Modeling seasonal variation in indoor radon concentrations

Radon, a well-established risk factor for human lung cancer, is present at low concentrations in most homes. Consequently, many countries have established national guidelines for residential radon concentrations. In this article, we evaluate two models for describing seasonal variation in residential radon concentrations based on the data from a large case-control study conducted in Winnipeg, Canada. In this study, radon levels in homes were monitored during two successive 6-month periods, with integrated annual radon concentrations obtained using CR-39 alpha-track detectors. Significant differences were noted among measurements taken during different seasons of the year. Using the model introduced by Pinel et al. (1995) to describe temporal variation in residential radon levels in southwest England using seasonal adjustment factors, reasonable predictions of annual average radon concentrations were obtained from the 6-month integrated radon measurements. However, a simple multiplicative model was found to provide better predictions than the seasonal adjustment model. Although model coefficients vary somewhat from one geographic location to another, the concordance with respect discriminating between results above and below 150 Bq/m(3) in Winnipeg was in the range 85-90% using seasonal adjustment models with coefficients derived from data in either Winnipeg or southwest England.     

西藏居室内氡浓度调查及所致居民剂量估算

目的 在国内城市室内氡呈上升趋势的背景下,为了获取现阶段西藏地区室内氡浓度水平,开展本次西藏地区室内氡浓度调查工作。方法 采用KF606B型固体核径迹氡累积探测器,对西藏自治区居室氡浓度进行测量,测量周期6～12个月。结果 西藏地区138间居室内氡浓度范围为14～119 Bq·m^-3,均值为（47.8 ±23.0） Bq·m^-3。氡浓度大于100 Bq·m^-3房间有5个,占总调查房间数的4%。居室内氡所致西藏地区居民有效剂量范围为0.46～3.89 mSv·a^-1,均值为1.56 mSv·a^-1。文章还对不同调查地区、城镇/农村、不同建筑类型和不同建筑年代居室内氡浓度进行了比较分析。结论 本次居室内氡浓度调查结果比上世纪八九十年代西藏地区测量结果有显著增高。     

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.     

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.     

个旧市郊室内氡、钍射气浓度和地面γ辐射水平初步调查

目的调查个旧地区居室内氡（^222Rn）、钍射气（^220Rn）及其子体水平，明确钍射气的剂量贡献。方法考虑住宅类型和地理分布因素，从个旧市郊某村选取建筑结构有代表性的50户住宅的主卧室，采用氡-钍射气鉴别探测器测量氡、钍射气浓度，用沉积率装置测量钍射气子体浓度。其中14间居室采用连续性氡测量探测器和α谱氡、钍射气鉴别探测器测量氡、钍射气浓度，空气采样滤膜结合CR-39探测器测量钍射气衰变产物浓度，碘化钠闪烁计数器测量地表γ剂量率。结果50间居室的氡浓度为32～498Bq／m^3，平均136Bq／m^3；钍射气浓度为39～7908Bq／m^3，平均3297Bq／m^3；钍射气子体浓度为2．0～23．9Bq／m^3，平均10．2Bq／m^3。钍射气子体衰变产物致居民年平均有效剂量大于氡子体衰变产物的平均年有效剂量（2．9mSv vs 1．6mSv）。结论个旧市郊部分居室室内钍射气及其子体浓度高，钍射气子体的剂量贡献要高于氡子体的剂量贡献。在个旧开展氡致肺癌危险评价研究应当考虑钍射气子体的剂量贡献。     

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.     

Spatial and temporal indoor radon variations.

This paper examines the ability of standard radon measurement protocols to predict long-term radon concentrations in houses located in the upper Midwest. It was observed that: (1) significant radon variations can occur on a spatial scale as small as a single floor; (2) radon measurements that integrate for periods less than 3 mo are reliable only to within a factor of 2 or more; and (3) contemporary, short-term measurements within existing structures may not accurately reflect past radon concentrations. Two-hundred forty-three occupied houses located in 40 towns were monitored for at least 1 y using alpha-track detectors. If lifetime radon exposure estimates need to be determined accurately, then long-term, integrating radon detectors should be placed in several rooms of each house. In radon atmospheres that may not be stable for long periods of time, it is suggested that multiple, year-long measurements or surface alpha activity measurements in combination with year-long alpha-track measurements are needed for an accurate lifetime radon assessment.     

