Strontium-90 and caesium-137 contents in human teeth

Radioactivity and radionuclides in deciduous teeth formed before the Fukushima-Daiichi Nuclear Power Plant accident

The Fukushima-Daiichi Nuclear Power Plant (FNPP) accident in March of 2011 released substantial amounts of radionuclides into the environment. We collected 4,957 deciduous teeth formed in children before the Fukushima accident to obtain precise control data for teeth formed after the accident. Radioactivity was measured using imaging plates (IP) and epidemiologically assessed using multivariate regression analysis. Additionally, we measured 90Sr, 137Cs, and natural radionuclides which might be present in teeth. Epidemiological studies of IP showed that the amount of radioactivity in teeth from Fukushima prefecture was similar to that from reference prefectures. We found that artificial radionuclides of 90Sr and 137Cs, which were believed to have originated from past nuclear disasters, and natural radionuclides including 40 K and daughter nuclides in the 238U and 232Th series contributed to the generation of radioactivity in teeth. We also found no evidence to suggest that radionuclides originating from the FNPP accident significantly contaminated pre-existing teeth. This is the first large-scale investigation of radioactivity and radionuclides in teeth. The present findings will be indispensable for future studies of teeth formed after the FNPP accident, which will fall out over the next several years and might be more contaminated with radionuclides.

An assessment of strontium sorption onto bentonite buffer material in waste repository

In the present study, changes occurring in sorption characteristics of a representative bentonite (WIn-BT) exposed to SrCl₂ (0.001-0.1 M) under the pH range of 1-13 were investigated. Such interaction revealed a significant variation in surface charge density and binding energy of ions with respect to bentonite, and alteration in their physicochemical properties viz., specific surface area, cation exchange capacity, thermal and mechanical behaviour were observed. The distribution coefficients (k _d) calculated for sorption onto virgin (UCBT) and contaminated bentonite (CBT) indicated a greater influence of mineralogical changes occurred with variance of pH and strontium concentration. Notably, the sorption mechanism clearly elucidates the effect of structural negative charge and existence of anionic metal species onto CBT, and depicted the reason behind significant k _d values at highly acidic and alkaline pH. The maximum k _d of UCBT and CBT_{(0.001M SrCl2)} were 8.99 and 2.92 L/kg, respectively, at the soil pH 8.5; whereas it was 2.37 and 1.23 L/kg at pH 1 for the CBT_{(0.1M SrCl2)} and CBT_{(0.01M SrCl2)}, respectively. The findings of this study can be useful to identify the physicochemical parameters of candidate buffer material and sorption reversibility in waste repository.

Strontium-90 concentration measurements in human bones and teeth in Greece

Strontium-90 concentration was measured in human bones and teeth collected in Greece during the period 1992-1996. One hundred and five bone samples, mainly cancellous bone, and 108 samples, taken from a total of 896 individual teeth were processed. Samples were classified according to the age and sex of the donors. Samples were chemically pre-treated according to a specially devised method to enable extraction of 90Y, at equilibrium with 90Sr in the original sample. Subsequently, 90Y beta activity was measured with a gas proportional counter. Radiostrontium concentration in bone samples showed small variations with respect to age or sex, with an average value of 30 mBq 90Sr/g Ca. However, 90Sr concentration measurements in teeth demonstrated a pronounced structure, which clearly reflects contamination from the 1960s atmospheric nuclear weapons tests and the more recent Chernobyl accident. This difference is attributed to the different histological structure of skeletal bones and teeth, the later consisting mainly of compact bone. An age-dependent model for radiostrontium concentration in human bones and teeth is developed which is able to successfully reproduce the experimental data. Through a fitting process, the model also yielded calcium turnover rates for compact bone, as a function of age, as well as an estimate of radiostrontium contamination of foodstuffs in Greece for the past four decades. The results obtained in this study indicate that radiostrontium environmental contamination which resulted from the atmospheric nuclear weapons tests in the 1960s, exceed by far that caused by the Chernobyl accident.

Strontium-90 concentrations in human teeth in south Ukraine, 5 years after the Chernobyl accident

Approximately 1000 human teeth, collected in South Ukraine, in 1990-1991, were measured for 90Sr concentration. The teeth were grouped into 18 samples according to the age and sex of the donors. Measured levels of 90Sr concentrations were lower by a factor of 10 than measurements taken in the mid-1960s and mid-1970s. An interesting feature of the data is a 3-fold enhancement of contamination levels in the 25-45 year-old age group of the male population. A possible explanation for this anomaly is that this age group contains a significant number of men who were mobilized immediately after the Chernobyl accident for clean-up operations within the 30-km zone around the damaged nuclear power plant.