Two-mutation models for bone cancer due to radium, strontium and plutonium

The detailed analysis of natural radionuclides dissolved in spa waters of the Kłodzko Valley, Sudety Mountains, Poland

A survey was conducted to measure natural radioactivity in spa waters from the Kłodzko Valley. The main goal of this study was to determine the activity concentration of uranium, radium and radon isotopes in the investigated groundwaters. Samples were collected several times from 35 water intakes from 5 spas and 2 mineral water bottling plants. The authors examined whether the increased gamma radiation background, as well as the elevated values of radium and uranium content in reservoir rocks, have a significant impact on the natural radioactivity of these waters. The second objective of this research was to provide information about geochemistry of U, Ra, Rn radionuclides and the radiological and chemical risks incurred by ingestion of isotopes with drinking water. On the basis of results obtained, it is feasible to assess the health hazard posed by ingestion of natural radioactivity with drinking waters. Moreover, the data yielded by this research may be helpful in the process of verification of the application of these waters in balneotherapy. In addition, annual effective radiation doses resulting from the isotopes consumption were calculated on the basis of the evaluated activity concentrations. In dose assessment for uranium and radium isotopes, the authors provided values for different human age groups. The obtained uranium content in the investigated waters was compared with the currently valid regulations concerning the quality of drinking water. Based on the activity concentrations data, the activity isotopic ratios (234)U/(238)U, (226)Ra/(238)U, (222)Rn/(238)U, (222)Rn/(226)Ra and the correlations between radionuclides content were then examined. In brief, it may be concluded on the basis of the obtained results that radon solubility is inversely proportional to radium and uranium dissolution in environmental water circulation. The presented study allows conclusions to be drawn on the radionuclide circulation among different environmental biota: from lithosphere through hydrosphere to biosphere.

EURADOS strategic research agenda: vision for dosimetry of ionising radiation

Since autumn 2012, the European Radiation Dosimetry Group (EURADOS) has been developing its Strategic Research Agenda (SRA), which is intended to contribute to the identification of future research needs in radiation dosimetry in Europe. The present article summarises-based on input from EURADOS Working Groups (WGs) and Voting Members-five visions in dosimetry and defines key issues in dosimetry research that are considered important for the next decades. The five visions include scientific developments required towards (a) updated fundamental dose concepts and quantities, (b) improved radiation risk estimates deduced from epidemiological cohorts, (c) efficient dose assessment for radiological emergencies, (d) integrated personalised dosimetry in medical applications and (e) improved radiation protection of workers and the public. The SRA of EURADOS will be used as a guideline for future activities of the EURADOS WGs. A detailed version of the SRA can be downloaded as a EURADOS report from the EURADOS website (www.eurados.org).

