Quality control of mitigation methods for unusually high indoor radon concentrations

The present study's objective was to control the quality of different mitigation methods for unusually high indoor radon (222Rn) concentrations of up to 274,000 Bq m(-3) in a village (Umhausen, 2,600 inhabitants) in western Tyrol, Austria. Five years after mitigation, five different remedial actions were examined on their quality by means of measuring indoor radon concentrations with charcoal liquid scintillation radon detectors and with a continuously recording AlphaGuard detector. Mitigation method in house 1--a mechanical intake and outlet ventilation system with heat exchanger in the basement, combined with a soil depressurization system--was characterized by long-term stability. With most favorable air pressure (+100 Pa) in the basement, mean basement radon concentrations in the winter were reduced from 200,000 Bq m(-3) to 3,000 Bq m(-3) by this method 5 y after mitigation. Acting against experts' instructions, the inhabitants had switched off the ventilation system most of the time to minimize power consumption although it had been proven that ventilation reduced mean basement radon concentration by a factor of about 3 in the winter and about 15 in the summer. Mitigation method in house 2-soil depressurization with two fans and loops of drainage tubes to withdraw radon from the region below the floor and outside the basement walls, and from soil below that part of the house with no basement-had been the most successful remedial measure until the winter of 1999 (i.e., 6 y after mitigation), when micro-cracks opened and consequently mean basement radon concentration increased from 250 Bq m(-3) to 1,500 Bq m(-3). Measures to block these microcracks and to minimize soil drying are being developed. Five years after mitigation, the remedial method used in house 3--a multilayer floor construction, where a fan was used to suck radon from a layer between bottom slab and floor-reduced winter mean radon concentration from 25,000 Bq m(-3) to 1,200 Bq m(-3), with the ventilation on and the basement door open. Mitigation method in house 4--a basement sealing technique--was unsuccessful with almost identical radon concentrations during all the five years since mitigation had started. Mitigation method in house 5--a waterproof basement technique especially for future homes--reduced mean basement radon concentration below 300 Bq m(-3) and mean ground floor radon concentration below 200 Bq m(-3), which is the Austrian action level for newly constructed buildings. These findings indicate that even in areas with extremely high radon concentrations, effective mitigation of indoor radon can be achieved provided that house-specific long-term, stable mitigation techniques are applied.     

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。     

Radon emanation in Saskatchewan soils

Saskatchewan prairie soils in central Canada were studied from areas where many homes are known to exceed the Health Canada indoor radon guideline of 200 Bq m. This study sampled 32 soils from 11 sites, which varied in clay content and presence of bedrock materials. Soils were analyzed for (238)U, (226)Ra, (222)Rn in soil gas, bulk density, moisture, and particle size. Radon emanation from the soil samples varied from 10% to 43% and increased significantly with clay content with radon concentrations in soil gas of 18-38 kBq m(-3). Total uranium in soils was 2.1-4 ppm and 26-51 Bq kg(-1) dry weight for (238)U, (234)Th, and (226)Ra. Homes built on soils with high clay content may be at greater risk of high radon levels, particularly when the soils are dry and cracked, enhancing their permeability to gases such as radon. One sample of coal bedrock, originating from Tertiary marine shales, was particularly high for total uranium (53 ppm), (238)U, (234)Th, and (226)Ra activities (68-1,303 Bq kg(-1)) with radon emanation up to 1,363 kBq m(-3).     

Nationwide survey of radon levels in Korea

A nationwide radon survey was conducted to provide data on the annual average indoor radon concentration in Korean homes. This survey also provided data on the variation of radon concentration with season, house type, and building age. The arithmetic mean (AM) of annual radon concentration in Korean homes was 53.4 +/- 57.5 Bq m(-3). The indoor radon concentration showed a lognormal distribution with a geometric mean (GM) and its standard deviation (GSD) of 43.3 +/- 1.8 Bq m(-3). The radon concentrations in the traditional Korean-style houses were about two times higher than those in apartments and row houses. The average annual outdoor radon concentration was 23.3 Bq m(-3). The average annual effective dose to the general public from radon was 1.63 mSv y(-1).     

Anomalously high radon concentrations in dwellings located on permeable glacial sediments.

