Examination of the collected data for radionuclide concentration measurements in public water supplies in the United States show more than 51,000 measurements for gross alpha-particle activity and/or Ra, 89,900 measurements for U, and 9,000 measurements for Rn. These measurements were made as part of national and state surveys of radionuclide concentrations in utility water supplies for Ra and Rn; and the National Uranium Resource Evolution (NURE) survey for U which included non-utility water supplies. Surface water has low values for Ra and Rn but levels comparable to ground water for U. Separate isotope measurements were not taken for much of the Ra and U data. Because 226Ra to 228Ra ratios and 238U to 234U ratios are not fixed in water, further measurements are needed to establish the specific isotopic concentrations by region. Analysis of the state average values in geological provinces shows the highest provincial areas for Ra are the Upper Coastal Plain, the glaciated Central Platform, and the Colorado plateau. For U, the highest areas are the Colorado plateau, the West Central Platform, and the Rocky Mountains. For Rn, the highest provinces are New England and the Appalachian Highlands-Piedmont. Regional hydrogeological and geochemical models are suggested for guiding the formulation of regional standards and monitoring strategies. Utility supplies serving small populations have the highest concentration for each radionuclide and have the lowest fraction of samples measured, which shows a need for further measurements of these small population water supplies. Risk estimates for the average concentration of Ra in utility ground water give about 941 fatal cancers per 70.7-yr lifetime in the United States. Risk estimates for the average concentration of U in utility surface and ground water give about 105 fatal cancers per 70.7-yr lifetime in the United States. Using 1 pCi/liter in air for 10,000 pCi/l in water, the Rn in utility water risk estimate is for 4,400-22,000 fatal cancers per 70.7-yr lifetime in the United States.

A multicompartmental model is developed to simulate the biokinetics in the human body following the ingestion of an inert gas. It was assumed that 100% of the radon ingested appears in the stomach, from which it is transported through the body to different organs via the blood stream. Each of these organs absorbs and releases radon differently, and, amongst all, the fat retains radon for the longest time. To test the model, the information on elimination rates of 222Rn in expired breath was obtained from other experiments done at the University of Maine. The data included male and female participants with a wide range of ages and physical activity levels. The radiation doses in the different organs and tissues were computed. As was expected, the stomach sustained the maximum dose. In this study, the highest stomach dose to any volunteer was evaluated as 115 mSv y(-1).

An inexpensive, easy-to-use detector for measuring airborne 222Rn based on 222Rn diffusion and absorption in activated charcoal is presented. The detector uses chemical extraction and liquid scintillation for measurement of the 222Rn concentration, is designed to be insensitive to temperature and humidity effects, and obtains sensitivity levels of 675 CPM (Bq L-1)-1 [25 CPM (pCi L-1)-1] at room temperature.

The uptake, accumulation and loss of radionuclides by the American oyster (C. uirginica) acquacultured in the effluent of a nuclear power reactor has been measured monthly for 3 yr at four field stations in the Montsweag Estuary of the Sheeuscot River and at a control station in the nearby Damariscotta River Estuary, southern central coastal Maine, U.S.A. A mathematical model for the time variation of the specific activity of the oysters has been developed to include the physical half-lives of the various radionuclides, the biological half-lives of the various radionuclides (biological depuration), the water temperature (oyster hibernation) and shell growth. The resulting first order linear differential equation incorporating these phenomena is driven by the liquid radionuclide effluent release schedule of the Maine Yankee Nuclear Reactor. Comparison of the monthly measurements of the specific activity for 58C0, 6oCo, "Mn, 134Cs and I3'Cs in oysters with model calculations show close agreement over all ranges of variation observed. A special feature of this mathematical model is its ability to describe the non-chemostatic field situation. INTRODUCllONtics of the loss of radionuclides in chemostatic THE ROUTINE discharge of radionuc-aquarium experiments (Cr75). lides in the liquid effluent of nuclear powerIn the presentation that folbws, we discuss reactors sited on estuarial and coastal waters a mathematical model for the uptake, acprovides an ideal field situation for the testing cumulation and loss of radionuclides by OYSof mathematical models for the uptake, ac-ters (c. uirghica) cultured in the efflent Of a cumulation and loss of radionuclides in the nuclear power reactor. This field situation, marine ecosystem. Concentration factor mod-characterized by abrupt discharges of various els (p067), power law models (~~7 1 ) and ex-radionuclides in an aperiodic manner and with ponential models (Cu74; Hi69) have been varying concentrations, Seems to be adeused by various authors to describe the kine-quately described by the model Over the 36-tics of several radionuclides in marine organ-month experimentation Period. isms. Certain experimental situations and limiting cases are best described by one of these specific models. For example, the conIn order to measure the specific activity of centration factor model best describes a gamma-ray radionuclides, a group of about 20 steady-state condition or equilibrium concent-oysters were collected from each of five raftration; the details of the loss of bone-seeking ing stations, scrubbed with a stiff brush to radionuclides seem best described by a power remove fouling organisms and transported to law m d e l while single compartment the environmental radioactivity laboratory at models are usually used to describe the kine-the Universtiy of Maine, Department of 121 EXPERIMENTAL METHOD

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