Thorium isotopes in autopsy samples from thorium workers.

Concentrations of 232Th and activity ratios of 228Th to 232Th and 230Th to 232Th were determined in autopsy samples from five former employees of a thorium refinery. The ranges of 232Th activity concentrations (mBq per gram of wet tissue) were 0.17-94 in lungs, 3.9-1210 in pulmonary lymph nodes, 0.14-1.19 in bones, 0.015-0.68 in liver, 0.97-5.8 in spleen, and 0.009-0.068 in kidneys. These concentrations are 10 to 1,000 times greater than have been reported for persons not occupationally exposed to thorium. In most of the samples, the ratios of 228Th to 232Th and 230Th to 232Th activity at death of the subject were 0.2-0.4 and 0.1-0.2, respectively. 228Th to 228Ra activity ratios (+/- standard errors) of 0.86 +/- 0.11 in lungs and 1.18 +/- 0.13 in lymph nodes of one subject were obtained by calculation from ratios of 228Th to 232Th.

Louisiana Tumor Registry: new developments and activities.

New developments in the Louisiana Tumor Registry (LTR) over the past 3 years have enhanced the operation of the LTR and broadened its functions. Recent funding for numerous special studies and research collaborations have expanded the registry activities from data collection and special etiologic studies to more completely address the mandates of registry law, which require the LTR to participate in studies of cancer causes, treatment, and survival in order to reduce cancer morbidity and mortality in Louisiana.

Highlights of cancer incidence in Louisiana, 1988-1992.

This paper highlights the major findings from the recently released volume of the Louisiana Tumor Registry monograph series: Cancer Incidence in Louisiana, 1988-1992. One out of three Louisiana residents will develop cancer in his or her lifetime. Lung cancer remains the most common cancer for all races, both genders combined. Lung cancer rates for women continue to rise substantially (20% over the previous 5-year period) and African-American men in the Acadiana Region have the state's highest lung cancer rate. The number of prostate cancer cases has surpassed that of lung cancer for the first time in Louisiana men; the sizable increase since 1983 (about 50%) in prostate cancer likely reflects the recent aggressive screening by the PSA test. Breast cancer remains the most common cancer among Louisiana women and incidence rates have increased about 20% over the previous 5-year period. Geographic comparisons show that the New Orleans Region continues to have rates higher than state averages, and a clear pattern of high cancer risk has emerged for the Acadiana region. The Central Louisiana and the Baton Rouge Regions have rates lower than state averages.

Radium-226 dose to a boy from playing on mill tailings.

Two boys born in September 1949 played on uranium mill tailings from about ages 8 to 12. One of these boys was diagnosed as having leukemia at age 15.5. The 226Ra body burden of the survivor was measured at age 38. The whole-body 226Ra content measured by counting in vivo was 0 +/- 17 Bq and independently by Rn breath analysis as 4.3 +/- 2.1 Bq. At the same time, a control subject with no known exposure to 226Ra, matched in age, height, and weight, was also measured. The whole-body content was estimated as 4 +/- 15 Bq and independently by Rn breath analysis as 5.5 +/- 3.7 Bq. The body burden of the control subject was not significantly different from that of the exposed person. The radiation dose to the marrow-free skeleton assuming a constant 226Ra:Ca ratio since birth was 0.49 and 1.33 mGy at ages 14 and 38, respectively. The radiation dose to the marrow-free skeleton assuming 226Ra intake only between ages 8 to 12 was 1.4 and 2.8 mGy at ages 14 and 38, respectively. The best estimate is the mean of these two estimates: 0.9 and 2.1 mGy at ages 14 and 38, respectively. The alpha-particle dose to the red marrow from 226Ra and its decay products was 0.05 mGy at age 14 and 0.10 mGy at age 38. Since no excess was found for the radium dial painters whose doses were much higher, the induction of leukemia by doses of this magnitude would seem quite unlikely.

Radium-226 whole-body gamma counting and 222Rn breath analysis: report on a subject exposed to uranium mill tailings.

One of two boys born in September 1949 who played on U mill tailings between age 8 and 12 was diagnosed as having leukemia at age 15.5. The exposed and control subjects were well matched; they were approximately the same age and both were 1.85 m (6' 1") in height and weighed 75.2 kg (165 pounds). The result obtained by gamma spectrometric method for the exposed subject was 0 +/- 17 Bq (0 +/- 470 pCi), while that for the control subject was 4 +/- 15 Bq (100 +/- 400 pCi). The result obtained by the Rn breath method for the exposed subject was 4.4 +/- 0.7 Bq (120 +/- 20 pCi), while that for the control was 5.4 +/- 1.4 Bq (150 +/- 38 pCi). These results suggest that the 226Ra body burden of the exposed subject is within the range of those observed in subjects exposed only through normal food sources, which have a mean 226Ra content of 1.5 Bq (range: 0.4-4.4 Bq) so that no significant mill-tailing intake is indicated. The best estimate of alpha particle dose to the red marrow from 226Ra and its decay products was 0.05 mGy at age 14 and 0.10 mGy at age 38. This dose, when compared to that observed in the dial painters, suggests that the leukemia was not caused by uptake of Ra from the mill tailings.

Calcium-41 concentration in terrestrial materials: prospects for dating of pleistocene samples.

Calcium-41 has been suggested as a new tool for radiometric dating in the range of 10(5) to 10(6) years. The concentration of cosmogenic calcium-41 in natural samples of terrestrial origin has now been determined by high-sensitivity accelerator mass spectrometry after pre-enrichment in calcium-41 with an isotope separator. Ratios of calcium-41 to total calcium between 2 x 10(-14) and 3 x 10(-15) were measured for samples of contemporary bovine bone and from limestone deposits. Some prospects for the use of calcium-41 for dating Middle and Late Pleistocene bone and for other geophysical applications are discussed.

