Postprandial changes in the exhalation rate of radon produced in vivo.

The rate of exhalation of radon by persons with long-standing radium burdens increases about twofold shortly after a meal. The increase is short-lived and "normal" values are regained in 1.5 to 2 hours. The effect may account in part for the poor reproducibility in estimates of the freely emanating part of the radium content.

Radioactivity measurements of former military personnel exposed to weapon debris.

Sixteen former military personnel who were present at the "Smoky" atmospheric nuclear weapon test have been investigated for internal deposits of radioactivity. Whole-body and thorax gamma-ray measurements, thorax and skeletal actinide measurements, and urinalyses for plutonium-239 and strontium-90 indicated no evidence of radioactivity in excess of that found in the general population.

Postmenopausal loss of Ra acquired in adolescence or young adulthood: quantitative relationship to radiation-induced skeletal damage and dosimetric implications.

From the results of serial measurements of body 226Ra activity in 13 former luminous dial workers 30-60 y after relatively brief periods of intake of luminous compounds in adolescence or young adulthood, we determined the postmenopausal rate of elimination of Ra in percent of contemporary body Ra content per year. This rate was negatively correlated with the "reduced x-ray score," a measure of radiation osteonecrosis observed radiographically in the 13 subjects (r = -0.85, P less than 0.001). The clearance rates of subjects retaining low Ra activity were greater than predicted by retention models. We conclude that for those members of the Ra-exposed population under study for health effects at our institution who sustained the lesser degrees of macroscopic skeletal damage, present estimates of skeletal absorbed dose are systematically low, by at most a factor of 2.

Measurement techniques for radium and the actinides in man at the Center for Human Radiobiology.

Various techniques are employed to determine the amounts, retention, and distribution of radioactivity in human subjects in vivo. The principal method is gamma-ray spectrometry with large NaI(Tl) scintillation crystals ("whole-body counting"). The geometries used include an arc of 1.5-m radius in which all parts of the body are roughly equidistant from the detector, a reclining chair and a flat bed with detectors placed above and below the subject. When a sufficient amount of radioactivity is present in a subject, scanning techniques assist in determining its distribution in the body. Specialized instruments such as a xenon-filled proportional counter and a dual-crystal (phoswich) detector are used to measure low-energy photon emitters, primarily plutonium and americium. americium. There are three primary methods of calibrating the detectors. The first is analytical, in which a rigorous mathematical treatment is employed; the second involves the administration of tracer amounts of radioactivity to human volunteers; the third consists of determining detector response to known amounts of radioactivity in a phantom. All three methods can be intercompared, and further evaluated by comparing the results of measurements in vivo with those of postmortem analyses. For both radium and thorium cases measured in vivo, the interpretation of the results is complicated by the fact that neither radium nor thorium emit gamma rays of any consequence. Instead, the observed gamma rays result from the decay of 214Bi (RaC) and 208Tl (ThC"), respectively. Since each of these nuclides is preceded in the decay chain by an isotope of the noble gas radon, some of which is exhaled, its activity is not equal to that of the parent radium or thorium. Therefore, breath samples are collected to determine the exhalation rate of the precursor isotope, 222Rn (radon) or 220Rn (thoron). The total body content is then the sum of the gamma activity and the exhaled radioactivity, referred to as the retained and emanating fractions, respectively.

Distribution and retention in bone of 226Ra and comparison with the ICRP 20 model.

Analyses are presented of the ratios of 226Ra to calcium in over 650 samples of compact and cancellous bone from 66 female and 26 male subjects who had died from less than 1 to 60 yr after first exposure to radium. The 226Ra/Ca ratios were normalized to the terminal 226Ra skeletal content. The 226Ra/Ca ratios for vertebrae were essentially identical to those for other cancellous bone for a given subject. Comparisons of the data with predictions of the ICRP model of alkaline earth metabolism show that for female cancellous bone the normalized 226Ra/Ca ratios tended to be greater than predicted, while those for female cortical bone (femoral and tibial shaft) tended to be less. The data for males were fitted better by the model. A modification of the model to reduce the amount of radium deposited in soft tissue fitted the data better in some respects. A straight line linear least squares fit to the data appeared to fit as well as, or better than, the models. A radiation effect was suggested in that the normalized 226Ra/Ca ratio for vertebrae relative to the ratio expected increased with skeletal absorbed dose for vertebrae. However, no such effect was apparent for compact bone or for the cancellous bone as a whole.

Leukaemia incidence in the U.S. dial workers.

Late biological effects of radium deposited in the human skeleton have manifested themselves unequivocally as osteogenic sarcomas or carcinomas of the mastoid air cells or paranasal sinuses. On the basis of current estimated risk factors, it might be expected that an excess of certain other malignancies could occur in a population of the size of the group exposed to radium (some 3500 cases located, which more than 2000 have measured 226Ra and 228Ra burdens), compared with the incidence in the population at large. An increased incidence of breast cancer has already been reported in female dial workers and it was related to the initial radium intake. On the other hand, very little information is available on the induction of leukaemia by alpha-radiation in human bone marrow. This paper therefore reports an investigation of the incidence of leukaemia among the radium workers. This covers a very wide range of radium burdens and has been done in the light of reasonable estimates of the mean alpha-particle dose received by the skeletal haemopoietic marrow. The number of leukaemia cases is identified and compared with (a) the expected number in a comparable population of the same size and age distribution and (b) predictions based on the risk factor proposed for protection purposes by the ICRP and on the estimated bone marrow doses.

Metabolism of Ca and Sr in late adult life.

Data are presented on the metabolism of Ca and Sr in a healthy male volunteer who, in a series of investigations conducted between the ages of 53 and 82 y, received controlled intakes of 45Ca, 47Ca, or 85Sr. No age-related trends were established, either in factors affecting the skeletal deposition of the tracers or in their subsequent retention studied for up to 462 d after intake. The data thus lend support to an important working postulate in the ICRP's model of alkaline earth metabolism.

Metabolism of ingested U and Ra.

The literature on metabolism of U and Ra for man relevant to deriving drinking water standards has been reviewed and summarized. Radium is well understood, but significant gaps remain in our knowledge about U metabolism. Limits should be based on an equilibrium model where a constant relationship between intake and organ burden is established, using the best and most likely metabolic parameters. For the skeleton we conclude that the best estimate of skeletal burden expressed in days equivalent intake are 25 days for 226Ra, 10 days for 228Ra, and 0.3 days for 224Ra. For long-lived isotopes of U, we chose 11 days, with a range between 1 and 35 days. The committee believes that intake of natural U in water should be limited by considerations of toxicity to the kidney, and we believe that the metabolic model of Spoor and Hursh with a modified gastrointestinal (GI) absorption (1.4%) should be used to infer kidney content. Our review and analysis of the world literature leads us to believe the average human GI absorption of U is most likely 1-2% and is probably reasonably independent of age or the mass of U ingested. Using a safety factor of 50-150, the committee recommends a limit of U in water of 100 micrograms/l in order to limit toxic effects in the kidney. One hundred micrograms/liter is equivalent to 67 pCi/l of long-lived alpha-emitting natural U isotopes. Further research into the distribution of U in the human body is desirable, especially at natural levels in kidney and skeleton, the time-dependent pharmacokinetics of U in animals, the GI absorption of U in man from water and food, toxicological and U distribution studies in animals under conditions of chronic oral U intake, and metabolic model error propagation.