Epidemiological associations among lung cancer,radon exposure and elevation above sea level--a reassessment of Cohen''s county level radon study

Inhalation of radon (222Rn) decay products by persons living in homes has been associated with increased risk of lung cancer. Some epidemiological studies have shown a positive association between radon exposure and lung cancer rates. However, a large U.S.-wide ecological study (Cohen 1995) has shown a clear inverse association between average county radon concentration in homes and average lung cancer rates in the county. Cohen's strong inverse association between radon and lung cancer is surprising since there is no plausible biological reason for an inverse causal relationship between the two. We plot the county average lung cancer rate vs. the elevation above sea level (altitude) and show an inverse association between county average lung cancer rate and elevation. The elevation used for each county is the altitude of the most populous place in the county. We postulate that the decrease in lung cancer rates with higher elevations is caused by the carcinogenic effect of higher absolute oxygen concentration in the inspired air at lower elevations. Stratifying Cohen's lung cancer vs. radon data into ten groups of counties with similar elevations removes some, but not all, of his inverse association between radon and lung cancer.     

Interaction of alpha particles with bronchial cells

The alpha-activity on the bronchial airways has been calculated for 222Rn daughter exposures producing observable excess bronchogenic lung cancer in underground miners. The activity distribution of aerosol particles with attached 222Rn daughters on the bronchial tree is truly diffuse because of the short half-life of the daughters and the large number of particles in the ambient aerosol. From the bronchial airway activity and the minor epidemiology, it can be shown that it requires, on average, 4 X 10(9) stem cells in bronchial epithelium to be hit in order to produce an observed lung cancer. For very high 222Rn daughter exposures of miners, multiply hit cells are highly probable; yet the lung cancer response is lower per unit exposure at high exposures than for mining exposures--near those sustained in the environment probably due to stem cell death. A knowledge of the number of multiply hit cells in miners permits some infererences to be made about the effectiveness of particulate versus diffusely distributed alpha emitters in the lung, namely, that particulates should not be significantly more effective in lung cancer induction than a diffuse distribution.     

Determining the 222Rn exhalation rate of building materials using liquid scintillation counting

A new method for determining the free 222Rn exhalation rate from building materials is described. The sample is enclosed in a container from which the exhaled Rn is continuously purged by nitrogen gas. After 2-3 h, when the Rn level in the container has reached a steady-state concentration, the outflowing Rn is trapped on silica gel at about -190 degrees C. About 16 h after sampling, the silica gel is analyzed by liquid scintillation counting to determine the area exhalation rate. The method described has a good repeatability and reproducibility with coefficients of variation of 7.8% and 8.3%, respectively, at 5 Bq m-2 h-1. The low limit of detection of 11 mBq 222Rn offers the opportunity to quantify the exhalation rate of almost all kinds of building materials. It was found that the air humidity strongly influences the exhalation rates of building material and, therefore, should be controlled. Two typical building materials were investigated. For gypsum, an increase in the exhalation rate with increasing water vapor pressure was found, whereas for concrete, a linear decrease with increasing water vapor pressure was observed. The 222Rn area exhalation rates of 20 Dutch building materials, including some experimental ones, were determined at 50% RH, 20 degrees C, showing a range of less than 0.02-15.8 Bq m-2 h-1. The lowest values were found for natural gypsum board, the highest for phosphogypsum blocks. Building materials containing fly ash gave area exhalation rates comparable to those of similar materials without fly ash.     

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.     

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.     

Indoor radon levels in the northeastern U.S.: effects of energy-efficiency in homes

The expectation of elevated 222Rn levels in modern homes that have low air interchange rates with the out-of-doors caused us to survey both solar and conventional homes in northeastern New York State. The solar homes as a group have three times the 222Rn levels of the conventional homes, and specific problems exist that are introduced or exaggerated by modern construction. For example the highest two levels of radon in the solar homes give radiation doses over 30 yr that are known to produce lung cancer in 1% of uranium miners. Summer readings in more than half of the cases are different from winter ones by a factor of two or more, so that year-round measurements are necessary for precise dosimetry. The track etching technique is ideally suited for such measurements.     

