![]() ![]() Drinking water obtained from surface supplies generally does not contain significant amounts of radium, and treatment processes, such as flocculation and water-softening, can remove the bulk of radium from water. Some groundwater may contain up to 100 pCi/liter. The radium-226 content of fresh surface water is variable, ranging from 0.01 to about 0.1 pCi/liter. Of these, radium-226 and its daughters and the daughters of radium-228 probably have the greatest potential for producing radiation doses of some consequence to man. The natural alpha-emitters that occur in drinking water appear to be bone seekers. The thorium content of drinking water has not been extensively measured, but its concentration in the human skeleton is about 1 fCi/g of ash the corresponding abundance of uranium in the skeleton is about 10 times greater. Concentrations of uranium in drinking water are extremely variable, apparently ranging from 0.02 to 200 µg/liter in fresh waters. The majority of them are alpha-emitters and include isotopes of polonium, radon, and radium (UNSCEAR, 1972, p. Radionuclides that are produced by the decay of uranium-238 and thorium-232 are widely distributed throughout the earth's crust. Consumption of 2 liters per day of such water might contribute as much as 8 pCi per day, but this is a negligible fraction of the total daily intake of 2,300 pCi of a nuclide that is the largest natural contributor to total body somatic and genetic dose. In 1970, some California drinking water, for example, contained up to 4 pCi/liter of potassium-40. Assuming that there is 0.2% potassium in soft tissue, a dose rate of 19 mrad per year has been estimated of this, 17 mrad are due to beta radiation (UNSCEAR, 1972, p. Since potassium concentrations in man seem to be under homeostatic control, wide fluctuations in drinking-water potassium would have negligible effects on internal concentrations. Adults in the United States ingest about 2,300 pCi of potassium-40 per day, but almost all of it is derived from foodstuffs. This primordial radionuclide occurs as a constant percentage (0.0118%) of total potassium. Of all the natural radionuclides that occur in water and emit low-LET radiation, potassium-40 is likely to be the most significant. In ocean water, the concentration might be about 0.1 pCi/liter (NCRP, 1975, p. In water containing about I mg of carbon per liter, a concentration of 0.006 pCi/liter might be expected. 29), is oxidized to 14CO 2, which is generally found at a concentration corresponding to about 6 pCi 14C per gram of carbon. In similar fashion, carbon-14, produced by cosmic ray interactions with atmospheric nitrogen (UNSCEAR, 1972, p. Tritium concentrations in water supplies vary from about 10 to 25 pCi/liter (Jacobs, 1968). ![]() It is then oxidized to tritiated water, which mixes into the hydrosphere. Tritium is produced by cosmic ray interactions with atmospheric oxygen and nitrogen. Some of the radionuclides that are responsible for the natural radioactivity in drinking water come from radioactive elements, and their decay products, that were incorporated in the earth at its formation, and others are produced continuously by cosmic ray bombardment. In some cases it was possible to take new published and unpublished information into account in this assessment of the probable effects of the radioactivity in drinking water on the population of the United States.Īmong the groups whose reports were used were: the National Academy of Sciences Advisory Committee on the Biological Effects of Ionizing Radiation (BEIR), the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the International Commission on Radiological Protection (ICRP), and the National Council on Radiation Protection and Measurements (NCRP). ![]() The Subcommittee on Radioactivity in Drinking Water has relied heavily on the reports of those other groups and has abstracted and summarized pertinent sections. Consequently, there is a large body of information on the biological effects of ionizing radiation. Some of these groups have also been responsible for establishing permissible levels of exposure. ![]() Since it was discovered that ionizing radiation produces detrimental biological effects, many national and international groups have studied the sources and levels of radiation to which the human population is exposed, and have estimated the corresponding biological effects. ![]()
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