Indoor radon concentrations were measured in different seasons in 104 dwellings located on a highly permeable ice-marginal moraine in Kinsarvik, Western Norway. The measurements revealed the highest indoor radon levels ever detected in Norway and extreme variations in seasonal and short-term indoor radon levels. Annual average indoor radon concentrations up to 56 000 Bq m(-3) and a mean value of 4340 Bq m(-3) for the whole residential area are reported. By using the ICRP conversion factors to effective dose, these indoor radon values correspond to a total annual effective dose of 930 mSv and 72 mSv, respectively. By using the conversion as recommended by UNSCEAR, the effective doses would be about 50% higher. The indoor radon concentrations are found to be strongly influenced by thermally induced flows of radon-bearing soil air directed towards the upper part of the ice-marginal deposit in winter and towards the area of lowest elevation in summer. The pattern of seasonal variations observed suggests that in areas where thermal convection may occur, annual average indoor radon levels should be derived from measurements performed both in summer and in winter.     

Indoor radon determination in dwellings located at Dikili geothermal area in Western Turkey

This paper presents the indoor radon concentrations in dwellings located in the Dikili geothermal area in western Turkey. Indoor radon monitoring was performed for 3 mo using 121 detectors installed in the living rooms and bedrooms of 62 houses selected from the region. A passive time-integrating radon measuring technique was applied by using CR-39 solid-state nuclear track detectors. Average indoor radon levels for the houses varied from 31 to 280 Bq m(-3). Corresponding annual effective doses were calculated, and risks for lung cancer due to inhalation of indoor radon were estimated.     

湛江市部分住房室内外空气中氡浓度测定

采用活性炭吸附闪烁法测定了湛江市部分住房室内、外空气中的平衡当量氡浓度。结果表明 ,住房室内、外空气中平衡当量氡浓度平均值分别为 2 5 2 7Bq/m3 和 14 6 8Bq/m3 ,室内空气中平衡当量氡浓度显著高于室外 (P <0 0 1) ;不同装饰材料的住房室内空气中平衡当量氡浓度各有差异 ,其中以花岗岩为装饰材料的住房室内平衡当量氡浓度 (31 18Bq/m3 )为最高 ,水泥地板住房 (14 71Bq/m3 )最低     

Seasonal variation in indoor radon concentrations in dwellings in six districts of the Punjab province, Pakistan

An indoor radon measurement survey has been carried out in six districts of the Punjab province. These included Gujranwala, Gujrat, Hafizabad, Sialkot, Narowal and Mandibahauddin districts. In each district, 40 representative houses were chosen and indoor radon levels were measured in these dwellings in autumn, winter, spring and summer seasons using CR-39 based NRPB radon dosimeters. After exposure to radon, the CR-39 detectors were etched in 25% NaOH at 80 degrees C and track densities were related to radon concentration levels. From the observed data, average radon concentration levels and a seasonal correction factor were calculated. The average 222Rn concentration level was found to vary from 40 +/- 15 to 160 +/- 32 Bq m(-3) and 38 +/- 17 to 141 +/- 26 Bq m(-3) in the bedrooms and living rooms of the houses surveyed, respectively. The annual mean effective dose received by the occupants has been calculated using ICRP (1993 Ann. ICRP 23) and UNSCEAR (2000 Sources and Effects of Ionizing Radiation (New York: United Nations)); it varied from 1.2 to 1.7 mSv and from 1.8 to 2.4 mSv, respectively.     

Assessment of natural radioactivity and radon exhalation rate in Sannur cave, eastern desert of Egypt.

Activity concentrations of 238U, 232Th and 40K in rocks and soil samples collected from Sannur cave, Beni Suef governorate, eastern desert of Egypt, were determined using the high-resolution gamma spectrometry technique. The results show that the concentrations of the naturally occurring radionuclides are the following: 238U ranged from 8.51 +/- 1.23 to 20.66 +/- 2.12 Bq kg(-1), 232Th ranged from 7.69 +/- 1.02 to 22.73 +/- 1.60 Bq kg(-1) and 40K ranged from 185.74 +/- 0.42 to 2084.70 +/- 23.30 Bq kg(-1). The radium equivalent activity (Raeq), the absorbed dose rate (D), and the external hazard index (Hex) were also calculated and compared to the international recommended values. The radon concentration and radon exhalation rate from the rock and soil samples were measured using the Can technique. The average value of annual effective dose for cave workers is 1.98 mSv y(-1), while for visitors it is 2.4 microSv per visit. The radon exhalation rate varies from 0.21 +/- 0.03 to 1.28 +/- 0.02 Bq m(-2) h(-1). A positive correlation has been observed between uranium content and radon exhalation rate.     

