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PubMed1992

Lung cancers associated with thorotrast exposure: high incidence of small-cell carcinoma and implications for estimation of radon risk.

The widely accepted concept that the alpha-emitting radionuclide radon (222Rn, 220Rn) induces lung cancers in humans has been based on the excess of lung tumours observed in underground miners extracting uranium or other substances. However, this poses the important question of whether radon is the only carcinogenic factor because such miners are also heavily exposed to mine dusts including silicates, diesel exhaust, etc. in their working environment. Patients to whom Thorotrast was administered continuously exhale radon (220Rn) derived from 232Th deposits in the body and therefore provide a good model for lung carcinogenesis by radon without concomitant dust exposure. We therefore investigated lung-cancer incidence in our epidemiological follow-up series, analysing the histological types of 11 lung cancers which were found among 359 Thorotrast autopsy cases and measuring radioactivity in the breath of living Thorotrast patients. The study revealed that, while the proportion of small-cell lung cancers considered to be related to alpha-particles was significantly increased, the overall lung cancer incidence was not significantly higher than in controls, in spite of the high level of 220Rn in the patients' breath. This result suggests that radon in the lung does induce cancers (particularly small-cell carcinomas) but that the induction rate is not as high as expected from risk factors associated with mining. Thus, excess lung cancers among the miners might be related to the combined effects of exposure to radon and mine dusts, and not solely to radon.

Aged↗
PubMed1990

Indoor air radon.

This review concerns primarily the health effects that result from indoor air exposure to radon gas and its progeny. Radon enters homes mainly from the soil through cracks in the foundation and other holes to the geologic deposits beneath these structures. Once inside the home the gas decays (half-life 3.8 d) and the ionized atoms adsorb to dust particles and are inhaled. These particles lodge in the lung and can cause lung cancer. The introduction to this review gives some background properties of radon and its progeny that are important to understanding this public health problem as well as a discussion of the units used to describe its concentrations. The data describing the health effects of inhaled radon and its progeny come both from epidemiological and animal studies. The estimates of risk from these two data bases are consistent within a factor of two. The epidemiological studies are primarily for hard rock miners, although some data exist for environmental exposures. The most complete studies are those of the US, Canadian, and Czechoslovakian uranium miners. Although all studies have some deficiencies, those of major importance include uranium miners in Saskatchewan, Canada, Swedish iron miners, and Newfoundland fluorspar miners. These six studies provide varying degrees of detail in the form of dose-response curves. Other epidemiological studies that do not provide quantitative dose-response information, but are useful in describing the health effects, include coal, iron ore and tin miners in the UK, iron ore miners in the Grangesburg and Kiruna, Sweden, metal miners in the US, Navajo uranium miners in the US, Norwegian niobian and magnitite miners, South African gold and uranium miners, French uranium miners, zinc-lead miners in Sweden and a variety of small studies of environmental exposure. An analysis of the epidemiological studies reveals a variety of interpretation problem areas. The major and almost universal problem is in estimating exposure levels. In many cases there were no direct measurements of radon or radon progeny and the exposure levels are estimates based on irregular measurements and known levels in nearby mines. Perhaps the most important variable or complicating factor in the determination of the risk due to radon exposure is the confounding factor of exposure to cigarette smoke. The general scientific concensus is that, although the interaction could be somewhere between linear and supramultiplicative, it is likely a combination, and closer to multiplicative. A number of other complexities contribute to the uncertainty in the risk estimates, likely to a lesser degree than those of exposure measurements and cigarette smoke confounding.(ABSTRACT TRUNCATED AT 400 WORDS)

Air Pollutants↗
PubMed2004

Radon-induced lung cancer in French and Czech miner cohorts described with a two-mutation cancer model.

A two-mutation carcinogenesis model with clonal expansion of pre-malignant cells is used to describe lung cancer mortality data from studies on French and Czech miners with relatively low exposures to radon. The aim was to derive radon-induced lung cancer risk estimates applicable to different populations using a model description consistent with both cellular dose-response relationships, and previous model analyses of animal and human epidemiological data. The significantly different baseline lung cancer risks for the two cohorts that include the effects from the unknown smoking habits, are described with different background model parameters. A uniform description of the effect of radon for both miner cohorts is achieved by applying the same multiplicative effect for radon on the background mutation rates in the model. Incorporating the effects of decreased cellular proliferation at very advanced age improves the description of the baseline lung cancer risk, but does not lead to significant changes in the estimated radiation parameters. Here, a multi-stage model demonstrates the possibility of transferring radon-induced lung cancer risks across populations. The inherent age-time dose-rate relationships in the model allow for extrapolation to lifelong exposures to residential radon concentrations. The resulting cumulated (lifetime) risks from continuous exposure to low-level radon concentrations were found to agree with the results of the BEIR VI models.

