Showing papers by "Margot Tirmarche published in 1995"

Lung Cancer in Radon-Exposed Miners and Estimation of Risk From Indoor Exposure

Abstract: Background : Radioactive radon is an inert gas that can migrate from soils and rocks and accumulate in enclosed areas, such as homes and underground mines. Studies of miners show that exposure to radon decay products causes lung cancer. Consequently, it is of public health interest to estimate accurately the consequences of daily, low-level exposure in homes to this known carcinogen. Epidemiologic studies of residential radon exposure are burdened by an inability to estimate exposure accurately, low total exposure, and subsequent small excess risks. As a result, the studies have been inconclusive to date. Estimates of the hazard posed by residential radon have been based on analyses of data on miners, with recent estimates based on a pooling of four occupational cohort studies of miners, including 360 lung cancer deaths. Purpose : To more fully describe the lung cancer risk in radon-exposed miners, we pooled original data from 11 studies of radon-exposed underground miners, conducted a comprehensive analysis, and developed models for estimating radon-associated lung cancer risk. Methods : We pooled original data from 11 cohort studies of radon-exposed underground miners, including 65 000 men and more than 2700 lung cancer deaths, and fit various relative risk (RR) regression models. Results : The RR relationship for cumulative radon progeny exposure was consistently linear in the range of miner exposures, suggesting that exposures at lower levels, such as in homes, would carry some risk. The exposure-response trend for never-smokers was threefold the trend for smokers, indicating a greater RR for exposure in never-smokers. The RR from exposure diminished with time since the exposure occurred. For equal total exposure, exposures of long duration (and low rate) were more harmful than exposures of short duration (and high rate). Conclusions: In the miners, about 40% of all lung cancer deaths may be due to radon progeny exposure, 70% of lung cancer deaths in never-smokers, and 39% of lung cancer deaths in smokers. In the United States, 10% of all lung cancer deaths might be due to indoor radon exposure, 11% of lung cancer deaths in smokers, and 30% of lung cancer deaths in never-smokers. This risk model estimates that reducing radon in all homes exceeding the U. S. Environmental Protection Agency's recommended action level may reduce lung cancer deaths about 2%-4%. These estimates should be interpreted with caution, because concomitant exposures of miners to agents such as arsenic or diesel exhaust may modify the radon effect and, when considered together with other differences between homes and mines, might reduce the generalizability of findings in miners. [J Natl Cancer Inst 87 :817-827, 1995]

Radon and Cancers Other Than Lung Cancer in Underground Miners: a Collaborative Analysis of 11 Studies

Abstract: Background: Exposure to the radioactive gas radon and its progeny (222Rn and its radioactive decay products) has recently been linked to a variety of cancers other than lung cancer ingeographic correlation studies of domestic radon exposure and in individual cohorts of occupationally exposed miners. Purpose: This study was designed to characterize further the risks for cancers other than lung cancer (i.e., non-lung cancers) from atmospheric radon. Methods: Mortality from non-lung cancer was examined in a collaborative analysis of data from 11 cohorts of underground miners in which radon-related excesses of lung cancer had been established. The study included 64 209 men who were employed in the mines for 6.4 years on average, received average cumulative exposures of 155 working-level months (WLM), and were followed for 16.9 years on average. Results: For all non-lung cancers combined, mortality was close to that expected from mortality rates in the areas surrounding the mines (ration of observed to expected deaths (O/E) = 1.01; 95% confidence interval (CI) = 0.95–1.07, based on 1179 deaths), and mortality did not increase with increasing cumulative exposure. Among 28 individual cancer categories, statistically significant increases in mortality for cancers of the stomach (O/E = 1.33; 95% CI = 1.16–1.52) and liver (O/E = 1.73; 95% CI = 1.29–2.28) and statistically significant decreases for cancers of the tongue and mouth (O/E = 0.52; 95% CI = 0.26–0.93), pharynx (O/E = 0.5; 95% CI = 0.16–0.66), and colon (O/E = 0.77; 95% CI = 0.63–0.95) were observed. For leukemia, mortality was increased in the period less than 10 years since starting work (O/E = 1.93; 95% CI = 1.19–2.95) but not subsequently. For none of these diseases was mortality significantly related to cumulative exposure. Among the remaining individual categories of non-lung cancer, mortality was related to cumulative exposure only for cancer of the pancreas (excess relative risk per WLM = 0.07%; 95% CI = 0.01–0.12) and, in the period less than 10 years since the start of employment, for other and unspecified cancers (excess relative risk per WLM = 0.22%; 95% CI = 0.08–0.37). Conclusions: The increases in mortality from stomach and liver cancers and leukemia are unlikely to have been caused by radon, since they are unrelated to cumulative exposure. The association between cumulative exposure and pancreatic cancer seems likely to be a chance finding, while the association between cumulative exposure and other and unspecified cancers was caused by deaths certified as due to carcinomatosis (widespread disseminated cancer throughout the body) that were likely to have been due to lung cancers. This study, therefore, provides considerable evidence that high concentrations of radon in air do not cause a material risk of mortality from cancers other than lung cancer. Implications: Protection standards for radon should continue to be based on consideration of the lung cancer risk alone.

