Concentration of 239,240Pu in human autopsy tissues. Preliminary report of a comparative study on different populations

Determination of 240Pu/239Pu isotopic ratios in human tissues collected from areas around the Semipalatinsk Nuclear Test Site by sector-field high resolution ICP-MS

Information on the 240Pu/239Pu isotope ratios in human tissues for people living around the Semipalatinsk Nuclear Test Site (SNTS) was deduced from 9 sets of soft tissues and bones, and 23 other bone samples obtained by autopsy. Plutonium was radiochemically separated and purified, and plutonium isotopes (239Pu and 240Pu) were determined by sector-field high resolution inductively coupled plasma-mass spectrometry. For most of the tissue samples from the former nine subjects, low 240Pu/239Pu isotope ratios were determined: bone, 0.125 +/- 0.018 (0.113-0.145, n = 4); lungs, 0.063 +/- 0.010 (0.051-0.078, n = 5); and liver, 0.148 +/- 0.026 (0.104-0.189, n = 9). Only 239Pu was detected in the kidney samples; the amount of 240Pu was too small to be measured, probably due to the small size of samples analyzed. The mean 240Pu/239Pu isotope ratio for bone samples from the latter 23 subjects was 0.152 +/- 0.034, ranging from 0.088 to 0.207. A significant difference (a two-tailed Student's t test; 95% significant level, alpha = 0.05) between mean 240Pu/239Pu isotope ratios for the tissue samples and for the global fallout value (0.178 +/- 0.014) indicated that weapons-grade plutonium from the atomic bombs has been incorporated into the human tissues, especially lungs, in the residents living around the SNTS. The present 239,240Pu concentrations in bone, lung, and liver samples were, however, not much different from ranges found for human tissues from other countries that were due solely to global fallout during the 1970's-1980's.

Plutonium in Colorado residents: results of autopsy bone samples collected during 1975-1979

Concentrations of (239,240)Pu and the 240Pu/239Pu atom ratios were measured in rib samples from 55 non-occupationally exposed Colorado residents. Samples were collected at autopsy during 1975-1979 under an earlier study intended to compare plutonium levels in liver and lung of people who lived at various proximities to the Rocky Flats Environmental Technology Site (RFETS) near Denver. Overall, median (239,240)Pu concentrations from rib samples were 100, 80, and 57 microBq g(-1) ash weight for area locations A, B, and C, respectively. Area A encompassed subjects who lived within 25 km of RFETS, area B was between 25 and 50 km from RFETS, and area C included all of Colorado outside 50 km from the site and east of the continental divide. The corresponding median plutonium skeletal burdens estimated for these area locations were 146, 93, and 71 mBq, respectively. A statistically significant difference was noted only between plutonium concentrations in male rib samples and their skeletal burdens from area A compared to area C. However, based on a regression analysis of all study subjects, distance from RFETS was not statistically correlated to plutonium rib concentrations or skeletal burdens in this sample. Overall, median 240Pu/239Pu atom ratios were 0.20, 0.18, and 0.17 for areas A, B, and C, respectively. Although higher (239,240)Pu concentrations and skeletal burdens were indicated in area A males than area C males, we cannot conclude that RFETS releases may have caused this difference. The decreasing trends in the 240Pu/239Pu ratios with distance from RFETS are contrary with such a conclusion and strongly indicate that the material was primarily global fallout rather than weapons-grade plutonium that was processed at RFETS. Furthermore, there are other plausible explanations for the differences observed between area A and C residents. These include a decreasing trend in global fallout from the Rocky Mountain foothills eastward, smoking history differences, sample selection criteria, and possibly other unidentified factors. Nevertheless, estimated levels of total plutonium in this sample of Colorado residents were low and within the range of reported literature values for general, world-wide populations.

Environmental plutonium in humans

Although the current world inventory of plutonium is overwhelmingly man-made, it is important to recognize that 244Pu was a primeval radioelement and that 239Pu is formed continuously by spontaneous fission of 238U; the atom ratio U:Pu being about 10(11):1. It has been calculated that the human body has always carried a base load of, perhaps 10(3)-10(5) atoms (< 0.2 amol) of natural plutonium. Since 1945, the release of 239Pu into the environment from atmospheric nuclear weapons testing has added to this base load a civilization-related load which, at approximately 300 fmol, is at least 5 orders of magnitude greater. Within the human body plutonium is deposited mainly in the liver and skeleton where it appears to be retained tenaciously with half-times of many years. Based on 1970-1980 levels, environmental plutonium may give rise to alpha-particle radiation doses of approximately 3-7 microSv/a in human bone and approximately 10-20 microSv/a in liver, doses which from our present understanding of the radio-and chemical toxicity of plutonium are far too small to cause any recognizable health effects.