Margot Tirmarche

Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies

Abstract Objective To determine the risk of lung cancer associated with exposure at home to the radioactive disintegration products of naturally occurring radon gas Design Collaborative analysis of individual data from 13 case-control studies of residential radon and lung cancer. Setting Nine European countries. Subjects 7148 cases of lung cancer and 14 208 controls. Main outcome measures Relative risks of lung cancer and radon gas concentrations in homes inhabited during the previous 5-34 years measured in becquerels (radon disintegrations per second) per cubic metre (Bq/m3) of household air. Results The mean measured radon concentration in homes of people in the control group was 97 Bq/m3, with 11% measuring > 200 and 4% measuring > 400 Bq/m3. For cases of lung cancer the mean concentration was 104 Bq/m3. The risk of lung cancer increased by 8.4% (95% confidence interval 3.0% to 15.8%) per 100 Bq/m3 increase in measured radon (P = 0.0007). This corresponds to an increase of 16% (5% to 31%) per 100 Bq/m3 increase in usual radon—that is, after correction for the dilution caused by random uncertainties in measuring radon concentrations. The dose-response relation seemed to be linear with no threshold and remained significant (P = 0.04) in analyses limited to individuals from homes with measured radon < 200 Bq/m3. The proportionate excess risk did not differ significantly with study, age, sex, or smoking. In the absence of other causes of death, the absolute risks of lung cancer by age 75 years at usual radon concentrations of 0, 100, and 400 Bq/m3 would be about 0.4%, 0.5%, and 0.7%, respectively, for lifelong non-smokers, and about 25 times greater (10%, 12%, and 16%) for cigarette smokers. Conclusions Collectively, though not separately, these studies show appreciable hazards from residential radon, particularly for smokers and recent ex-smokers, and indicate that it is responsible for about 2% of all deaths from cancer in Europe.

Cancer consequences of the Chernobyl accident: 20 years on

26 April 2006 marks the 20th anniversary of the Chernobyl accident. On this occasion, the World Health Organization (WHO), within the UN Chernobyl Forum initiative, convened an Expert Group to evaluate the health impacts of Chernobyl. This paper summarises the findings relating to cancer. A dramatic increase in the incidence of thyroid cancer has been observed among those exposed to radioactive iodines in childhood and adolescence in the most contaminated territories. Iodine deficiency may have increased the risk of developing thyroid cancer following exposure to radioactive iodines, while prolonged stable iodine supplementation in the years after exposure may reduce this risk. Although increases in rates of other cancers have been reported, much of these increases appear to be due to other factors, including improvements in registration, reporting and diagnosis. Studies are few, however, and have methodological limitations. Further, because most radiation-related solid cancers continue to occur decades after exposure and because only 20 years have passed since the accident, it is too early to evaluate the full radiological impact of the accident. Apart from the large increase in thyroid cancer incidence in young people, there are at present no clearly demonstrated radiation-related increases in cancer risk. This should not, however, be interpreted to mean that no increase has in fact occurred: based on the experience of other populations exposed to ionising radiation, a small increase in the relative risk of cancer is expected, even at the low to moderate doses received. Although it is expected that epidemiological studies will have difficulty identifying such a risk, it may nevertheless translate into a substantial number of radiation-related cancer cases in the future, given the very large number of individuals exposed.

Lung Cancer Risk from Radon and Progeny and Statement on Radon

Recent epidemiological studies of the association between lung cancer and exposure to radon and its decay products are reviewed. Particular emphasis is given to pooled case-control studies of residential exposures, and to cohorts of underground miners exposed to relatively low levels of radon. The residential and miner epidemiological studies provide consistent estimates of the risk of lung cancer, with significant associations observed at average annual concentrations of approximately 200 Bq/m³ and cumulative occupational levels of approximately 50 working level months (WLM), respectively. Based on recent results from combined analyses of epidemiological studies of miners, a lifetime excess absolute risk of 5 × 10⁻⁴ per WLM [14 × 10⁻⁵ per (mJh/m³)] should now be used as the nominal probability coefficient for radon- and radon-progeny-induced lung cancer, replacing the previous Publication 65 (ICRP, 1993) value of 2.8 × 10⁻⁴ per WLM [8 × 10⁻⁵ per (mJh/m³)]. Current knowledge of radon-associated risks for organs other than the lungs does not justify the selection of a detriment coefficient different from the fatality coefficient for radon-induced lung cancer. Publication 65 (ICRP, 2003) recommended that doses from radon and its progeny should be calculated using a dose conversion convention based on epidemiological data. It is now concluded that radon and its progeny should be treated in the same way as other radionuclides within the ICRP system of protection; that is, doses from radon and its progeny should be calculated using ICRP biokinetic and dosimetric models. ICRP will provide dose coefficients per unit exposure to radon and its progeny for different reference conditions of domestic and occupational exposure, with specified equilibrium factors and aerosol characteristics.

