life of 220Rn the distance from the measuring point to the walls is negatively correlated with the 220Rn concentration, while there is no correlation with the 222Rn concentration. Therefore, concentric isolines of 220Rn concentrations showing a strong gradient were detected in cave dwellings. An influence of the ventilation rate is distinct for 222Rn but weak for 220Rn. The effective dose rates for 222Rn and 220Rn and their progenies are calculated for brick houses (2.7 mSv y(-1)), cave dwellings (7.1 mSv y(-1)), and for traditional cave dwellings with a bed foundation built with loess (16.7 mSv y(-1)). These calculations are based on summer measurements only. It is expected that the true effective dose rates will be significantly higher.     

Radiological risk from consuming fish and wildlife to Native Americans on the Hanford Site (USA)

Historical operations at the Hanford Site (Washington State, USA) have released a wide array of non-radionuclide and radionuclide contaminants into the environment. As a result of stakeholder concerns, Native American exposure scenarios have been integrated into Hanford risk assessments. Because its contribution to radiological risk to Native Americans is culturally and geographically specific but quantitatively uncertain, a fish and wildlife ingestion pathway was examined in this study. Adult consumption rates were derived from 20 Native American scenarios (based on 12 studies) at Hanford, and tissue concentrations of key radionuclides in fish, game birds, and game mammals were compiled from the Hanford Environmental Information System (HEIS) database for a recent time interval (1995-2007) during the post-operational period. It was assumed that skeletal muscle comprised 90% of intake, while other tissues accounted for the remainder. Acknowledging data gaps, median concentrations of eight radionuclides (i.e., Co-60, Cs-137, Sr-90, Tc-99, U-234, U-238, Pu-238, and Pu-239/240) in skeletal muscle and other tissues were below 0.01 and 1 pCi/g wet wt, respectively. These radionuclide concentrations were not significantly different (Bonferroni P>0.05) on and off the Hanford Site. Despite no observed difference between onsite and offsite tissue concentrations, radiation dose and risk were calculated for the fish and wildlife ingestion pathway using onsite data. With median consumption rates and radionuclide tissue concentrations, skeletal muscle provided 42% of the dose, while other tissues (primarily bone and carcass) accounted for 58%. In terms of biota, fish ingestion was the largest contributor to dose (64%). Among radionuclides, Sr-90 was dominant, accounting for 47% of the dose. At median intake and radionuclide levels, estimated annual dose (0.36 mrem/yr) was below a dose limit of 15 mrem/yr recommended by the United States Environmental Protection Agency (USEPA), as well as below a dose limit of 100 mrem/yr proposed by the International Commission on Radiation Protection (ICRP). Similarly, lifetime cancer risk (1.7E−5), calculated with median inputs, was below risk levels corresponding to these dose limits. However, our dose and risk estimates apply to only one pathway within a multidimensional exposure scenario for Native Americans. On the other hand, radiation dose and risk corresponding to onsite tissue concentrations were not significantly different from those corresponding to offsite (background) concentrations. Recognizing uncertainties in exposure and toxicity assessments, our results may facilitate informed decision making and optimize resource allocation within a risk assessment framework at the Hanford Site.     

Regulatory consideration in radiation protection

A regulatory scheme is suggested that identifies regions labeled "unacceptable" and "safe" as the upper and lower bounds and "operational" region is identified as the continuum between the two extremes. These regions are associated with levels of annual risk of cancer death for a given level of lifetime exposure between 100 mrem/yr and 1 mrem/yr, upper and lower bounds, respectively. Concern is expressed with establishing public health standards at ALARA (as low as reasonably achievable) levels, which result in lower standards for reference, and views are presented on several issues of interest in regulations for protection of the public from radioactivity in drinking water. Based on the regulatory scheme suggested, the author concludes that existing standards for drinking water appear to be lower than necessary.     

Annual committed effective dose from olive oil (due to 238U, 232Th, and 222Rn) estimated for members of the Moroccan public from ingestion and skin application

Olive oil is traditionally refined and widely consumed by Moroccan rural populations. Uranium (238U), thorium (232Th), radon (222Rn), and thoron (220Rn) contents were measured in various locally produced olive oil samples collected in rural areas of Morocco. These radionuclides were also measured inside various bottled virgin olive oils consumed by the Moroccan populations. CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs) were used. Annual committed effective doses due to 238U, 232Th, and 222Rn from the ingestion of olive oil by the members of the general public were determined. The maximum total committed effective dose due to 238U, 232Th, and 222Rn from the ingestion of olive oil by adult members of Moroccan rural populations was found equal to 5.9 μSv y-1. The influence of pollution due to building material dusts and phosphates on the radiation dose to workers from the ingestion of olive oil was investigated, and it was found that the maximum total committed effective dose due to 238U, 232Th, and 222Rn was on the order of 0.22 mSy y-1. Committed effective doses to skin due to 238U, 232Th, and 222Rn from the application of olive oil masks by rural women were evaluated. The maximum total committed effective dose to skin due to 238U, 232Th, and 222Rn was found equal to 0.07 mSy y-1 cm-2.     

The assessment of human exposure to radionuclides from a uranium mill tailings release and mine dewatering effluent

This study provides an assessment of human exposure to radiation from a river system contaminated by radionuclides of the 238U decay series released through a dam break at a uranium mill tailings pond and by the continuous discharge of dewatering effluent from 2 uranium mines. The in vivo analyses of radionuclides in 6 Navajo Indians who lived near the river indicate no detectable elevations above background concentrations. Dose estimates for inhalation of suspended river sediment indicate a maximum annual 50-yr dose commitment of 204 mrem to the endosteum. Estimates of doses (50-yr dose commitments) from the ingestion of livestock range between 1 mrem (to liver) and 79 mrem (to bone) suggest that the major contribution to human exposure is from mine dewatering effluent that has been continuously released into the river system for many years. Although the estimated exposures do not exceed existing state or federal regulations, their magnitude justifies further measurement of radionuclides in animals and in the natural environment and the consideration of strategies to reduce radiation exposure to humans and animals.