The estimation and potential radiobiological significance of the intake of 228Ra by early Ra dial workers in Illinois.

We made radiochemical determinations of 226Ra and the 228Ra-decay product, 228Th, in samples of bone from former Ra dial workers who belonged to a major cohort of Ra-exposed persons under study for health effects at our institution. Most of the former workers were long-term residents of two communities supplied with drinking water containing elevated natural levels of 228Ra and 226Ra, so determinations also were made of radioactivity in samples of bone from long-term residents not occupationally exposed to Ra. The 228Th activity of the bones of the former workers, after correction for the presence of natural radioactivity, showed that some had significant occupational intakes of 228Ra, contrary to published reports that 228Ra was never used by the Illinois company that had employed the cohort of early workers. For 14 workers hired in the years 1920-23, the calculated ratio of the occupational intake of 228Ra to 226Ra activity averaged 0.15 (coefficient of variation 0.65), whereas for three workers hired in 1924, it was not significantly different from zero (mean 0.05, coefficient of variation 1.5). The risk of radiogenic cancer for the typical worker hired before 1924 may have been nearly twice that incurred in the absence of the 228Ra component of the Ra intakes.

Mortality from cancers of major sites in female radium dial workers.

The female radium dial workers have now experienced significant mortality from cancers other than the bone sarcomas and head carcinomas long known to be radium induced. The relationships of radium exposure to mortality from cancers of the stomach, pancreas, colon, rectum, liver, lung, breast, cervix, and corpus uteri, and from leukemia were studied in 1,285 pre-1930 dial workers. Mortality was compared with that expected from rates for US white females, with and without adjustment for local area mortality rates, and with mortality in dial workers exposed from 1930 to 1949. For the 693 cases whose body content of radium has been measured since 1955, dose-response relationships of cancer to systemic intake of radium and duration of employment were examined. Liver, pancreatic, cervical, and uterine cancers were clearly unrelated to radium exposure. Other cancers of the digestive tract appeared to be indirectly, if at all, associated with work in radium facilities. Lung cancer requires further investigation; inhalation exposures of the dial workers were reviewed. Analyses of the breast cancer data uncovered several observations inconsistent with the previously suggested causal association with radium exposure. Multiple myeloma was also reviewed. A threefold excess risk of death due to multiple myeloma has occurred, but is more closely correlated with duration of employment (a surrogate for external gamma radiation) than with radium intake.

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.

Dose-response relationships for radium-induced bone sarcomas.

The incidence of bone sarcomas among 3055 female radium-dial workers who entered the dial industry before 1950 was used to determine dose-response relationships for the induction of bone sarcomas by radium. Two subpopulations were analyzed: all measured cases who survived at least 5 yr after the start of employment and all cases who survived at least 2 yr after first measurement. The first constituted a group based on year of entry; it contained 1468 women who experienced 42 bone sarcomas; the expected number was 0.4. The second comprised a group based on first measurement; it contained 1257 women who experienced 13 bone sarcomas; the expected number was 0.2. The dose-response function, I = (C + alpha D + beta D2)e-gammaD, and simplifications of this general form, were fit to each data set. Incidence (I) was in units of bone sarcomas per person-yr; (D) was the quantity (muCi) of radium that entered the blood. Two functions, I = (C + alpha D + beta D2)e-gammaD and I = (C + beta D2)e-gammaD, fit the data for year of entry (p greater than or equal to 0.05); both these functions and I = (C + alpha D) fit the data for first measurement. The function I = (C + beta D2)e-gammaD was used to predict the number of bone sarcomas in all other pre-1950 radium cases (medical, laboratory and other exposures); fewer were actually observed than the fit of this function to the female dial workers predicted.

Mortality among male workers at a thorium-processing plant.

The long-term health effects of exposure to thorium are of interest because of the possible increased use of thorium as an energy source in reactors using 232Th to produce 233U. Mortality is described in a cohort of 3039 men who were employed between 1940 and 1973 at a company involved in the production of thorium and rare earth chemicals from monazite sand. Based on deaths ascertained by the Social Security Administration and mortality rates for U.S. white males, the standardized mortality ratio (SMR) for all causes was 1.05 with 95% confidence limits (95% CL) of 0.96 and 1.15. Much of the excess mortality was attributable to non-occupational motor vehicle accidents (SMR = 1.64; 95% CL = 1.16 and 2.23), but SMRs were also high for lung cancer (1.44; 95% CL = 0.98 and 2.02), pancreatic cancer (2.01; 95% CL = 0.92 and 3.82), and diseases of the respiratory system (1.31; 95% CL = 0.92 and 1.83). In a subgroup of 592 men who worked for at least one year in selected jobs (indicative of highest exposure to thorium and thoron) that was followed up more intensively, the SMR for pancreatic cancer was significantly elevated (i.e. 4.13; 95% confidence limits = 1.34 and 9.63). The SMR for lung cancer was 1.68 (95% CL = 0.81 and 3.09), while that for respiratory diseases was 1.20 (95% CL = 0.52 and 2.37). Information on smoking habits in a sample of survivors suggested that smoking could have explained at least part of the excess mortality from lung and pancreatic cancer and from diseases of the respiratory system. Continued follow-up of the cohort through morbidity and mortality studies is needed to evaluate further the possible long-term effects of exposure to radioactivity and chemicals in the thorium extraction process.