Algorithms↗
PubMedDate not supplied

Adaptive response of human lymphocytes for the repair of radon-induced chromosomal damage.

In human lymphocytes low doses of X-rays can decrease the number of chromatid deletions induced by subsequent high doses of sparsely ionizing X-rays. Because of the concern with the carcinogenic effects of low doses of alpha-particles from radon in homes, experiments were carried out to see if low doses of X-rays could also decrease the yield of chromosomal aberrations induced by subsequent exposure to radon. Human peripheral blood lymphocytes were irradiated with low doses of X-rays (2 cGy) at 48 h of culture, exposed to radon at 72 h of culture, and analyzed for the presence of chromatid aberrations at subsequent intervals. The frequency of chromatid aberrations induced by radon alone increased with time after exposure, indicating exaggerated differences in the stage sensitivity of cell cycle stages to high-LET radiation. Furthermore, the numbers of aberrations per cell did not follow a Poisson distribution but were over dispersed, as might be expected since high-LET radiations have a high relative biological effectiveness compared with low-LET radiations. Nevertheless, lymphocytes exposed to 2 cGy of X-rays before radon exposure contained approximately one-half the number of chromatid deletions compared with lymphocytes treated with radon alone and analyzed at the same time. Thus, the putative chromosomal repair mechanism induced by low doses of sparsely ionizing radiation is also effective in reducing chromosomal aberrations induced by radon, which hitherto had been thought to be relatively independent of repair processes.

Adaptation, Physiological↗
PubMed1985

Theoretical aspects of the design of a passive radon dosemeter.

Some mathematical aspects of the development and design of a passive radon dosemeter are considered. In particular, a mathematical model is presented that is concerned with the gaseous diffusion of radon into a confined region bounded by a plastic material of known diffusion coefficient. The relationship between the time-integrated radon concentrations, inside and outside a sealed plastic container are derived. Estimates of the exposure of people to radon can be made using the time integrated radon concentration inside a calibrated container containing a CR-39 etched-track device. As a consequence of the analysis, it is possible to design a passive radon dosemeter that will be accurate, resistant to moisture and whose response will be independent of rapid variations in radon concentration. The possibility of using a container of this type for the measurement of diffusion coefficients is discussed.

Humans↗
PubMed1991

Indoor radon measurements in the Beijing area.

Average indoor air radon concentration of 30 Bq/m3 was determined in various types of dwellings in the Beijing area using activated carbon detectors. In this study, several related factors were also investigated: radon area exhalation rates of 136 building materials and from soil surfaces; Ra-226 contents of 143 soil samples, 34 building materials and 28 coal samples; and radon concentrations in gaseous fuel, outdoor air and drinking water. The magnitude and relative importance of different sources in terms of indoor radon are discussed, compared and evaluated. The results show that the underlying soil and building materials are important sources of indoor radon. Cracks in floors or walls are major pathways for the entry of radon into houses. Measurements of the annual effective dose equivalent from radon daughters for different types of aboveground and underground buildings gave average values of 1.1 and 1.5 mSv, respectively.

Air Pollution, Indoor↗
PubMed1994

Radon levels inside residences in Swaziland.

Time-integrated measurements of environmental radiation levels are commonly carried out using solid state nuclear track detectors (SSNTDs). These detectors are particularly suitable for monitoring indoor radiation. Levels of radon were measured, during winter and summer seasons, inside 130 traditional and modern houses and multi-family apartment buildings. The traditional houses, modern houses and apartment buildings had average radon levels of 62 Bq.m-3, 125 Bq.m-3 and 133 Bq.m-3, respectively. Between the ground and second floor of the apartment buildings, radon levels diminished by a factor of more than three which indicates that entry of radon-bearing soil gas was largely responsible for the higher concentration of radon in the ground floor. The radon levels in winter exceeded by approximately 30% the radon levels during summer. From the experimental data the equilibrium factor (F) and the effective dose equivalent (HE) were also obtained.

