Swedish limitation schemes to decrease Rn daughters in indoor air

The limitation schemes to decrease Rn daughter concentrations in Swedish homes are described. The application of the Swedish provisional limitation scheme in use since 1980 is also reported and compared with international and national recommendations in other countries.     

Dependence of electrostatic diffusion of Rn progeny on environmental parameters

In previous work it was established that electrostatic diffusion of Rn progeny attached to aerosols can be used for passive dosimetry by replacing the pump-filter assembly in an active dosimeter by an electret. In the present work, results are presented on the dependence of activity collected by an electret on aerosol concentration, aerosol diameter, attachment rate of Rn progeny to aerosols, unattached fraction of Rn progeny, and Rn progeny concentrations. The electrostatic flow rate of Rn progeny is defined and all relationships analyzed in terms of this flow rate. The electrostatic flow rate is found to be reasonably constant for 0.03 micron less than particle diameter less than 0.09 micron, unattached fraction of 218Po less than 0.40 and 70,000/cm3 less than aerosol concentration less than 180,000/cm3; experimentally obtained data outside these limits are too few to draw any definite conclusions. The results are useful from a practical point of view because typical U mine conditions are described by these limits.     

Health effects and risks from 222Rn in drinking water

This paper presents an evaluation of the inhalation and ingestion doses from exposure to Rn and Rn progeny; an overview of the human and animal health-effects data; estimations of the cancer risks from Rn and Rn-progeny exposures; and suggested limits for Rn concentrations in drinking water and indoor air. We suggest that a rounded Rn-in-water concentration limit of 10,000 pCi/l can be supported by health-effects considerations alone, based on the conservative "tolerance dose" concept and other conservative assumptions regarding lung dose. A practical concentration limit (or action level) of 20,000 pCi/l has been derived by estimations of exposure distributions in the United States and in relation to current U.S. Environmental Protection Agency (EPA) standards for U-tailings-contaminated buildings. Research needed for resolution of the uncertainties in these estimates is suggested. We conclude that before a maximum contaminant level (MCL) for Rn in water can be firmly established, the broader issue of setting the MCL for Rn in indoor air must be addressed.     

Indoor 222Rn measurements in Sweden with the solid-state nuclear track detector technique

Measurements of the indoor radon and radon daughter concentrations were performed in several thousand Swedish houses during the years 1979-1984 with the solid state nuclear track detector technique (SSNTD technique). The investigation focused on structures containing building materials of light-weight concrete with enhanced amounts of U. The detectors used nuclear track films exposed for 1 mo. The film basically measures total airborne alpha activity but may be calibrated in units of EER in an environment with known 222Rn and daughter concentrations. (EER is here the equilibrium equivalent concentration of Rn with the equilibrium factor F = 0.5.) The investigation was performed in various municipalities in collaboration with the local public health and environmental authorities. The investigation included 6700 individual measurements in detached (single-family) houses as well as in apartment houses. A small percentage of the dwellings exhibited Rn daughter concentrations (EER) exceeding 400 Bq m-3. It was found in detached houses that the concentrations were higher in the basement floor than in the entrance floor of a house. The Rn daughter values in the bedrooms were similar to values in any other room (mainly on the same floor) of the structure. The Rn daughter levels in apartment houses were lower than in single-family houses. The seasonal variations of the Rn daughter levels are presented and show that the levels in summertime are approximately equal to the levels in the winter.     

Validation of a geologically based radon risk map: are the indoor radon concentrations higher in high-risk areas?

Since geographically coded information is frequently used in studies of the relationships between environmental factors and illness at the population level and by authorities for promotion of mitigation, knowledge about the validity of proxy measures is essential. This study was an evaluation of a geologically based map describing the risk for high radon levels, which was used by the municipal authorities to determine the necessity of remedial actions. Annual mean radon gas concentrations for a random sample of one-family homes selected from high-risk areas (n = 252) were compared with those of a random sample of homes from normal and low-risk areas (n = 259). No difference in geometric mean radon concentration was found between the areas, 101 Bq m(-3) and 103 Bq m(-3), respectively. The proportion of homes in each area with radon gas concentrations above the current Swedish administrative limit value for mitigation (400 Bq m(-3)) was similar, approximately 10%. We conclude that the radon risk map was unsuitable for identifying areas of concern. The findings also indicate that geologically based and geographically coded information as a proxy for human exposures can be safely used for scientific and administrative purposes only following validation.     

