Health Risks of Radon and Other Internally Deposited Alpha-Emitters BEIR IV (1988) / Chapter Skim
Currently Skimming:
III The Effects of Radon Progeny on Laboratory Animals
III The Effects of Radon Progeny on Laboratory Animals
Pages 430-444
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 430... ...
INHALATION STUDIES AT THE UNIVERSITY OF ROCHESTER Beginning in the 1950s, investigators examined the biological and physical behaviors of radon daughters and the dosimetry of radon daughters in the respiratory tract.~20~25 Shapiro3i exposed rats and dogs to radon alone at several concentrations and to radon with radon daughters attached to room-dust aerosols. The degree of attachment of radon daughters to carrier dust particles was shown to be an important determinant of the alpha-radiation dose to the airway epithelium and that more than 95%0 of the dose to the airway epithelium was due to the short-lived radon daughters radium A (hippo)
|
From page 431... ...
INHALATION STUDIES AT COGEMA The studies by Chameaud and colleagues2~8 were begun in the late 1960s and early 1970s to determine whether radon and its daughters induced tumors in rats and to provide experimental data to support the epidemiological data on radon-daughter carcinogenesis. Before 1972, rats were exposed to ambient air that was enriched with radon after passage through trays of finely ground ore containing 25% uranium.
|
From page 432... ...
In two major experiments,2 rate were exposed by inhalation to stable cerium hydroxide or to uranium-ore dust concentrations with and without radon daughters, at 130 mg/m3, to determine whether the presence of dust altered the carcinogenic effect of radon daughters. Exposure to stable cerium hydroxide before exposure to radon daughters shortened the induction latent period by 2-3 months.
|
From page 433... ...
Later experiments, which confirmed these pathological findings, extended the radon-daughter exposures to approximately 20-50 WLM.5 7~8 Tumor-incidence and survival-time data and lifetime lung-tumor risk coefficients are shown in Table III-1. Although the risk data are uncorrected for life-span shortening, hazard-function analysis demonstrated that when the data are adjusted for competing causes of death, the excess risk of developing pulmonary tumors is approximately linearly related to exposure throughout the range of exposures studied.~9 Further findings are given below.
|
From page 434... ...
434 ._ so o Ct U, ._ EM C~ ._ En Ct ._ Cal o ~ so - i =, ._ ~ sol o ~ ~ o He o << V, V o _ ~ _ ~ ~ ·C)
|
From page 435... ...
The investigators have not reported whether the latent period for cancer was influenced by smoke exposure; the observation that tumors in the radon-daughterand smoke-exposed anneals were larger and more invasive than those in animals exposed only to radon daughters might be indicative of a shorter latent period for smoking-related tumors. The COGEMA studies have produced more than 800 lung cancers in about 10,000 rats exposed to radon daughters with ambient aerosols and in mixtures with other pollutants.
|
From page 436... ...
The mean radon-daughter exposure in the hamster experiments was about 10,000 WLM. Lifetime exposures of beagles to mixtures of radon daughters, uranium-ore dust, and cigarette smoke caused significant life-span shortening compared with that of controls.
|
From page 437... ...
The lung cancers were about 70% bronchogenic carcinomas and 30% bronchioloalveolar carcinomas.~5 The sunplified convention used was that squamous cell carcinomas and mucus-staining adenocarcinomas were bronchogenic carcinomas and that tumors of Clara cell or type II alveolar cell origin and non-mucus-staining adenocarcinomas were bronchioloalveolar carcinomas. Lifetime inhalation exposures of hamsters produced severe radiation pneumonitm but only four squamous cell carcinomas (three in the radon daughter~only group and one in the group exposed to radon daughters and uranium-ore dust)
|
From page 438... ...
with decreasing radondaughter exposure rate, increasing unattached fraction of radon daughters, and increasing radon-daughter disequilibrium. The lung cancers induced after exposures of approximately 300 5,000 WLM were about 70% bronchogenic carcinomas and 30% bronchioloalveolar carcinomas.
|
From page 439... ...
In the COGEMA rat experiments, cigarette smoke was cocarcinogenic with radon daughters if exposure to smoke followed completion of exposure to the radon daughters,4 but not if smoking preceded the radon-daughter exposures. In the PNL dog experiments, lung-tumor incidence decreased when animals were exposed to radon daughters and cigarette smoke alternately on the same day.
|
From page 440... ...
are probably due to the lower average exposure rates of the PNL experiments. The uncertainties in the PNL lung-cancer incidence and risk-coefficient data are considered to be due mainly to uncertainties in the exposure data (standard deviations were generally well within +20% of the means)
|
From page 441... ...
Kushneva23 reported that rats given 50 me of silica by instillation with inhalation exposures to radon at 8 psi/liter developed many more pulmonary effects, including both adenomas and carcinomas, than did anneals exposed to silica alone; the number of tumors and control animals was small. When silica dusts were included in the exposures, the radondaughter inhalation studies at COGEMA and PNL showed no increased tumorigenic efficiency over exposures to radon daughters alone if these exposures exceeded a few hundred WLM.
|
From page 442... ...
. Decreases if smoking alternates on same day with radon-daughter exposures Radon-daughter cumulative exposure Radon-daughter exposure rate Radon-daughter unattached fraction Radon-daughter disequilibrium Concomitant exposure to cigarette smoke Increases if smoking follows cumulative radondaughter exposures No effect if smoking precedes cumulative radondaughter exposures Large-scale anneal studies may become useful for elucidating the ~nteractions between radon daughters and other inhaled pollutants.
|
From page 443... ...
1982. Influence of radon daughter exposure rate and uranium ore dust concentration on occurrence of lung tumors.
|
From page 444... ...
1984. Influence of radon daughter exposure rate, unattachment fraction, and disequilibrium on occurrence of lung tumors.
|
Key Terms
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.