Air Pollution, Indoor↗
PubMed2004

Radon concentration in hospital buildings erected during the last 40 years in Białystok, Poland.

The aim of the study was to compare radon concentrations in neighbouring hospital buildings which were constructed in different years during the period 1963-2000 and are located in areas with similar radon potential. The value of arithmetic mean (AM) radon concentration in soil gas amounted to 14,464 Bq m(-3). In a hospital built 40 years ago, the AM radon concentration in the cellar was 38.4+/-36.7 Bq m(-3) and on higher levels it was 17.1+/-10.3 Bq m(-3). In a hospital built 16 years ago, these values equaled 45.5+/-47.2 Bq m(-3) and 20.4+/-12.5 Bq m(-3), respectively. In the newest hospital, built three years ago, radon concentration (AM) in a cellar was 32.3+/-27.4 Bq m(-3) and the respective value on higher levels amounted to 20.4+/-12.6 Bq m(-3). When comparing radon concentrations in the cellars, no statistically significant differences were found. Similarly, no statistically significant differences were observed between radon concentrations measured on higher levels in investigated hospital buildings.

Air Pollutants, Radioactive↗
PubMed2005

Mitigation of a radon-rich Belgian dwelling using active subslab depressurization.

In a radon prone area in Belgium, a dwelling with high indoor radon concentrations was identified through a passive measurement. Next, a continuous, active radon monitoring device was installed for one month. A 20-a retrospective radon assessment was also performed. The house was subsequently mitigated through active subslab depressurization with a radial fan. Afterwards the dwelling was actively monitored for several more months to observe the effects of the mitigation and to study the effect of reducing the fan power. Dose evaluations were made to evaluate the health benefit of the mitigation. It was seen that the results of the three measuring techniques before mitigation all yielded between 1700 and 2000 Bq/m3. Clear diurnal radon variations showed up only after mitigation. After mitigation, the average radon concentration fell to less than 200 Bq/m3. The yearly average dose was reduced from potentially 45 mSv/y to less than 4.5 mSv/y through mitigation. Reducing fan power to 50% did not clearly influence the amount of radon entering into the dwelling.

Air Pollution, Indoor↗
PubMed2006

High natural radiation exposure in radon spa areas: a detailed field investigation in Niska Banja (Balkan region).

The measurement campaigns have been done in the rural community of Niska Banja, a spa town located in southern Serbia, to evaluate population exposure to natural radioactivity. After a screening survey in 200 houses, annual radon and thoron concentrations were measured in 34 houses, and in 2004 a detailed investigation was carried out at six houses with elevated indoor radon concentrations. The paper presents the results of these detailed measurements. The complementary techniques were applied to determine radon and thoron concentrations in indoor air, in soil gas, radon exhalation from soil, soil permeability, and indoor and outdoor gamma doses. Soil and water samples were collected and analysed in the laboratory. Indoor radon and thoron concentrations were found to be more than 1kBqm(-3) and 200Bqm(-3), respectively. Extremely high concentrations of soil-gas radon (>2000kBqm(-3)) and radon exhalation rates (1.5mBqm(-2)s(-1)) were observed. These results will be utilised to set up the methodology for a more systematic investigation.

Air Pollution, Indoor↗
PubMed2001

Indoor radon concentrations caused by construction materials in 23 workplaces.

The aim of this study was to compare the measured and the calculated concentrations of indoor radon caused by building materials at 23 workplaces. The measured concentrations of radon were clearly higher than the calculated radon concentrations from the building materials, which indicated that the main source of indoor radon was the soil under and around the buildings. The highest means of continuously (933 Bq m(-3)) and integrated (169 Bq m(-3)) measured and calculated (from 70 to 169 Bq m(-3)) concentrations of radon were found in hillside locations. On the other hand, the median (27 and 43 Bq m(-3)) and maximum (626 and 1002 Bq m(-3)) values of calculated indoor radon concentrations exhaled from construction materials were the highest at the ground level places. On average, only 7-19% of the radon seemed to originate from the construction materials.

Air Pollution, Indoor↗
PubMed2002

Radon level in dwellings and its correlation with uranium and radium content in some areas of Himachal Pradesh, India.