Human exposure to high natural background radiation: what can it teach us about radiation risks?

Natural radiation is the major source of human exposure to ionising radiation, and its largest contributing component to effective dose arises from inhalation of (222)Rn and its radioactive progeny. However, despite extensive knowledge of radiation risks gained through epidemiologic investigations and mechanistic considerations, the health effects of chronic low-level radiation exposure are still poorly understood. The present paper reviews the possible contribution of studies of populations living in high natural background radiation (HNBR) areas (Guarapari, Brazil; Kerala, India; Ramsar, Iran; Yangjiang, China), including radon-prone areas, to low dose risk estimation. Much of the direct information about risk related to HNBR comes from case-control studies of radon and lung cancer, which provide convincing evidence of an association between long-term protracted radiation exposures in the general population and disease incidence. The success of these studies is mainly due to the careful organ dose reconstruction (with relatively high doses to the lung), and to the fact that large-scale collaborative studies have been conducted to maximise the statistical power and to ensure the systematic collection of information on potential confounding factors. In contrast, studies in other (non-radon) HNBR areas have provided little information, relying mainly on ecological designs and very rough effective dose categorisations. Recent steps taken in China and India to establish cohorts for follow-up and to conduct nested case-control studies may provide useful information about risks in the future, provided that careful organ dose reconstruction is possible and information is collected on potential confounding factors.

Radon Exposure And The Risk Of Leukemia: A Review Of Epidemiological Studies

Since the 1990s, several authors estimated that radon inhalation may deliver a small amount of irradiation to the red bone marrow, and consequently may increase the risk of leukemia in humans. The objective of this review is to conduct a critical analysis of epidemiologic results currently available concerning the relationship between radon exposure and the risk of leukemia. Nineteen ecological studies, six miner cohort studies, and eight case-control studies published between 1987 and 2000 are included in this review. The limitations associated with each of these studies are discussed. The results of the ecological studies are relatively concordant and suggest an association between radon concentrations and the risk of leukemia at a geographic level. But these ecological studies present important limitations, and some are only crude analyses. Moreover, the results of the cohort and case-control studies, based on individual data, do not show any significant association between radon exposure and leukemia risk. Our conclusion is that the overall epidemiologic results currently available do not provide evidence for an association between radon exposure and leukemia.

Lung cancer in French and Czech uranium miners: Radon-associated risk at low exposure rates and modifying effects of time since exposure and age at exposure.

Abstract Tomasek, L., Rogel, A., Tirmarche, M., Mitton, N. and Laurier, D. Lung Cancer in French and Czech Uranium Miners: Radon-Associated Risk at Low Exposure Rates and Modifying Effects of Time since Exposure and Age at Exposure. Radiat. Res. 169, 125–137 (2008). Radon is recognized as a public health concern for indoor exposure. Precise quantification derived from occupational exposure in miners is still needed for estimating the risk and the factors that modify the dependence on cumulated exposure. The present paper reports on relationship between radon exposure and lung cancer risk in French and Czech cohorts of uranium miners (n = 10,100). Miners from these two cohorts are characterized by low levels of exposure (average cumulated exposure of less than 60 WLM) protracted over a long period (mean duration of exposure of 10 years) and by a good quality of individual exposure estimates (95% of annual exposures based on radon measurements). The modifying effect of the quality of exposure on the risk is analyzed. A total of 574 lung cancer deaths were observed, which is 187% higher than expected from the national statistics. This significantly elevated risk is strongly associated with cumulated radon exposure. The estimated overall excess relative risk per WLM is 0.027 (95% CI: 0.017–0.043, related to measured exposures). For age at exposure of 30 and 20 years since exposure, the ERR/WLM is 0.042, and this value decreases by approximately 50% for each 10-year increase in age at exposure and time since exposure. The present study emphasizes that the quality of exposure estimates is an important factor that may substantially influence results. Time since exposure and simultaneously age at exposure were the most important effect modifiers. No inverse exposure-rate effect below 4 WL was observed. The results are consistent with estimates of the BEIR VI report using the concentration model at an exposure rate below 0.5 WL.