Levels of provision and of dependency in residential homes for the elderly: implications for planning

Two surveys of dependency among elderly residents in local authority homes are reported. Dependency levels are compared in the light of the large difference in the amount of accommodation provided by the two authorities. Dependency levels are shown to be unrelated to level of provision. The authors suggest that this finding contradicts assumptions frequently made in planning institutional provision for the elderly. Reducing the number of places in residential care, providing specialist homes or establishing nursing homes may not therefore have the intended effect of changing the dependency mix in institutional care.     

Regulatory control of indoor Rn

Regulation of indoor Rn is explored in the context of cost-effectiveness of regulatory action. Evaluation of cost (i.e., mitigation expenses) and benefits (i.e., savings associated with medical expenses and lost productivity related to lung cancer) at various action levels indicate that regulatory programs would be economically inefficient and unreasonable if standards were established at or below the current EPA action guide (150 Bq m-3 or less). For the approximately 95% of U.S. homes with Rn levels near or below 150 Bq m-3, government programs should continue to focus on public information and consumer protection. For the small number of homes with high Rn levels, government programs should focus on identifying high risk homes and encouraging homeowners to reduce Rn levels. Because of the potential for substantial risk reduction, such efforts would be cost-effective in these homes.     

Indoor Rn levels in different geological areas in Switzerland

The distribution of indoor Rn concentrations in different geological areas in Switzerland was studied using passive alpha-track detectors. Measurements involving a sample of 400 single-family homes were made in the cellar, on the ground floor and the first floor, respectively. On the basis of a pilot survey, the country was divided into four zones in which the Rn distribution in houses was analyzed separately. The indoor exposure to Rn and Rn decay products is quite variable from region to region. The geology of the different areas was found to be an important factor in determining the mean value Rn levels. In the basin north of the Alps, where the population centers are located, a median Rn gas level of 47 Bq m-3 for the living area was found. The arithmetic mean value of 60 Bq m-3 in this region leads to an annual effective dose equivalent of about 1.8 mSv. For the population living in alpine areas, an arithmetic mean value exceeding 200 Bq m-3 will lead to an annual effective dose equivalent in the range of 6 mSv. The estimated exposure to Rn and Rn decay products for the upper one-percentile of the homes in the most affected alpine region even exceeds the annual limit of 50 mSv effective dose equivalent for occupational exposure.     

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   

Summertime elevation of 222Rn levels in Huntsville, Alabama

Indoor Rn concentrations and Rn in adjacent karst terrains were studied at four houses with crawlspaces in Huntsville, AL. In warm summertime weather, Rn-rich air may vent through limestone solution cavities exposed as holes at the surface of the properties. A probable interrelated-finding is that the indoor levels of 222Rn are distinctly higher in the summer than winter. The karst underlying the homes is structurally faulted and, in all probability, facilitates Rn transport from the solution cavities to the crawlspaces. Abrupt day-to-day changes in indoor Rn concentrations were recorded in addition to large seasonal changes. If the owners or residents of these particular homes had attempted to make, and interpret, short-term screening measurements for Rn during the fall season, problems, including false negatives, could have arisen because of order-of-magnitude changes in Rn concentration occurring over a few days. The best time of year to make screening measurements would be during the summer when indoor Rn concentrations are more likely to reach their maximum values.     

Correlation among the terrestrial gamma radiation, the indoor air 222Rn, and the tap water 222Rn in Switzerland

The external gamma radiation and the indoor air Rn (222Rn) concentration were measured in 55 houses of the South East Grisons, the Urseren valley, and the Upper Rhine valley (crystalline subsoils) and in 39 houses of the Molasse basin and the Helvetic nappes (sedimentary subsoils). In homes located on a crystalline subsoil, a mean cellar gamma level of 1.40 mGy y-1 was measured, which is twice the mean gamma level of 0.70 mGy y-1 found in homes built on a sedimentary subsoil. The cellar 222Rn gas concentration is about six times higher in houses with a crystalline subsoil (1232 Bq m-3) than in houses with a sedimentary subsoil (201 Bq m-3). Although a weak correlation is observed between the mean gamma radiation levels and mean cellar 222Rn gas concentrations for the five subregions investigated, the gamma levels and the 222Rn gas concentrations do not correlate for single homes. For the population living on the ground floor of a house with a crystalline subsoil, the gamma radiation and the indoor air 222Rn lead to estimated mean exposures of 1.16 mSv and 9.44 mSv effective dose equivalent per year, respectively. In houses with a sedimentary subsoil, these mean exposures lead to 0.68 mSv y-1 and 3.22 mSv y-1, respectively. A mean tap water 222Rn content of 38.3 Bq L-1 and 10.4 Bq L-1 was measured in 31 villages with a crystalline subsoil and 73 villages with a sedimentary subsoil, respectively. Radon-222 degasing from the tap water into the indoor air leads to an additional exposure of about 0.11 mSv y-1 and 0.03 mSv y-1 in homes with a crystalline subsoil and homes with a sedimentary subsoil, respectively.     