LR- 115 plastic track detectors have been used to measure indoor radon level in some dwellings of Una district, Himachal Pradesh, India. The annual average radon concentration in dwellings in most of the villages falls in the range of the action level recommended by the International Commission on Radiological Protection. The radon values in some of the dwellings exceed the action level and may be unsafe from the health hazard point of view. The indoor radon values are in general higher in winter than in summer. Uranium, radium and radon exhalation studies have also been carried out in soil samples collected from these areas. A good correlation is obtained between uranium concentration in the soil and indoor radon in dwellings. The soil radon exhalation rate also correlates with the uranium concentration in soil.

Air Pollution, Indoor↗
PubMed2002

Study of a predictive methodology for quantification and mapping of the radon-222 exhalation rate.

We propose a new methodology for predicting areas with a strong potential for radon (222Rn) exhalation at the soil surface. This methodology is based on the Rn exhalation rate quantification, starting from a precise characterisation of the main local geological and pedological parameters that control the radon source and its transport to the soil/atmosphere interface. It combines a cross mapping analysis of these parameters into a geographic information system with a model of the Rn vertical transport by diffusion in the soil. The rock and soil chemical and physical properties define the entry parameters of this code (named TRACHGEO) which calculates the radon flux density at the surface. This methodology is validated from in situ measurements of radon levels at the soil/atmosphere interface and in dwellings. We apply this approach to an area located in western France and characterised by a basement displaying a heterogeneous radon source potential, as previously demonstrated by lelsch et al. (J. Environ. Radioactivity 53(1) (2001) 75). The new results obtained show that spatial heterogeneity of pedological characteristics in addition to basement geochemistry--must be taken into account to improve the mapping resolution. The TRACHGEO forecasts explain the Rn exhalation variability on a larger scale and in general correlate well with in situ observations. Moreover, the radon-prone sectors identified by this approach generally correspond to the location of the dwellings showing the highest radon concentrations.

France↗
PubMed2003

Detection of 210Po on filter papers 16 years after use for the collection of short-lived radon progeny in a room.

Radon gas was allowed to accumulate in its radium source and then injected into a 36 m(3) test room, resulting in an initial radon concentration of 15 kBq m(-3). Filter papers were used to collect the short-lived radon progeny and thus to measure the Potential Alpha Energy Concentration (PAEC) in-situ in the year 1984 at different times and conditions according to the experimental design. The radon progeny collected on the filter papers were studied as a function of aerosol particle concentration ranging from 10(2)-10(5) particles cm(-3) in three different experiments. The highest aerosol particle concentration was generated by indoor cigarette smoking. Those filters were stored after the experiment, and were used after 16 years to study the activity of the radon long-lived alpha emitter progeny, (210)Po (T(1/2)=138 days). This isotope is separated from the short-lived progeny by (210)Pb beta emitter with 22.3 years half-life. After 16 years' storage of these filters, each filter paper was sandwiched and wrapped between two CR-39 nuclear track detectors, to put the detectors in contact with the surfaces of different filters, for 337 days. Correlation between the PAEC measured using filter papers in the year 1984 and the activity of long-lived alpha emitter (210)Po on the same filter papers measured in the year 2000 were studied. The results of the (210)Po activity showed a very good correlation of 0.92 with the PAEC 16 years ago. The results also depict that the PAEC and (210)Po activity in indoor air increased with the increase of aerosol particle concentration, which shows the attachment of short-lived radon progeny with the aerosol particles. The experiment proves that indoor cigarette smoking is a major source of aerosol particles carrying radon progeny and, thus, indoor cigarette smoking is an additional source of internal radiation hazard to the occupants whether smoker or non-smoker.

Aerosols↗
PubMed2003

Radon levels in Cyprus.

Radon levels in atmospheric and aquatic systems in Cyprus have recently been measured using the radon monitor Alpha Guard. Indoor and outdoor radon levels were obtained in situ, whereas analysis of radon concentrations in water was performed using tap and ground water samples collected from several areas of the island. The average value for outdoor and indoor radon concentration is 11+/-10 and 7+/-6 Bq m(-3), respectively, and for tap and ground water 0.4 Bq l(-1) and 1.4 Bq l(-1), respectively. From these data the annual dose equivalent of airborne radon to the Cypriot population is about 0.19 mSv y(-1), which is quite low compared to the total dose equivalent of natural and man-made ionising radiation in Cyprus. Radon levels in aquatic systems are relatively low due to an exhaustive utilisation of ground water resources and also to the increased input of desalinated sea water in the water distribution network and eventually into the ground water reservoirs.

Air Pollutants, Radioactive↗
PubMed2003

Assessing radon concentrations in areas with few measurements.