Concerning the health effects of internally deposited radionuclides

The ionizing radiation dose-response relationships for internally deposited radionuclides are examined using data from humans involving Ra and laboratory animal studies involving alpha-emitters Ra, Ra, Ra, Th, Pu, Pu, and Am and beta-emitters Y, Sr, Y, and Ce. Intake routes included ingestion, inhalation, and injection. The lifetime effects are best described by three-dimensional average-dose-rate/time/response surfaces that compete with other causes of death during an individual's lifetime. Using maximum likelihood survival regression methods, the characteristic logarithmic slope for cancer induction was found to be about negative one-third for alpha-emitters or about negative two-thirds for beta-emitters. At the higher average dose-rates the principal deleterious effects were those associated with radiation-induced injury while at intermediate average dose-rates radiation-induced cancer predominates. The relative biological effectiveness for cancer induction of high linear energy transfer alpha radiation with respect to low linear energy transfer beta radiation is a strong function of dose-rate. As average dose-rate decreases, the effectiveness of the beta irradiation drops off more rapidly than that of the alpha irradiation. The cumulative dose yielding a specific level of induced cancer risk is less at lower dose-rates than at higher dose-rates showing an apparent inverse dose-rate effect (up to a factor of about 10 for high linear energy transfer alpha radiation and a factor of about 2 for low linear energy transfer beta radiation). The cumulative radiation dose is neither an accurate nor an appropriate measure of cancer risk associated with protracted ionizing radiation exposure. Cancer risk associated with protracted ionizing radiation exposure is a non-linear function of lifetime average dose-rate to the affected tissues. At low average dose-rates the long latency time required for radiation-induced cancer may exceed the natural lifespan. This long latency results in a lifespan virtual threshold (cancer risk p < 0.001) for each internally deposited radionuclide. For young adult beagles, bone sarcoma induction from alpha-emitting radionuclides was unlikely for cumulative doses below about 1 Gy (20 Sv) delivered specifically to the sensitive tissues at bone surfaces in a manner associated with radionuclide relative potency from highest for Th, Pu, and Pu to lowest for Ra. Bone sarcoma induction from ingested Sr was unlikely for cumulative beta radiation doses below about 20 Gy (20 Sv), but beta irradiation of tissues adjacent to bone also induced leukemia and soft tissue carcinomas above 10 Gy (10 Sv). Inhaled radionuclides tended to be most potent in producing lung carcinoma when the radiation dose was most uniformly distributed in the lung. In young adult beagles lung carcinoma from inhaled alpha-emitting Pu in the dispersible nitrate form was unlikely for cumulative doses below about 0.5 Gy (10 Sv) and below higher cumulative doses for other forms of Pu and Pu depending on relative potency. Lung carcinoma from inhaled beta-emitting Y in relatively insoluble fused aluminosilicate particles was unlikely for cumulative doses below about 5 Gy (5 Sv) and below higher doses for inhaled particles with Y, Ce, or Sr in order of decreasing potency.

Mechanistic models of bone cancer induction by radium and plutonium in animals compared to humans

Two-mutation carcinogenesis models of mice and rats injected with (239)Pu and (226)Ra have been derived extending previous modellings of beagle dogs injected with (239)Pu and (226)Ra and radium dial painters. In all cases statistically significant parameters could be derived fitting data from several research groups jointly. This also lead to similarly parametrised models for (239)Pu and (226)Ra for all species. For each data set not more than five free model parameters were needed to fit the data adequately. From the toxicity ratios of the animal models for (239)Pu and (226)Ra, together with the human model for (226)Ra, an approximate model for the exposure of humans to (239)Pu has been derived. Relative risk calculations with this approximate model are in good agreement with epidemiological findings for the plutonium-exposed Mayak workers. This promising result may indicate new possibilities for estimating risks for humans from animal experiments.

Bone cancer risk in mice exposed to 224Ra: protraction effects from promotion

This paper analyzes data for the osteosarcoma incidence in life-time experiments of (224)Ra injected mice with respect to the importance of initiating and promoting action of ionizing high LET-radiation. This was done with the biologically motivated two step clonal expansion (TSCE) model of tumor induction. Experimentally derived osteosarcoma incidence in 1,194 mice following exposure to (224)Ra with different total radiation doses and different fractionation patterns were analyzed together with incidence data from 1,710 unirradiated control animals. Effects of radiation on the initiating event and on the clonal expansion rate, i.e. on promotion were found to be necessary to explain the observed patterns with this model. The data show a distinct inverse protraction effect at high doses, whereas at lower doses this effect becomes insignificant. Such a behavior is well reproduced in the proposed model: At dose rates above 6 mGy/day a longer exposure produces higher ERR per dose, while for lower rates the reverse is the case. The TSCE model permits the deduction of several kinetic parameters of a postulated two-step bone tumorigenesis process. Mean exposure rates of 0.13 mGy/day are found to double the baseline initiation rate. At rates above 100 mGy/day, the initiation rate decreases. The clonal expansion rate is doubled at 8 mGy/day, and it levels out at rates beyond 100 mGy/day.