Systematic indoor radon and gamma-ray measurements in Slovenian schools

During the winter months of 1992/93 and 1993/94, instantaneous indoor radon concentrations and gamma dose rates were measured in 890 schools in Slovenia attended in total by about 280,000 pupils. Under "closed conditions," the room to be surveyed was closed for more than 12 h prior to sampling, the air was sampled into alpha scintillation cells with a volume of 700 cm3, and alpha activity was measured. An arithmetic mean of 168 Bq m(-3) and a geometric mean of 82 Bq m(-3) were obtained. In 67% of schools, indoor radon concentrations were below 100 Bq m(-3), and in 8.7% (77 schools with about 16,000 pupils) they exceeded 400 Bq m(-3), which is the proposed Slovene action level. In the majority of cases, radon concentrations were high due to the geological characteristics of the ground. Approximately 70% of schools with high radon levels were found in the Karst region. Gamma dose rates were measured using a portable scintillation counter. An arithmetic mean of 102 nGy h(-1) and a geometric mean of 95 nGy h(-1) were obtained. No extraordinarily high values were recorded.     

室内空气中氡污染防治的研究进展

随着居民生活水平的不断提高,人们环保意识的加强,室内空气中氡的对人体健康的影响已成为人们关注的热点。作者介绍了近几年国内居室内空气中氡气的主要污染来源和状况、阐述了氡对人体健康的危害;并针对室内氡污染的来源,本文总结了国家制定的相应标准和规范,提出了有效、具体的防氡污染措施和治理方法;以达到创造健康室内环境的目的。     

Long term measurements of indoor radon equilibrium factor

To provide detailed information for bronchial dose estimates, aerosol particle size distributions, and radon gas concentration, measurements were made in six residential homes and three laboratory rooms in different office buildings in the city of Ottawa. In the literature, most particle size distribution measurements are taken with samplers operating for a few days at most. In this study, the particle size samplers collected the samples from 77 to 162 d. The equilibrium factor determined from the long-term measurements ranged from 0.6 to almost 1 with an average of 0.75. Even though radon concentrations were quite different between residential setting and office buildings, the average equilibrium factor was similar in the two different indoor environments. The results suggest that at least in some basements, if they were occupied, the radon dose would be about twice as high as normally estimated from the conventional F(eq) value of 0.4.     

降氡方法在室内氡污染治理中的应用与分析

目的 探索降低住宅氡及其子体浓度水平的合适方法.方法 选取3个房间分别采取自然通风、空气净化器、密封屏蔽的措施后,使用EQF3120型氡及其子体测量仪测量室内氡及其子体浓度,α核径迹探测器测量室内氡浓度,并比较不同方法的降氡效果.结果 自然通风2～10 h后,房间内氡、结合态氡子体和未结合态氡子体浓度平均降低率分别为8...     

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.     

Cost evaluation of control measures for indoor radon progeny

Based on assumed conditions within a typical U.S. home, annualized costs for reducing indoor airborne radon progeny concentrations have been calculated for a variety of methods of control. These analyses were limited to methods for control in existing homes. Control through modified construction techniques was not evaluated. Methods assessed included increased air circulation, increased ventilation, particle removal using electrostatic precipitation and unipolar ion generation, and the application of sealants to room surfaces. Although surface sealants proved to be reasonably cost-effective per person- sievert dose reduction, such sealants are prone to cracking and the durability of their effectiveness is questionable. Use of ceiling fans for increased air circulation and particle deposition appears to be least cost-effective, but this method may be attractive in some cases for reasons of comfort. The use of unipolar ion generators appears to be the best approach from the standpoint of cost effectiveness. These devices are also easy to install and are esthetically readily acceptable.     

Models for retrospective quantification of indoor radon exposure in case-control studies

In epidemiologic studies on lung cancer risk due to indoor radon the quantification of individual radon exposure over a long time period is one of the main issues. Therefore, radon measurements in one or more dwellings, which in total have been inhabited by the participants for a sufficient time-period, are necessary as well as consideration of changes of building characteristics and ventilation habits, which influence radon concentration. Given data on 1-y alpha-track measurements and personal information from 6,000 participants of case-control studies in West and East Germany, an improved method is developed to assess individual radon exposure histories. Times spent in different rooms of the dwelling, which are known from a personal questionnaire, are taken into account. The time spent outside the house (average fraction 45%) varies substantially among the participants. Therefore, assuming a substantially lower radon exposure outside the dwelling, the residence time constitutes an important aspect of total radon exposure. By means of an analysis of variance, important determinants of indoor radon are identified, namely constant conditions such as type of house (one family house or multiple dwelling), type of construction (half-timbered, massive construction, lightweight construction), year of construction, floor and type of basement, and changeable conditions such as heating system, window insulation, and airing habits. A correction of measurements in former dwellings by factors derived from the analysis is applied if current living conditions differ from those of the participants at the time when they were living in the particular dwellings. In rare cases the adjustment for changes leads to a correction of the measurements with a factor of about 1.4, but a reduction of 5% on average only. Exposure assessment can be improved by considering time at home and changes of building and ventilation conditions that affect radon concentration. The major concern that changes in ventilation habits and building conditions lead to substantial errors in exposure (and therefore risk) assessment cannot be confirmed in the data analyzed.     

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.     

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