Lung cancer risk at low doses of alpha particles

A survey of inhabitant exposures arising from the inhalation of 222Rn and 220Rn progeny, and lung cancer mortality has been carried out in two adjacent areas in Guangdong Province, People's Republic of China, designated as the "high background" and the "control" area. Annual exposure rates are 0.38 working level months (WLM) per year in the high background, and 0.16 WLM/yr in the control area. In 14 yr of continuous study, from 1970 to 1983, age-adjusted mortality rates were found to be 2.7 per 10(5) living persons of all ages in the high background area, and 2.9 per 10(5) living persons in the control area. From this data, we conclude that we are unable to determine excess lung cancers over the normal fluctuations below a cumulative exposure of 15 WLM. This conclusion is supported by lung cancer mortality data from Austrian and Finnish high-background areas. A theoretical analysis of epidemiological data on human lung cancer incidence from inhaled 222Rn and 220Rn progeny, which takes into account cell killing as competitive with malignant transformation, leads to the evaluation of a risk factor which is either a linear-exponential or a quadratic-exponential function of the alpha-particle dose. Animal lung cancer data and theoretical considerations can be supplied to support either hypothesis. Thus we conclude that at our current stage of knowledge both the linear-exponential and the quadratic-exponential extrapolation to low doses seem to be equally acceptable for Rn-induced lung cancer risk, possibly suggesting a linear-quadratic transformation function with an exponential cell-killing term, or the influence of risk-modifying factors such as repair or proliferation stimuli.     

Radon-222 concentrations and decay-product equilibrium in dwellings and in the open air

Results are presented of measurements of the activity concentrations of 222Rn and its short-lived decay products and the 212Pb/212Bi concentrations in more than 200 dwellings in West Germany and in the open air. For more than 130 measurements of the equilibrium factor F in dwellings the median value was found to be 0.3. Measurements of F in the open air under various conditions resulted in a mean value of about 0.4. The results of the investigations showed that indoors F depends only slightly on ventilation, indoor 222Rn concentration and other parameters. The equilibrium factor F in the open air, however, was found to depend on meteorological conditions. Empirical correlations from the data obtained for the daughter/222Rn concentration ratios were derived to provide relations for the prediction of the individual daughter product concentrations at a measured 222Rn level. It was established that the daughter/222Rn concentration ratios for indoor air do not change within the range of 222Rn concentrations investigated (1-370 Bq X m-3). These relations, however, are not valid for the daughter/222Rn concentration ratios in outdoor air. The correlations derived further suggest that the individual daughter product concentrations may be assessed with sufficient accuracy by only measuring the 222Rn concentrations. Thus the daughter ratios obtained in this way should enable good estimates of the lung dose for members of the public due to inhalation of the short-lived 222Rn daughters and the dose contribution of the individual 222Rn-daughter products.     

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.     

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.     

广东省居民肺癌与吸入氡关系的初步探讨

本文引用我所1985年对本省居民住宅内、外氡(气土)及其短寿子体浓度调查数据及1982年全省居民人口普查统计资料,采用挪威学者Stranden氏提出的氡与肺癌关系的估算模式,对广东省居民肺癌与吸入氡及其子体的关系进行了分析讨论,得出全部肺癌发病因素中由暴露氡所致份额为11.3%。     

Alpha-particle-induced cancer in humans

Updated information is given on alpha-particle-induced cancer in persons internally exposed to 222Rn progeny, Thorotrast, long-lived 226Ra and 228Ra, and short-lived 224Ra. The lung cancer risk to persons breathing 222Rn progeny in the indoor air of offices, schools, and homes is of increasing concern. About half of the recent deaths among the German Thorotrast patients have been from liver cancer. Animal studies indicate that the liver cancer risk from Thorotrast is mainly from its radioactivity and that the risk coefficient for the Thorotrast patients can be used provisionally for other alpha emitters in the human liver. Six skeletal cancers have occurred in persons with average skeletal doses between 0.85 and 11.8 Gy from 226Ra and 228Ra. In the low-dose German 224Ra patients, two skeletal sarcomas have occurred at about 0.7 Gy compared to about six cases predicted by results from 224Ra patients at higher doses. The minimal appearance time for radiation-induced bone sarcomas in humans is about 4 y. Following brief irradiation, the vast majority of induced bone sarcomas are expressed by about 30 y. Recent evidence against the "practical threshold" hypothesis is given. With the downward revision of neutron doses to the atomic-bomb survivors, the follow-up of persons exposed to alpha particles may be the best opportunity to evaluate directly the effects of high LET radiation on humans.     

