Skip to main content

Currently Skimming:

1 Introduction
Pages 20-35

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 20...
... . That hypothesis was not uniformly accepted until the findings of epidemiologic studies of other groups of radon-exposed underground miners were reported during the 1950s and 1960s (see Lorenz 1944 for an early view of the evidence and Proctor 1995 for a review of the controversy; NRC 1988 summarizes the epidemiologic evidence)
From page 21...
... 218 it.~. 214 210 206 21 The short-lived radon progeny 0.019% ASTATINE RADON 2S 0 035S la la l T 0.21% ~ a | THALLIUM | r LEAD | | BISMUTH | IPOLONIUM| ~:~h~ 0 000002% 0 00013% a a a I JER8CmURY GALLIUM ~ FIGURE 1-1 The radon-decay chain.
From page 22...
... Initially, research was driven by the need to characterize the risks faced by underground miners so that exposure limits that would keep risks to an acceptable level could be set. The work emphasized epidemiologic studies of the uranium and other underground miners exposed to radon, but animal studies were also conducted to address the modifying effects of such factors as the presence of ore dust and diesel exhaust, cigarette-smoking, and dose rate.
From page 23...
... , which are much lower than the exposures of most of the miners included in the epidemiologic studies. The degree of uncertainty in the risk estimates increases from the high end of the exposure range where risks are
From page 24...
... The extrapolation requires assumptions about the relationship between exposure to radon and lung-cancer risk and a careful exploration of the comparative doses from alpha particles delivered to the lung in the mining and indoor environments. The extrapolation also requires assumptions on the potential modifying effects of cigarette-smoking, age at exposure, and sex.
From page 25...
... The BEIR IV committee analyzed data from 4 cohorts of underground miners, using regression methods to develop a model that described the relationship between excess relative risk and exposure to radon progeny during 3 temporal periods of time since exposure. The model also incorporated an age dependence of the effect of radon on lung-cancer risk.
From page 26...
... In addition to the previously used dosimetric and epidemiologic approaches, statistical models can also be applied that are based on a biologic construct of the effect of radon. The dosimetric approach focuses on computing the doses deposited in lung target cells by alpha particles emitted from radon progeny deposited in various compartments of the lung.
From page 27...
... was rejected due to the many assumptions needed to generate risk estimates for prolonged localized exposure to densely-ionizing radiation, based on risks for acute whole-body exposures to ~ rays. Use of data from studies of residential radon exposure was rejected for the primary risk estimation due to the very limited statistical power available in these studies.
From page 28...
... The multidisciplinary BEIR VI phase 2 committee worked in topic-oriented groups that addressed exposure and dosimetry; molecular and cellular aspects of radon carcinogenesis, including the findings of in vitro approaches and animal studies; epidemiologic studies of miners; case-control studies in the general population; and risk modeling. When the committee began its work, it was recognized that the data on the 11 cohorts of miners would be essential for the development of a new risk model; the committee obtained the cooperation of the principal investigators for the individual cohort studies so that additional analyses of the data could be undertaken to develop a risk model.
From page 29...
... rated from the context set by controversy and debate over the management of the risk posed by indoor radon. In the United States, the EPA has pursued a broad national strategy to reduce radon risks through voluntary testing of homes and mitigation of radon in those with an annual average above 148 Bq~3 (4 pCiL-~.
From page 30...
... · Use biologic dosimetry to reduce the uncertainties associated with the exposure-dose relationship and apply the reduced uncertainties in various aspects of lung dosimetry to risk calculations. Studies of Miners · Critique the recently completed analyses of pooled data on 11 cohorts and whatever new risk models emerge from them and use the database to suggest additional analyses.
From page 31...
... is also in this range, as are the action levels set by other countries. The BEIR VI committee therefore characterized the certainty that could be attached to risk estimates made with its model, moving from a high level of confidence in estimates at exposures comparable with those received by the underground miners to a substantially lower degree of confidence in estimates related to typical indoor exposures.
From page 32...
... Extrapolation from Higher to Lower Exposure Rates The underground miners included in the epidemiologic studies typically received their occupational exposures to radon over several years (Lubin and others 1994~. However, exposure to indoor radon takes place across the full lifetime, so exposure rates are generally far lower for the radon exposures received by the general population than for the exposures received by the miners in the epidemiologic studies.
From page 33...
... In particular, the committee considered the implications of identifying population groups at risk for lung cancer generally or for lung cancer caused by radon progeny specifically. Links Between Biologic Evidence and Risk Models The BEIR VI phase 1 committee recognized that key sources of uncertainty listed above as the first 4 critical issues would be best addressed by risk models that directly reflect current biologic understanding directly and are not simply empiric and based on analysis of observational data.
From page 34...
... Even allowing for DNA repair and cellular lethality, such a single alpha-particle traversal is known to produce, with significant probability, largescale damage to the DNA in surviving traversed cells. Thus, at low exposure levels, a further decrease in the exposure would result in a proportionate decrease in the number of target cells traversed by single alpha particles, and thus suffering large scale DNA damage.
From page 35...
... When the risk model is applied to the general population, possible differences between miners and the general population need consideration; that is, similar exposures to radon progeny in homes and miners may not result in the same doses of alpha energy for target cells. Following the approach of the BEIR IV committee, the BEIR VI committee used a mathematical model of the lung to calculate doses to target cells received by miners and by the general population for a given exposure.


This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More information on Chapter Skim is available.