The New York State Department of Health has estimated and mapped radon concentrations for every town and city in the State. Since for many towns there are few indoor radon measurements, the radon estimates for these towns were determined using correlations to surficial geology. A project was conducted to target towns for additional measurements that currently have few data but, based on the surficial geology of the town, are estimated to have elevated levels of indoor radon. The objective of the project was to obtain at least 30 additional measurements for the targeted towns and to compare the measurement results with the estimates based on geology. The study completed 1606 radon measurements from 9080 detector applications mailed to home owners in 94 underserved towns spread throughout the State. Of the 1115 basement measurements, 43% 148 Bq m(-3), with a maximum of 6900 Bq m(-3). Three homes measured in one town had radon concentrations above 2900 Bq m(-3). Of the 491 living-area measurements, 19% exceeded 148 Bq m(-3), with a maximum of 2700 Bq m(-3). About 60% and 86% of measurement results were within one standard deviation and a factor of two, respectively, of estimated concentrations. Results indicate that regardless of the magnitude of radon potential, the estimates are in good agreement with measured concentrations.

Cities↗
PubMed2002

Do low dose-rate bystander effects influence domestic radon risks?

PURPOSE: Radon risks derive from exposure of bronchio-epithelial cells to high-linear energy transfer (LET) alpha-particles. alpha-particle exposure can result in bystander effects, where irradiated cells emit signals resulting in damage to nearby unirradiated bystander cells. This can result in non-linear dose-response relations, and inverse dose-rate effects. Domestic radon risk estimates are currently extrapolated from miner data, which are at both higher doses and higher dose-rates, so bystander effects on unhit cells could play a large role in the extrapolation of risks from mines to homes. Therefore, we extend an earlier quantitative mechanistic model of bystander effects to include protracted exposure, with the aim of quantifying the significance of the bystander effect for very prolonged exposures. MATERIALS AND METHODS: A model of high-LET bystander effects, originally developed to analyse oncogenic transformation in vitro, is extended to low dose-rates. The model considers radiation response as a superposition of bystander and linear direct e It attributes bystander effects to a small subpopulation of hypersensitive cells, with the bystander contribution dominating the direct contribution at very low acute doses but saturating as the dose increases. Inverse dose-rate effects are attributed to the replenishment of the hypersensitive subpopulation during prolonged irradiation. RESULTS: The model was fitted to dose- and dose-rate-dependent radon-exposed miner data, suggesting that one directly hit target bronchio-epithelial cell can send bystander signals to about 50 neighbouring target cells. The model suggests that a naïve linear extrapolation of radon miner data to low doses, without accounting for dose-rate, would result in an underestimation of domestic radon risks by about a factor of 4, a value comparable with the empirical estimate applied in the recent BEIR-VI report on radon risk estimation. CONCLUSIONS: Bystander effects represent a plausible quantitative and mechanistic explanation of inverse dose-rate effects by high-LET radiation, resulting in non-linear dose-response relations and a complex interplay between the effects of dose and exposure time. The model presented provides a potential mechanistic underpinning for the empirical exposure-time correction factors applied in the recent BEIR-VI for domestic radon risk estimation.

Air Pollution, Indoor↗
PubMed1989

Transformation of lung cells from inhalation of radon daughters in dwellings: a preliminary study.

There is now world-wide concern for the quantification of lung cancer risk due to indoor radon, but the recent estimates are based on epidemiological studies of miners alone. The present attempt is a preliminary study of the alteration of lung stem cells irradiated by alpha particles emitted by radon daughters. Local energy deposited has been calculated for alpha particles, emitted from radon daughters lining the mucous layer in the respiratory tracts. This calculation has then been followed by dose evaluation and estimation of transformation of lung cells as a function of age. Mean life span of the stem cells was varied between 5 and 45 years to simulate living conditions in different environments. The cumulative fraction of transformed cells after 40 and 70 years has been calculated for radon concentration in the range 23-230 Bq/m3. Increase of the fraction of transformed cells with radon concentration was exponential. It has been assumed that causes other than radiation increase the rate of cell death of mature and stem lung cells, and hence the turnover of stem cells to replace them. It is concluded that the rate of transformation of cells is small for low radon concentration even late in age for non-polluted environments. For radon concentrations of 50 and 100 Bq/m3 the fractions of transformed cells are 0.2 and 6 per cent, respectively for an exposure time of 70 years.

Age Factors↗