Radiation Exposure and Dose to Small Mammals in Radon-Rich Soils

Protection of the environment from radionuclide releases requires knowledge of the normal background levels of radiation exposure in the exposed biotic community and an estimate of the detriment caused by additional exposure. This study modeled the background exposure and dose to the lungs of small burrowing mammals from ²²²Rn in artificial burrows in radon-rich soils at a site in southeastern Manitoba. E-PERM chambers used to measure ²²²Rn in soil showed good reproducibility of measurement, with an average coefficient of variance (CV) of about 10%. Geometric mean (GM) ²²²Rn concentrations at nine randomly selected sites ranged from 5,490 Bq/m³ (GSD = 1.57, n = 7) to 41,000 Bq/m³ (GSD = 1.02, n = 5). Long-term monitoring of ²²²Rn concentrations in artificial burrows showed large variation within and between burrows and did not show consistent variation with season, orientation of the burrow opening, or levels of ²²⁶Ra in the soil. Annual GM concentrations in individual burrows ranged from 7,480 Bq/m³ (GSD = 1.60) to 18,930 Bq/m³ (GSD = 1.81) in burrows several meters apart. A grand GM of 9,990 Bq/m³ (GSD = 1.81, n = 214) was measured over the site for the year. An exposure model was constructed for five small mammal species based on their respiration rates and the number of hours spent in the burrow, active or hibernating, exposed to soil gas ²²²Rn, and the time spent out of the burrow exposed to atmospheric ²²²Rn. A background dose of 0.9 mGy/a from atmospheric ²²²Rn (40 Bq/m³) was estimated for a large-bodied (80 kg), nonburrowing animal living on the soil surface. The highest exposures (mJ/a) in burrowing mammals occurred in those species with the highest respiration rates. Hibernation accounted for a small fraction of total annual exposure (<5%) because of very low respiration rates during this period. Absorbed dose to lung (mGy/a) was highest in the pocket gopher and decreased in the larger animals because of larger lung mass. Using mean ²²²Rn concentrations from the field studies and an equilibrium factor (F) of 0.5, doses to lung ranged from 90 mGy/a in the badger to 700 mGy/a in the pocket gopher. These doses closely correspond to those estimated from published dose conversion factors (DCFs) of 1.4 mGy per mJ · h/m³ for whole lung. For the ground squirrel, the DCF approach gives an estimated dose of 300 mGy/a versus 270 using the respiratory flow rate method. Based on these results, doses exceeding 500 mGy/a may be common in mammals and birds (i.e. the burrowing owl) living in radon-rich soils. Published risk coefficients for small mammals suggest that about 17 cancers would occur in 1,000 animals at these exposure rates. Although the potential effects from these exposures were not examined in this study, the study raises questions about how the animals may respond physiologically to this largely natural stress. Received: 25 March 1997/Accepted: 11 December 1997     

222Rn emanation from uranium-glazed ceramics

Orange-red uranium-glazed dinnerware was found to emanate 222Rn to produce an average of less than 0.1 Bq 222Rn decay per piece, which should have no associated health risks. Comparison of 222Rn emanation to 226Ra in glazes (measured by alpha spectrometry) indicated inefficient emanation (<5%) of 222Rn, consistent with the low radon levels observed and with the presence of 222Rn progeny in glazes. These studies also showed that reagent grade uranium compounds may emanate measurable 222Rn.     

Radon-222 on the island of Hawaii

The island of Hawaii, like other locations in a marine environment, has low levels of atmospheric 222Rn. The low concentrations of 222Rn and its decay products result from a low average flux density of 9.8 mBq m-2 s-1, the mixing of marine air from the Pacific having a 222Rn concentration of only 0.04 Bq m-3 with air from over the island, and the decay of 222Rn as it is transported in air masses across the Pacific primarily from the Asian continent. The overall mean concentration over the Island The overall mean concentration over the Island was found to be 0.44 Bq m-3 compared with a figure of about 8 Bq m-3 for air over continents. A consideration of the island as a source of 222Rn must take into account the relatively low average flux density associated with the lava fields and accompanying thin soils. The 222Rn formed from the U and 226Ra present in the lava cannot escape to the atmosphere. The deep agricultural soils, on the other hand, provide relatively high flux densities. When the areas of the soil types are taken into account, the exhalation for the lava fields, thin organic soils, and deep agricultural soils were 0.25, 1.7, and 32 MBq s-1, respectively. Measurements of indoor 222Rn on the island indicate levels of approximately 25 Bq m-3 which is appreciably lower than 40 Bq m-3 taken as an average for indoor levels on the mainland. Based on an assumed indoor occupancy level of 0.8, the effective dose equivalent for inhaled 222Rn and its decay products on Hawaii is 1.2 mSv y-1. This is only a little more than one-half of that for a resident of the continental United States who is estimated to receive an effective dose equivalent of 2 mSv y-1. The relatively low effective dose equivalent for the population on the island may have interesting effects in comparison with people living in areas where the inhaled dose from 222Rn is much higher.     

Atmospheric 222Rn in tourist caves of Slovenia, Yugoslavia

Radon-222 concentrations in the air of 12 tourist caves in Slovenia, Yugoslavia were measured. In almost all the caves concentrations are higher than in the outdoor air, with the highest concentration in the Tabor Cave at about 6000 Bq m-3. From the 222Rn concentrations obtained, the activity of 222Rn inhaled by a visitor breathing cave air was calculated, and the bronchial dose was estimated. The inhaled activity and the bronchial dose were highest in the Tabor Cave with values of 10 kBq and 540 microSv, respectively.     