A simple two-count method for routine monitoring of 222Rn and 220Rn progeny working levels in U mines

In the case of U mines containing Th, the total alpha energy will contain contributions from both 222Rn progeny and 220Rn progeny. A simple routine grab sampling monitoring scheme is therefore needed for separate measurement of the working levels of 222Rn and 220Rn progeny. The scheme presented here is based on a short delay period after sampling (2 min) for 222Rn progeny and a long delay period (340 min) before counting 220Rn progeny. An advantage of this scheme is that no corrections need to be made to the 222Rn progeny working level for the presence of 220Rn progeny. Such corrections must be made in the commonly used Kusnetz scheme.     

An instrument for measuring equilibrium-equivalent 222Rn and 220Rn concentrations with etched track detectors.

To simultaneously measure both 222Rn and 220Rn progeny concentrations, a new type of portable integrating monitor with allyl diglycol carbonate (CR-39) plastic detectors was developed. The monitor gives the average equilibrium-equivalent 222Rn and 220Rn concentrations (EEC(RN) and EEC(Tn)) during sampling intervals. The detection efficiencies of the alpha particles were calculated by Monte Carlo method. The lower limits of detection for EEC(Rn) and EEC(Tn) are estimated to be 0.57 Bq m(-3) and 0.07 Bq m(-3) for 24 h continuously sampling at a flow rate of 0.8 L min(-1). The measuring results with the new type monitors were confirmed through intercomparison experiments. In a small survey, a rather high 220Rn progeny concentration with an average of 1.73 Bq m(-3) was observed in traditional Japanese dwellings with soil/mud plastered walls. On the other hand, a very high 232Th concentration in soil was reported in China. They suggested that there is a possibility of high 220Rn progeny concentration in both Japan and China.     

Radon-222, 222Rn progeny, and 220Rn progeny levels in 70 houses

A year-long, multipollutant, indoor air quality study involving 70 occupied houses in four states was completed in 1987. All of the houses included in the study had a partial or complete basement with a concrete slab floor and block walls. On an approximately quarterly schedule, integrating monitors for short-lived Rn progeny, nitrogen dioxide, formaldehyde, and water vapor were exposed for 1 wk in each house on both the basement and main floors. At the beginning of the study, a pair of alpha-track detectors were placed on top of the refrigerator in the kitchen (or some other sampling location on the main floor) and at a location in the basement. One detector at each location was left in place for a year while the other detector was retrieved and replaced once every 3-mo period. In addition, short-term measurements of Rn and 222Rn progeny were made at all sampling locations once per quarter. In this study, comparisons were made between: (1) seasonal and annual averages, (2) summer and winter averages, (3) living-area and basement results, (4) 222Rn and 220Rn progeny, and (5) short- and long-term measurements. The Rn and Rn progeny concentrations in houses near Huntsville, AL were found to be well above recommended action levels (150 Bq m-3). For houses near Birmingham, AL, summer Rn concentrations were found to exceed winter concentrations, whereas for the other houses in the study, winter concentrations exceeded summer concentrations. Potential alpha energy concentrations (PAEC) from 220Rn progeny were found to be generally less than PAEC from 222Rn.     

Radon concentrations inside public and commercial buildings in the Pittsburgh area

Radon concentrations in ambient air from numerous schools, stores and other public and commercial buildings in the Pittsburgh, PA, area were measured by grab sampling. This is more appropriate than using long-term integrating monitors because of the correlation between times of occupancy and Rn levels. Results indicate that Rn concentrations in these buildings are nearly an order of magnitude less than in homes, and not much higher than outdoors. Variations among sites is also much less than for homes, probably because there is less variability in ventilation and building maintenance practices. Colleges and universities have somewhat higher Rn levels and a larger degree of variability than commercial buildings or hospitals. There was no indication of higher Rn levels in cold weather than in warm weather, or of correlations with the age of the building.     

Progeny enhanced deposition rates primarily from increased particle diffusivity at high radon concentrations

Prior work found that high 222Rn concentrations produced an enhanced radon progeny surface deposition effect (EDE) in a 0.283-m3 electrically grounded aluminum test chamber. To study a possible charge mobility effect, we report here additional measurements with the chamber lined with nonconducting, insulated materials. Specifically, with insulated, chemically clean glass we provide results of measurements at a number of 222Rn concentrations past the threshold and transition 222Rn levels (up to 60 kBq m(-3)). For EDE it was found at most a 14% charge mobility deposition effect. Without electrical grounding in the Al chamber with +/- 2,000 DC volts applied showed a 10% increase in 218Po surface deposition. Ambient and hot (37 degrees C) wetted filter paper to simulate lung tissue was measured and showed EDE of the same factor of > or = 2 as for all other materials. It is concluded that the enhanced progeny deposition from high radon concentration is primarily from a decrease in attached fraction, thus reducing progeny mean particle size, and increasing diffusivity and surface deposition.     

