The U.S. Environmental Protection Agency's assessment of risks from indoor radon.

The U.S. Environmental Protection Agency has updated its assessment of health risks from indoor radon, which has been determined to be the second leading cause of lung cancer after cigarette smoking. This risk assessment is based primarily on results from a recent study of radon health effects (BEIR VI) by the National Academy of Sciences. In BEIR VI, the National Academy of Sciences fit empirical risk models to data from 11 cohorts of miners, and estimated that each year about 20,000 lung cancer deaths in the U.S. are radon related. A summary, abstracted from the technical report, is given of the EPA's risk assessment results and methods, including some modifications and extensions to the approach used in BEIR VI. Results include numerical estimates of lung cancer deaths per unit exposure, which had not been provided in BEIR VI.

Statistical issues in biological radiation dosimetry for risk assessment using stable chromosome aberrations.

Biological dosimeters are useful for epidemiologic risk assessment in populations exposed to catastrophic nuclear events and as a means of validating physical dosimetry in radiation workers. Application requires knowledge of the magnitude of uncertainty in the biological dose estimates and an understanding of potential statistical pitfalls arising from their use. This paper describes the statistical aspects of biological dosimetry in general and presents a detailed analysis in the specific case of dosimetry for risk assessment using stable chromosome aberration frequency. Biological dose estimates may be obtained from a dose-response curve, but negative estimates can result and adjustment must be made for regression bias due to imprecise estimation when the estimates are used in regression analyses. Posterior-mean estimates, derived as the mean of the distribution of true doses compatible with a given value of the biological endpoint, have several desirable properties: they are nonnegative, less sensitive to extreme skewness in the true dose distribution, and implicitly adjusted to avoid regression bias. The methods necessitate approximating the true-dose distribution in the population in which biological dosimetry is being applied, which calls for careful consideration of this distribution through other information. An important question addressed here is to what extent the methods are robust to misspecification of this distribution, because in many applications of biological dosimetry it cannot be characterized well. The findings suggest that dosimetry based solely on stable chromosome aberration frequency may be useful for population-based risk assessment.

Mutant frequency at the HPRT locus in peripheral blood T-lymphocytes of atomic bomb survivors.

The mutant frequency at the hypoxanthine-guanine phosphoribosyltransferase locus in peripheral blood lymphocytes was measured for 254 atomic bomb survivors (171 exposed and 83 control survivors) by a colony assay using recombinant human interleukin-2. Weak but significant effects were detected for atomic bomb radiation dose and smoking status at the time of examination but not for age and sex. However, the slope of the dose-response curve is quite small, and the smoking effect would not have been significant without the inclusion of data from just three individuals with extremely high mutant frequencies. The weakness of the dose response is at least partly due to the time lapse of 50 years since radiation exposure. Among the 254 survivors, 23 had chromosome aberration data in lymphocytes and the dose response was highly significant. However, the correlation between the mutant frequency and the proportion of cells with aberrations was not significant. It was concluded that the lymphocyte mutation assay is presently not sensitive enough for biological dosimetry of radiation exposure in the survivors.

Frequency of reciprocal translocations and dicentrics induced in human blood lymphocytes by X-irradiation as determined by fluorescence in situ hybridization.

This study was designed to test the scoring efficiency of reciprocal translocations and dicentrics induced by X-irradiation in vitro using the fluorescence in situ hybridization (FISH) technique. An excess was found in the frequencies of reciprocal translocations relative to those of dicentrics by measurement with FISH at the first cell division after irradiation (translocation:dicentric approximately 60:40). However, when the same metaphases were also evaluated sequentially by a conventional staining method, the ratio of about 50:50 was restored. This was due in part to misclassification of certain dicentrics as reciprocal translocations by the FISH technique.