Design issues in epidemiologic studies of indoor exposure to Rn and risk of lung cancer

Recent data on indoor air quality have indicated that Rn (222Rn) and its decay products are frequently present in domestic environments. Since studies of Rn-exposed miners have established that Rn decay products are a lung carcinogen, their presence in indoor air raises concerns about an increase in lung cancer risk for the general population. To directly evaluate lung cancer risk from domestic exposure to Rn and its decay products, as well as to evaluate risk assessments derived from studies of Rn-exposed underground miners, several epidemiologic studies of indoor Rn exposure have been initiated or are planned. This paper calculates sample sizes required for a hypothetical case-control study to address several important hypotheses and shows the impact of several difficult problems associated with estimating a subject's Rn exposure. We consider the effects of subject mobility, choice of the exposure response trend which is used to characterize an alternative hypothesis, and errors in the estimation of exposure. Imprecise estimation of Rn exposure arises from errors in the measurement device, exposure to Rn decay products from sources outside the home, inability to measure exposures over time in current as well as previous residences, and the unknown relationship between measured concentration and lung dose of alpha energy from the decay of Rn and its progeny. These methodological problems can result in large discrepancies between computed and actual study power. Failure to anticipate these problems in the design of a study can result in inaccurate estimates of power. We conclude that case-control studies of indoor Rn and lung cancer may require substantial numbers of subjects in order to address the many questions of importance that burden current risk assessments with uncertainty. We suggest pooling data from studies with the largest numbers of cases and with the most precise estimates of Rn exposure as the best approach for meeting present research needs.     

Surface radioactivity resulting from the deposition of 222Rn daughter products

Studies of indoor radiation environments typically involve measurements of 222Rn, airborne 222Rn decay products, and the degree of radioactive equilibrium. This paper describes the relationship between the 222Rn in air, and the level of surface radioactivity that results from the build-up and decay of the daughter isotope, 210Pb. Samples of 222Rn were collected from Mystery Cave, which is located in southeastern Minnesota and from the basement of a house in Minneapolis, MN. Lead-210 was measured on surfaces within the cave, on a rock removed from the cave, and on a basement window. Surface alpha activities were measured on the rock sample and on the window. Radon-222 concentrations in the cave air ranged from 3 to 13 kBq m-3. In the basement, 222Rn levels were between 0.2 and 0.4 kBq m-3. Virtually all the surface radioactivity resulted from the deposition and decay of airborne 222Rn daughter products and was not produced by the decay of U in the rock. Radon-222 concentrations in the cave air were almost 30 times higher than in the basement air; however, the surface 210Pb activity in the cave was 100 times higher than that in the basement. This suggests that in the cave air, 222Rn daughter products are more likely to reach the walls and decay to 210Pb. The measurements of surface alpha activity did not show a similar trend primarily because 210Pb had diffused further into the coating of dirt on the rock than into the glass of the window. The resulting surface activity of the rock was lower than expected based on the 210Pb concentration, because many of the alpha-emitting nuclei were at depths beyond the range of emitted alpha particles. On surfaces where the penetration range of alpha particles is greater than the diffusion depth of 210Pb atoms, either the 210Pb concentration or surface alpha-activity measurements should provide estimates of average long-term 222Rn concentrations.     

Continuous measurements of outdoor 222Rn concentrations for three years at one location in Colorado

Measurements were made of 222Rn concentrations outdoors in Ft. Collins, Colorado, using a continuously sampling scintillation flask between January 1993 and December 1995. These data were analyzed for hourly, daily, and seasonal variations. The average 222Rn concentration at 1 m above the ground was 18 +/- 10 Bq m(-3) with a geometric mean of 15 Bq m(-3) and a geometric standard deviation of 1.7. Hourly averaged data indicated a diurnal pattern with the outdoor 222Rn concentration reaching a maximum in the early morning between 4:00 a.m. and 6:00 a.m. and a broad minimum between 1:00 p.m. and 4:00 p.m. in the afternoon. An analysis also indicated that the outdoor 222Rn concentrations were consistently lowest during the spring (March and April) and highest during the late summer (July-September).     

Tests of the linear, no-threshold dose-response relationship for high-LET radiation

It is pointed out that induction of lung cancer by exposure to Rn daughters, applied at high doses to miners and at low doses to exposures in homes, provides a very stringent and sensitive test of the linear, no-threshold dose-response relationship for high-LET radiation, because this relationship predicts that a substantial fraction of lung cancer among non-smokers is due to average Rn levels. Therefore, it predicts an easily observable elevation of lung cancer rates in areas where Rn levels are many times greater than the average, especially at times before cigarette smoking began to have important effects on lung cancer statistics. While more data are needed (and will be forthcoming), some of the early indications of these studies are reviewed here. Several cases are now known where average Rn levels are very high, and in all of these cases lung cancer rates are well below average. Methods for analyzing these data are discussed, and it is concluded that, based on current evidence, they indicate at least a factor of 4 disagreement with linear, no-threshold predictions.