Chromosome aberrations study of pupils in high radon level elementary school

The ICRP Publication 65 recommends 200-600 Bq x m(-3) as the indoor radon action level for the general public. In Slovenia, a value of 400 Bq x m(-3) has been proposed but not yet approved. In a nation-wide radon project financed by the Health Inspectorate of Slovenia, it was discovered that the elementary school named "S3" belongs to a group of schools with elevated winter indoor radon concentrations up to 7,000 Bq x m(-3). Opening windows and doors during classes substantially decreased radon concentrations, but very seldom below 1,000 Bq x m(-3). Yearly effective doses for pupils, estimated according to ICRP 65, ranged from 7 to 11 mSv. Because the pupils have been subjected to the elevated radon concentrations, special preventive health checks have been performed. The examination protocol included mutagenetic tests, one for structural chromosomal aberrations and the other a micronucleus test. Altogether 85 pupils (37 girls and 48 boys) from the first four grades between the ages of 9 and 12 y were examined. An increase in cytogenetic damage was found for these pupils, compared to the control group, composed of pupils of the same age from another area with indoor radon concentrations in their school of below 400 Bq x m(-3). The incidence of structural chromosomal aberrations reached 2.0% (0.5-4) and micronucleus test was 6.52 per 500 cells with a maximum of 15 in some cases. In the control group structural chromosomal aberrations varied from 0.5 to 2.5%, while the maximum incidence of micronucleus was 9 micronucleus per 500 CB cells. The results obtained are preliminary and suggest a need to expand the study. A long-term radon survey, at least over a year, of the homes and wider residential environment of the pupils would be necessary to assess the correlation between radon exposure and both structural chromosomal aberrations and micronucleus findings.     

Radon concentrations in some dwellings of Tunisia

Indoor air radon concentrations are still unknown in Tunisia. For the first time, they have been determined in several regions of the country using open alpha track dosimeters containing LR-115 film. Measurements were taken in 69 dwellings located around greater Tunis during 1 y, changing dosimeters every 2 mo. In 12 other locations, devices were placed during 2 winter months. The median of 1,217 measurements was 40 Bq m(-3) and 93.4% of them were less than 100 Bq m(-3). The highest concentration was 392 Bq m(-3). In Tunis, concentrations were higher during winter. Indoor air radon figures varied with geographic location: the highest values were found in Jendouba, Gafsa, Beja, and Tataouine government districts where phosphate and lead mines and deposits are present. This first study showed that indoor air radon concentrations are low in Tunisia, but further studies should be performed in localized areas, taking into consideration the geology, the climatic variations, and the building material.     

Study of indoor radon levels in high-rise air-conditioned office buildings

A series of measurements were conducted to study the indoor radon pollution in air-conditioned high-rise office buildings. Continuous monitoring of indoor radon levels in nine air-conditioned premises located in six office buildings in Hong Kong was conducted from August 1996 to February 1998. Each of the tests lasted for at least 48 hours. The measurement covered both day time monitoring while the air-conditioning was on and night time monitoring while the air-conditioning was off. The indoor radon level followed inversely the operation pattern of the mechanical ventilation systems in the buildings. During office hours when the mechanical ventilation was on, the indoor radon level decayed and after the mechanical ventilation was off during non-office hours, the radon level increased. The average indoor radon level during office hours on the nine premises varied from 87 Bq/m3 to 296 Bq/m3, and the indoor averaged radon levels over both day time and night time periods without mechanical ventilation were about 25 percent higher. The air infiltration rate and the radon emission characteristics from the building materials were estimated from the radon build-up curves which were observed after the mechanical ventilation was off. The radon decay curve observed after the mechanical ventilation system was turned on was used to calculate the total fresh air intake rate. Average radon emanation rates of the building materials in the six buildings varied from 0.0019 to 0.0033 Bq/m2s. It has been found that building infiltration rate accounted for about 10-30 percent of the total building ventilation rate in the buildings depending on building tightness.     