Estimating Rn-induced lung cancer in the United States

The proportion of lung cancer deaths attributable to Rn among residents of single-family homes in the U.S. (approximately 70% of the housing stock) is estimated using the log-normal distribution of Rn concentrations proposed by Nero et al. (1986) and the risk model developed by the National Academy of Sciences' BEIR IV Committee. The risk model, together with the exposure distribution, predicts that approximately 14% of lung cancer deaths among such residents (about 13,300 deaths per year, or 10% of all U.S. lung cancer deaths) may be due to indoor Rn exposure. The 95% confidence interval is 7%-25%, or approximately 6600 to 24,000 lung cancer deaths. These estimated attributable risks due to Rn are similar for males and females and for smokers and nonsmokers, but higher baseline risks of lung cancer result in much larger absolute numbers of Rn-attributable cancers among males (approximately 9000) and among smokers (approximately 11,000). Because of the apparent skewness of the exposure distribution, most of the contribution to the attributable risks arises from exposure rates below 148 Bq m-3 (4 pCi L-1), i.e., below the EPA "action level." As a result, if all exposure rates that exceed 148 Bq m-3 (approximately 8% of homes) were eliminated, the models predict that the total annual lung cancer burden in the U.S. would drop by 4-5%, or by about 3800 lung cancer deaths, in contrast to a maximum reduction of 14% if all indoor Rn exposure above the 1st percentile were eliminated.     

Assessing future trends in indoor air quality

Several national and international health organizations have derived concentration levels below which adverse effects on men are not expected or levels below which the excess risk for individuals is less than a specified value. For every priority pollutant indoor concentrations below this limit are considered "healthy." The percentage of Dutch homes exceeding such a limit is taken as a measure of indoor air quality for that component. The present and future indoor air quality of the Dutch housing stock is described for fourteen air pollutants. The highest percentages are scored by radon, environmental tobacco smoke, nitrogen dioxide from unvented combustion, and the potential presence of housedust mite and mould allergen in damp houses. Although the trend for all priority pollutants is downward the most serious ones remain high in the coming decades if no additional measures will be instituted.     

Influence of subsoil geology and construction technique on indoor air 222Rn levels in 80 houses of the central Swiss Alps

The indoor 222Rn level depends mainly on the subsoil geology, the cellar floor permeability, the cellar aeration, the air-tightness of the homes, and the aeration habits of the occupants. These five parameters and the 222Rn levels in the cellar and in the living room on the ground floor were compiled in 80 one- or two-family houses of the central Swiss Alps. The 222Rn levels were measured with passive alpha track detectors. Houses located on a granite, ortho-gneiss or verrucano subsoil have a cellar 222Rn level that is on the average 4.4 times higher than houses which are built on grey-schist or sediments. The cellar level is on the average 5.4 times higher if the cellar has partially a gravel or earth floor than if the whole cellar surface is covered with a concrete floor. Energy-efficient, highly air-tightened homes have a living room level that is on the average 1.8 times higher than normally insulated conventional homes. In the cellars and the living rooms of the 80 houses considered, arithmetic mean 222Rn levels of 724 Bq m-3 (20 pCi L-1) and 178 Bq m-3 (4.8 pCi L-1), respectively, were found. In the central Swiss Alps 222Rn and 222Rn decay products lead to an estimated mean exposure of 5.3 mSv effective dose equivalent per year.     

崇明县空气中氡浓度水平调查与评价

目的 了解崇明县室内外氡浓度水平并估算其所致公众的受照剂量。方法 根据2010年全国人口普查崇明县乡镇人口比例、房屋建筑类型、建筑年代和主体建筑材料等对测量样本进行分类选择。使用美国Durridge公司制造RAD7型电子氡气检测仪对室内外氡进行测量,数据采用SPSS 17.0软件进行统计分析。结果 本次调查的室内²²²Rn浓度范围为5.75~195.29 Bq/m³,平均浓度为(25.76±2.07) Bq/m³。约有73.89%的房屋内氡浓度低于40 Bq/m³。室外²²²Rn浓度的范围为5.70~19.32 Bq/m³,平均浓度为(9.92±1.43) Bq/m³。结论 本次调查的崇明县室内氡浓度均未超过国家推荐的控制限值。崇明县居民吸入氡所致人年均有效剂量为0.74 mSv。