The average concentrations of naturally occurring radionuclides in drinking water are estimated from recent measurements and are used to estimate the annual effective dose equivalent associated with drinking water due to the different radionuclides. The annual effective dose equivalents are determined from the annual intake of these radionuclides using dosimetric information based on ICRP Publication 30 dosimetric models and cohort analysis considering risk coefficients developed by the U.S. Environmental Protection Agency using data from the report of the Biological Effects of Ionizing Radiation Committee (BEIR III) of the National Academy of Sciences. The resulting contribution from drinking water sources to the annual effective dose equivalent is in the range of 0.002 to 0.05 mSv/y (0.2-5 mrem/yr) for those using community drinking water supplies (approximately 216 million people in the United States). The contribution to the annual effective dose equivalent from 222Rn dissolved in water is in the range of 0.8-30 mu Sv/y (0.08-3 mrem/yr) based on the inhalation pathway following the release of 222Rn from drinking water.
Most of the results of the first systematic nationwide monitoring of public water supplies for 226Ra have been received. Approximately 50,000 public water supplies have been sampled of a total of 59,812. It is estimated that once the drinking water from all supplies has been analyzed, approx. 500 samples will exceed the Maximum Contaminant Level (MCL) of 5 pCi/l. Almost all the violations occur for ground water supplies. Monitoring in some states is incomplete but the geographical distribution of these water supplies that exceed the MCL is clear. This study is compared to other information concerning the concentration of 226Ra in drinking water supplies and the implications of this information are discussed.
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