Mortality risk in the French cohort of uranium miners: extended follow-up 1946-1999

Objectives: This paper presents the risk of death from lung cancer and from other causes of death for the French cohort of uranium miners through 1999 and estimates associations with radon exposure. Methods: The cohort includes men employed as uranium miners for at least 1 year between 1946 and 1990. For each miner, vital status and cause of death were obtained from the national registry, and radon exposure was reconstructed for each year. Standardised mortality ratios were computed with national mortality rates as references. Exposure–risk relationships were estimated by Poisson regression, with a linear excess relative risk (ERR) model and a 5-year lag. Results: The cohort included 5086 miners and 153 063 person-years of exposure. The mean duration of follow-up was 30.1 years. In all 4140 miners exposed to radon, the average cumulative exposure was 36.6 working level months (WLM). There were 1411 deaths of miners <85 years of age. The miners did not differ significantly in overall mortality from the general male population. The analysis confirmed an excess risk of lung cancer death (n = 159; SMR = 1.43; 95% CI: 1.22 to 1.68), which increased significantly with cumulative radon exposure (ERR per 100 WLM = 0.71; 95% CI: 0.29 to 1.35). The ERR per unit exposure was much higher after 1955, when the accuracy of exposure measurement improved substantially (ERR per 100 WLM = 2.00; 95% CI: 0.91 to 3.65). A significant excess of kidney cancer deaths was observed (n = 20; SMR = 2.0; 95% CI: 1.22 to 3.09), which was not associated with cumulative radon exposure. No excess was observed for other causes of death, except silicosis (n = 23; SMR = 7.12; 95% CI: 4.51 to 10.69). Conclusions: The analysis confirmed the excess risk of death from lung cancer associated with low radon exposure. An excess risk of death from kidney cancer was also observed, apparently not associated with cumulative radon exposure.

Indoor radon and lung cancer in France.

Background: Several case-control studies have indicated an increased risk of lung cancer linked to indoor radon exposure; others have not supported this hypothesis, partly because of a lack of statistical power. As part of a large European project, a hospital-based case-control study was carried out in 4 areas in France with relatively high radon levels. Methods: Radon concentrations were measured in dwellings that had been occupied by the study subjects during the 5- to 30-year period before the interview. Measurements of radon concentrations were performed during a 6-month period using 2 Kodalpha LR 115 detectors (Dosirad, France), 1 in the living room and 1 in the bedroom. We examined lung cancer risk in relation to indoor radon exposure after adjustment for age, sex, region, cigarette smoking, and occupational exposure. Results: We included in the analysis 486 cases and 984 controls with radon measures in at least 1 dwelling. When lung cancer risk was examined in relation to the time-weighted average radon concentration during the 5- to 30-year period, the estimated relative risks (with 95% confidence intervals) were: 0.85 (0.59–1.22), 1.19 (0.81–1.77), 1.04 (0.64–1.67), and 1.11 (0.59–2.09) for categories 50–100, 100–200, 200–400, and 400+ becquerels per cubic meter (Bq/m3), respectively (reference <50 Bq/m3). The estimated relative risk per 100 Bq/m3 was 1.04 (0.99–1.11) for all subjects and 1.07 (1.00–1.14) for subjects with complete measurements. Conclusions: Our results support the presence of a small excess lung cancer risk associated with indoor radon exposure after precise adjustment on smoking. They are in agreement with results from some other indoor radon case-control studies and with extrapolations from studies of underground miners.

An update of cancer mortality among the French cohort of uranium miners: Extended follow-up and new source of data for causes of death

The follow-up of the French cohort of uranium miners has been extended to 1994, and a new source of information for causes of death has been used. The paper presents the new results regarding the risk of death among the cohort, and analyses the impact of the methodological changes on these results. The extension of the follow-up results in a substantial increase in statistical power compared with previous analysis (+25% for person-years and +74% for the number of deaths). The use of the National Mortality Database as the principal source for causes of death allows to reduce the potential bias in the calculation of standardized mortality ratios (SMR). As a consequence, an excess risk of deaths from laryngeal cancer, suggested in the first analysis, is not confirmed. The analysis shows the existence of an excess risk of deaths from lung cancer among French uranium miners (85 observed deaths, SMR = 1.9, 95% confidence interval CI: 1.5–2.3), and an increase of this risk with cumulative exposure to radon (excess relative risk per 100 working level month = 0.6, 95% CI: 0.1–1.2). These results confirm the existence of a risk of death from lung cancer in a population chronically exposed to relatively low levels of radon.

Cancer risk in nuclear workers occupationally exposed to uranium-emphasis on internal exposure.

Workers involved in the nuclear fuel cycle have a potential for internal exposure to uranium. The present review of epidemiological studies of these workers aims to elucidate the relationship between occupational internal uranium exposure and cancer risk. Eighteen cohort and 5 nested case-control studies published since 1980 are reviewed. Workers occupationally exposed to uranium appear to be at increased risk of mortality from neoplasms of the lung, larynx, and lymphatic and haematopoietic tissue. Currently available evidence for a positive association between internal exposure to uranium and the risk of cancer is limited. The common weaknesses in reviewed studies include low statistical power and inaccurate assessment of internal exposure to uranium. Further investigations should focus on precise assessment of occupational exposure and address the issue of potential confounders.