The impact of the probability of causation on the radiation protection program.

Although the probability of causation approach is the only scientific basis on which a given cancer can be judged to be causally related to a given exposure, the impact of this concept on the radiation safety program could be counter-productive. As health physicists, the practices and the concepts we employ have been developed to protect the worker. Effective dose equivalent and committed dose equivalent are protective concepts but useless for probability of causation analysis. Perhaps extensive records will be the only way that good radiation protection and probability of causation analysis can coexist.

Gastrointestinal absorption of plutonium by the Marshall Islanders.

The gastrointestinal absorption constant (f1) is a critical parameter in assessing systemic uptake following the ingestion of a radioactive material and in monitoring such intakes. This study addresses the latter, particularly for plutonium, and from environmental measurements derives an f1 value of 4 x 10(-4) for the Marshallese population. The uncertainty associated with the methodology and measurements used in this f1 value assessment is evaluated. This evaluation takes into account the results from 24-h urine samples and the particular lifestyle of the Marshallese. Plutonium intake resulting from soil consumption is a primary parameter in this evaluation; for this study, it was assumed to be 500 mg d(-1). The f1 value determined here is consistent with the values in ICRP Publication 67 of 5x10(-4) for ages 1 to adult, and is the same as that suggested by the NRPB.

137Cs exposure in the Marshallese populations: an assessment based on whole-body counting measurements (1989-1994).

The Marshall Islands were the site of numerous tests of nuclear weapons by the United States. From 1946 to 1958, nuclear devices were detonated at Enewetak and Bikini Atolls. Following the inadvertent contamination of the northern islands downwind of the 1954 Bravo Test, Brookhaven National Laboratory became involved in the medical care and the radiological safety of the affected populations. One important technique employed in assessing the internally deposited radionuclides is whole-body counting. To estimate current and future exposures to 137Cs, data from 1989 to 1994 were analyzed and are reported in this paper. During this period, 3,618 measurements were made for the Marshallese. The cesium body contents were assumed to result from a series of chronic intakes. Also, it was assumed that cesium activity in the body reaches a plateau that is maintained over 365 d. We estimated the annual effective dose rate for each population, derived from the recommendations of the International Commission on Radiological Protection. The average 137Cs uptake measured by the whole-body counting method varies from one population to another; it was consistent with measurements of external exposure rate. The analysis, though based on limited data, indicates that there is no statistical support for a seasonal effect on 137Cs uptake. The critical population group for cesium uptake is adult males. Within the 5-y monitoring period, all internal exposures to 137Cs were less than 0.2 mSv y(-1). Similarly, a persistent average cesium effective dose rate of 2 microSv y(-1) was determined for Majuro residents.

Residential radon exposure and lung cancer risk: commentary on Cohen's county-based study.

The large United States county-based study () in which an inverse relationship has been suggested between residential low-dose radon levels and lung cancer mortality has been reviewed. While this study has been used to evaluate the validity of the linear nonthreshold theory, the grouped nature of its data limits the usefulness of this application. Our assessment of the study's approach, including a reanalysis of its data, also indicates that the likelihood of strong, undetected confounding effects by cigarette smoking, coupled with approximations of data values and uncertainties in accuracy of data sources regarding levels of radon exposure and intensity of smoking, compromises the study's analytic power. The most clear data for estimating lung cancer risk from low levels of radon exposure continue to rest with higher-dose studies of miner populations in which projections to zero dose are consistent with estimates arising from most case-control studies regarding residential exposure.

Assessment of plutonium exposure in the Enewetak population by urinalysis.

Since 1980, the inhabitants of Enewetak Atoll have been monitored periodically by scientists from Brookhaven National Laboratory for internally deposited radioactive material. In 1989, the establishment of fission track analysis and of a protocol for shipboard collection of 24-h urine samples significantly improved our ability to assess the internal uptake of plutonium. The purpose of this report is to show the distribution of plutonium concentrations in urine collected in 1989 and 1991, and to assess the associated committed effective doses for the Enewetak population based on a long-term chronic uptake of low-level plutonium. To estimate dose, we derived the plutonium dose-per-unit-uptake coefficients based on the dosimetric system of the International Commission on Radiological Protection. Assuming a continuous uptake, an integrated Jones's plutonium urine excretion function was developed to interpret the Enewetak urine data. The Appendix shows how these values were derived. The committed effective doses were 0.2 mSv, calculated from the 1991 average plutonium content in 69 urine samples.

Assessment of plutonium exposures in Rongelap and Utirik populations by fission track analysis of urine.

A nuclear device, code-named Bravo, detonated at Bikini Atoll at 6:45 a.m. on 1 March 1954, unexpectedly released a large amount of radioactivity. Over 40 years after this incident, the study of its impact on the radiological health and environmental safety of the residents of Rongelap and Utirik Atolls continues. In 1987, researchers at Brookhaven National Laboratory established a fission track analysis (FTA) method for low-level 239Pu urinalysis. Two years later, a new shipboard protocol was developed for collecting 24-h radiologically clean urine samples. The purpose of this paper is to update information on the FTA method for measuring low-levels of plutonium, and to summarize results on the distribution of 239Pu in the populations of Rongelap and Utirik between 1981-1991. Plutonium detection levels (99% confidence level) in these samples were 2-3 microBq, which is equivalent to 0.2-0.3 mSv effective dose equivalent (EDE) to age 70 for Marshallese. The latest 1991 FTA data indicate average EDE of 0.62 mSv and 1.6 mSv for the people of Rongelap and Utirik, respectively, which both are the highest values since 1988.

Quantities and units in radiation protection.

In its Publication No. 60, the International Commission on Radiological Protection (ICRP) introduced a new quantity, the equivalent dose in tissue, HT = sigma R WR DT.R where DT.R is the absorbed dose averaged over the tissue or organ, T, and WR is the radiation weighting factor. The latter depends on the incident radiation, i.e., the type and energy, but is independent of the tissue. On the other hand, a customarily defined quantity, the 'dose equivalent' is maintained (in particular the operational dose-equivalent quantities introduced in ICRU Report 39), but the relationship between the quality factor Q(L) and the linear energy transfer, L, has been redefined. In the case of neutrons, this procedure gives rise to an increase of the corresponding fluence to dose-equivalent conversion factors. The reasons for introducing these and the new tissue-weighting factor changes are discussed.