A simple method for assessing that internal doses are below action levels.

The accidental or deliberate dispersal of radioactive aerosols into the public environment may require urgent assessments of radiation dose to be made to aid decisions on whether treatment should be implemented, or to reassure the public that doses are acceptably low. However, rapid assessments will be difficult due to lack of information on factors such as the particle size distribution and biokinetic characteristics of the aerosol. A procedure is described that relates the amount of activity of a radionuclide in the body and excreta to time after intake for a specified dose, taking into account the likely variations in aerosol size and differences in the biokinetic behaviour of the same or different chemical forms of the radionuclide. The implementation of the procedure for an intake of caesium-137 and a dose level of 1 mSv is described and the information presented graphically. Figures for other specified dose levels can be produced by simply scaling the data by an appropriate factor. The figures can also be used to assess the most appropriate monitoring procedure and indicate the uncertainty in the assessed dose according to the parameter and parameter values used. This approach is proposed for rapid decisions on public reassurance when potentially large numbers of people are involved. It is not intended as a substitute for individual dose assessment.

Treatment of human contamination with plutonium and americium: would orally administered Ca- or Zn-DTPA be effective?

Accidental or deliberate dispersion of plutonium (Pu) and americium (Am) into the public environment could contaminate large numbers of people by inhalation. If measures to reduce the internal dose are considered appropriate, oral administration of either calcium (Ca) or zinc (Zn) diethylenetriaminepenta-acetic acid (DTPA) would be the simplest treatment. Published experimental data from rats on the effects of oral DTPA on the retention of inhaled Pu and Am show that: (1) orally administered Zn-DTPA is as effective as repeated intravenous injection for the decorporation of Pu and Am inhaled as nitrates, although higher dosages are required; (2) oral Zn-DTPA appears to be an effective treatment for Am dioxide but not Pu dioxide; (3) maximum decorporation of Pu, by oral or intravenous administration, requires a large molar excess of Zn-DTPA over Pu (>1 x 10(6)); (4) neither oral nor injected Zn-DTPA are likely to be effective for Pu oxides, nor when Pu and Am nitrates are mixed with other dusts. It is concluded that oral administration of a simple aqueous solution of Zn-DTPA could be an important treatment in accident or emergency scenarios after intake of pure chemical forms of Pu and Am, which are highly or moderately soluble in biological fluids. However, more research is needed on the efficacy of treatment when these forms are mixed with other materials. Importantly, studies designed to increase the efficiency of uptake of DTPA from the gastrointestinal tract could appreciably reduce the dosage.