Failures and critique of the BEIR III lung cancer risk estimates

Radon and cancer mortality among underground uranium miners in the Příbram region of the Czech Republic

BACKGROUND

This study aims to estimate the association between radon and site-specific cancer mortality among a large contemporary cohort of male uranium miners.

METHODS

Annual occupational radon exposure was estimated based on a worker's duration of underground mining in a year and estimates of potential alpha energy of radon progeny in their location of work. Cancer mortality over the period 1977-1992 was ascertained for a cohort of 16 434 male underground uranium miners employed in the Czech Republic between 1946 and 1992. Poisson regression was used to estimate relationships between cumulative radiation exposure (in working level months [WLM]) and site-specific cancer mortality.

RESULTS

Radon is positively associated with lung cancer mortality (excess relative rate [ERR] per 100 WLM = 0.2; 95% confidence interval [CI]: 0.10, 0.37). The best fit of the dose-response relationship between radon and lung cancer mortality was linear and estimates of radon-lung cancer associations varied by windows of time-since-exposure. Positive associations between radon and several types of cancer other than lung cancer were identified, notably chronic lymphocytic leukemia (CLL) (ERR/100 WLM = 0.24; 95% CI: [not determined [ND], 5.10]) and extrathoracic cancer (ERR/100 WLM = 0.12; 95% CI: [ND, 0.69]). We observed no associations between radon and stomach cancer, nor between radon and several hematopoietic cancer subtypes.

CONCLUSIONS

This study confirms the established radon-lung cancer association and suggests that radon may also be associated with other types of cancer mortality. Further investigations of extrathoracic and CLL cancer, with the aim of obtaining more precise estimates, are warranted to understand associations between radon and cancers other than lung.

Radiation doses from radon in buildings

Not until about 1970 was it possible to estimate the magnitude of the correlation between additional lung cancer frequency and radon daughter exposure in miners. In addition, it has been realised that high levels of radon daughters in homes may be found in all countries and therefore the interest in radon in buildings has rapidly increased during the last 10 years. Radon gas enters the house from underground, from building materials and in some cases from tap water. Indoor radon daughter concentrations vary between countries and regions. The absorbed dose in the basal cells of the bronchial epithelium based on an average of the population in Canada, U.S.A. and West Germany can be estimated to be about 1 mGy a-1 (average radon daughter concentration about 25 Bq m-3) for Great Britain about half of that value and for the Nordic countries about double this value. 300-3000 lung cancer cases (most probable 1100) may occur in the future in the Swedish population of 8.4 million from radon daughter exposure indoors today. This estimation is made by the National Institute of Radiation Protection. A lower estimate of 100-1000 lung cancer cases is made by the Swedish Cancer Committee. Efforts to decrease the exposure from radon daughters indoors have been made in some countries by establishing limits or recommendations for the radon or radon daughter concentration indoors. Measuring methods for finding houses with high radon daughter concentrations and effective building techniques in order to decrease the radon daughter concentrations in both existing and for planned buildings are available.

Room for a role for radon in lung cancer causation?

Reduced ventilation due to energy saving has focussed interest on a potential lung cancer risk from increased indoor concentrations of alpha-emitting radon and radon daughters, escaping from building materials and from the ground. Some preliminary studies now also indicate a hazard to be present as related to radon daughter exposure in homes. However, the indoor radon daughter levels have probably been continuously increasing for half a century, especially in colder climates, due to the introduction of central heating instead of stoves and open fire places, reducing thermal ventilation. Furthermore, in our time, many people have got additional exposure through extended indoor work time instead of earlier outdoor activities in farming etc. The steeply increasing lung cancer rates over the past decades as well as the various oddities affecting the relationship between smoking and lung cancer, e.g. the urban-rural difference in lung cancer risk, also after standardization for smoking, the influence of immigration on lung cancer morbidity as well as the varying rates over the world and other observations, would obtain simple explanations by taking radon daughter exposure into account in addition to smoking. Then, also some curious and hitherto unexplained "inverse" relationships between lung cancer and inhalation of cigarette smoke or bronchitis in air-polluted areas, respectively, would become understandable.