Indoor radon in Kuwait

Indoor radon measurements were carried out in 300 dwellings in Kuwait using duplicate sets of charcoal detectors. Measurements were made at three different locations in the dwellings: living rooms, bedrooms, and basements. The results show that the radon concentration in the dwellings of Kuwait was found to vary in the range of 4.0-241.8 Bq m(-3) with a mean value of 32.8 Bq m(-3), and most values are confined within the range of 10-50 Bq m(-3) for all locations with few cases above the value of 100 Bq m(-3). Overall results show that the indoor radon concentration levels in Kuwait are relatively low, which is attributed to the use of air conditioning in summer and possible natural ventilation in winter. The radon concentration in basements was found to be relatively higher when compared to other rooms of the dwellings.     

Radon 222Rn in residential buildings of Swieradów Zdrój and Czerniawa Zdrój

Swieradrów Zdrój and Czerniawa Zdrój are located in Region Izera Block. A total of 789 radon passive dosimeters were distributed in 183 dwellings in these town Swieradów Zdrój and Czerniawa Zdrój to measure the indoor radon concentration in 1999. Three-five measurements were performed in each dwelling, one in the basement, and the others in the main bedroom, in the kitchen, in the bathroom, since these rooms are the most frequently occupied. In addition, the occupants of each dwelling were requested to answer a questionnaire in which a number of questions about the building, ventilation habits and other related aspects were formulated. A charcoal detectors (Pico-Rad system) were used in experiment. It is a passive short-term screening method of radon gas concentration measurements. The indoor radon level was found to range from 14.8 Bq/m3 to 5,723.9 Bq/m3. The arithmetic mean overall indoor concentration was 420.4 Bq/m3 and the geometric mean was 159.7 Bq/m3. The average concentration of indoor radon, which reflects the real risk for inhabitants, is 193.5 Bq/m3. The results hand a log-normal distribution. In Poland, an action level of 400 Bq/m3 was recommended for existing buildings and 200 Bq/m3 for newly built (after 1.01.1998) buildings. In about 23% rooms the level of Rn-222 were above the top limit of 400 Bq/m3. The highest average concentrations were present in a basement (mean 919.9 Bq/m3). A decrease of average activity were observed at the upper levels: at the ground floor (225.2 Bq/m3), at the first floor and at the higher floors (137.6 Bq/m3). The above results indicate that radon emission from the ground provides the main contribution to the radon concentration measured in dwellings indoors in Swieradów Zdrój and Czerniawa Zdrój. The effective dose to the population of the Swieradów Zdrój and Czerniawa Zdrój from indoor radon and its progeny can be derived from this data if we use an equilibrium factor of 0.4 between radon and its progeny and assuming an indoor occupation index of 0.8. Taking into account that a conversion coefficient of 1.1 mSv per mJ h m-3 is recommended in ICRP 65 for members of public, the measured average annual dose is then about 3.3 mSv per year.     

The measurement of radon working levels at a mineral separation pilot plant in Cox''s Bazar,Bangladesh

Beach Sand Exploitation Centre at Cox's Bazar, Bangladesh, produces commercial grade concentrations of magnetite, ilmenite, zircon, etc., from the high-grade accumulations available along the beach and foredune of Cox's Bazar. Solid state nuclear track detectors (CR-39 foils) were used to determine indoor radon concentration of radioactive mineral sands and the technologically enhanced radiation level inside the pilot plant of the Centre. It is found that the concentrations at processed mineral stock areas are high, and the maximum concentration was found to be 2,103 +/- 331 Bq m(-3) (0.23 +/- 0.03 WL). The indoor concentration of radon and its decay products in the raw sand stock area and at other locations was in the range of 116 +/- 27 Bq m(-3) (0.03 +/- 0.003 WL) to 2,042 +/- 233 Bq m(-3) (0.22 +/- 0.03 WL).     