Radon-exposed underground miners and inverse dose-rate (protraction enhancement) effects

Abstract: Recent models for radon-induced lung cancer assume that at high levels of cumulative exposure, as experienced historically by many underground miners of uranium and other ores, the risk of lung cancer follows an inverse dose-rate (protraction enhancement) pattern. That is, for equal total dose, a greater risk is incurred by those whose total dose is accumulated at a lower rate over a longer duration than at a higher rate over a shorter duration. This inverse dose-rate effect is hypothesized to be the consequence of multiple traversals of the nucleus of a target cell by alpha particles. It has recently been concluded, however, that for low total doses, as in most residential settings, the inverse dose-rate effect should diminish and perhaps even disappear, since at very low doses the probability that more than one alpha particle would traverse a cell is small and there would be no possibility for interactions from multiple hits. Pooling original data from 11 cohort studies of underground miners, including nearly 1.2 million person-y of observation and 2,701 lung cancer deaths, we evaluate the presence of an inverse dose-rate effect and its modification by total dose. An inverse dose-rate effect was confirmed in each cohort, except one,more » and overall in the pooled data. There also appears to be a diminution of the inverse dose-rate effect below 50 Working Level Months (WLM), although analyses were necessarily hampered by a limited range of exposure rates at low total WLM. These data support both the presence of an inverse dose-rate effect, as well as its diminution at low total dose. As a consequence, assessment of risks of radon progeny exposure in homes (on average 15-20 WLM for a lifetime) using miner-based models should not assume an ever-increasing risk per unit dose. Rather, it is more appropriate to apply risk models that take into account protraction enhancement and its diminution. 23 refs., 5 figs., 2 tabs.« less

[Radon and cancer risk: epidemiological studies after occupational or domestic exposure]

Abstract: The evaluation of cancer risk after exposure to radon is mainly based on the results of uranium miners follow-up. A cohort study on the French uranium miners has demonstrated an excess of lung cancer and of larynx cancer mortality. A linear dose-response relationship has been described between the excess relative risk of lung cancer and the cumulative exposure to radon (poisson regression). This study has contributed to a joint analysis of 11 cohorts of miners, the aim being a more precise evaluation of the different factors able to influence the dose-response relationship between radon and lung cancer mortality. These factors are: age at first exposure, attained age, time since exposure, the pattern of exposure over time and tobacco consumption. The extrapolation of the risk for the general public from the risk estimated after occupational exposure, has to be considered by taking in account several remarks: uranium miners are exposed, beside radon, to two other radiological components, gamma rays and long lived uranium dust, and to other substances specific of the mines, which are absent in the domestic environment but may with radon have an effect on the lung cancer risk. It was impossible to estimate directly, from these uranium miners data, the risk linked to radon for non-smokers and for female population. A case control-study is currently be carrying out in the French hospitals, in order to estimate the risk of lung cancer linked to the last 30 years of radon exposure in the dwellings.