Survey of indoor radon concentrations in Fukuoka and Kagoshima prefectures

It is now well established that radon and its daughter products account for nearly half of the average population exposure to ionizing radiations and that radon is the greatest single source of natural radiation to the population. Radon and its daughters are alpha-emitters, which are more biologically damaging than beta- and gamma-radiations. A nationwide survey of radon concentration was conducted by the National Institute of Radiological Sciences in order to estimate the contribution of radon and its daughters to the population dose in Japan. Authors surveyed indoor radon concentrations in Fukuoka and Kagoshima prefectures as part of this project. A passive type radon dosimeter, in which a sheet of polycarbonate film as the alpha-ray detector was mounted, was used to measure indoor radon concentrations. The resulting distribution of the average annual indoor radon concentrations in both prefectures can be characterized by an arithmetic mean of 24.4 Bq/m3 and a standard deviation of 13.1 Bq/m3, by a geometric mean of 22.2 Bq/m3, and by a median of 20.7 Bq/m3. The geometric means of the distributions for Fukuoka and Kagoshima were 25.4, and 18.4 Bq/m3, respectively. Radon concentrations were also generally high in winter and low in summer. Regarding the analysis of correlations between the concentrations and construction materials, radon concentrations were generally high in Japanese houses with earthen walls and in concrete structures. These results showed that seasons, the type of building materials, and regional differences were significant factors in the variation of indoor radon concentration.     

Radon in Tunisian buildings

Radon is a natural radioactive gas produced by decay of uranium and radium present in soils. Diluted in air, in confined atmospheres, it may accumulate in high concentrations. Inhalation of radon and its progeny is thought to increase lung cancer risk. For the first time, air radon concentrations were determined in 1151 dwellings situated in all the inhabited regions of Tunisia, using open alpha-track dosimeters exposed during two months. The median of 1864 measurements was 36 Bq m(-3) (with a maximum of 512 Bq m(-3), most of them being less than 100 Bq m(-3). All results were under the International Instances recommended range.     

Radon action level for high-rise buildings

Radon and its progeny are the major contributors to the natural radiation dose received by human beings. Many countries and radiological authorities have recommended radon action levels to limit the indoor radon concentrations and, hence, the annual doses to the general public. Since the sources of indoor radon and the methods for reducing its concentration are different for different types of buildings, social and economic factors have to be considered when setting the action level. But so far no action levels are specifically recommended for cities that have dwellings and offices all housed in high-rise buildings. In this study, an optimization approach was used to determine an action level for high-rise buildings based on data obtained through previous territory-wide radon surveys. A protection cost of HK$0.044 per unit fresh air change rate per unit volume and a detriment cost of HK$120,000 per person-Sv were used, which gave a minimum total cost at an action level of 200 Bq m(-3). The optimization analyses were repeated for different simulated radon distributions and living environment, which resulted in quite significantly different action levels. Finally, an action level of 200 Bq m(-3) was recommended for existing buildings and 150 Bq m(-3) for newly built buildings.     

地热田高氡建筑治理与效果评价

目的 探讨地热田高氡房屋氡的来源与治理.方法 α径迹探测器(ATD)分冬夏两个季节测量室内和土壤中的氡浓度.采用γ能谱法测量房屋主体建材放射性核素含量;采用6150 AD/6HX-γ剂量率仪测量房屋主体建材的外照射剂量率;对其中一栋房屋实施土壤减压技术的降氡改造.结果 夏冬季32个房间氡浓度均值分别为(106.4±63...     

A nation-wide survey on indoor radon from 2007 to 2010 in Japan

In two previous nation-wide surveys in the late 1980s and early 1990s, Japanese indoor radon concentrations increased in homes built after the mid 1970s. In order to ascertain whether this trend continued, a nation-wide survey was conducted from 2007 to 2010. In total 3,900 houses were allocated to 47 prefectures by the Neyman allocation method and 3,461 radon measurements were performed (88.7% success). The fraction of reinforced concrete / concrete block buildings was 32.4%, similar to the value from national statistics. Arithmetic mean (standard deviation, SD) and geometric mean (geometric SD) of radon concentration after adjusting for seasonal fluctuation were 14.3 (14.7) and 10.8 (2.1) Bq/m(3). The corresponding population-weighted values were 13.7 (12.3) and 10.4 (2.0) Bq/m(3), respectively. It was estimated that only 0.1% of dwellings exceed 100 Bq/m(3), a new WHO reference level for indoor radon. Radon concentrations were highest in houses constructed in the mid 1980s and decreased thereafter. In conclusion, arithmetic mean indoor radon in the present survey was slightly lower than in previous surveys and significant reductions in indoor radon concentrations in both wooden and concrete houses can be attributed to alterations in Japanese housing styles in recent decades.