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VRadioactivity In Drinking Water 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 ejects. Some of these groups have also been responsible for establishing permissible levels of exposure. Consequently, there is a large body of information on the biological effects of ionizing radiation. The Subcommittee on Radioactivity in Drinking Water has relied heavily on the reports of those other groups and has abstracted and summarized pertinent sections. In some cases it was possible to take new published and unpublished information into account in this assessment of the probable ejects of the radioactivity in drinking water on the population of the United States. Among the groups whose reports were used were: the National Academy of Sciences Advisory Committee on the Biological Ejects of Ionizing Radiation (BEIR), the United Nations Scientific Committee on the Ejects of Atomic Radiation (UNSCEAR), the International Com- mission on Radiological Protection (ICRP), and the National Council on Radiation Protection and Measurements (NCRP). BACKGROUND RADIATION The natural ionizing radiation, to which all people are exposed, includes cosmic rays and products of the decay of radioactive elements in the 857

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858 DRINKING WATER AND H"LTH TABLE VII-1 Estimated Total Annual Whole-Body Doses from Natural Radiation in the United States (from BEIR Committee, 1972) Source Annual Doses, mrem Cosmic rays Terrestrial radiation External Internal Total 44 40 18 102 earth's crust and atmosphere. Part of the terrestrial radiation dose is from sources external to the body, and part is due to the inhalation and ingestion of radioactive elements in air, food, and water. In the United States, this unavoidable background radiation gives, on the average, an annual dose of about 100 mrem to the population (Table VII-1~. There is, however, great variability in the amount of background radiation, which depends on regional geological characteristics and altitude. It has been found, for example, that the annual background dose in Colorado is 100 mrem (or more) higher than that in Louisiana (BEIR Committee, 1972~. Mankind has always lived with such radiation, to which, however, the radionuclides in drinking water contribute but a small share. ABUNDANCE OF RADIONUCLIDES IN WATER Minute traces of radioactivity are normally found in all drinking water. The concentration and composition of these radioactive constituents vary from place to place, depending principally on the radiochemical composition of the soil and rock strata through which the raw water may have passed. Many natural and artificial radionuclides have been found in water, but most of the radioactivity is due to a relatively small number of nuclides and their decay products. Among these are the following emitters of radiation of low linear energy transfer (LET): potassium-40 (40K), tritium (3H), carbon-14 (TIC), and rubidium-87 (87Rb). In addition, high-LET, alpha-emitting radionuclides, such as radium-226 (226Ra), the daughters of radium-228 (228Ra), polonium-210 (tempo), uranium (U), thorium (Th), radon-220 (220Rn), and radon-222 (222Rn), may also be present in varying amounts.

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Radioactivity in Drinking Water 859 Natural Radionuclides SOURCES OF LOW-LET RADIATION Some of the radionuclides that are responsible for the natural radioactivi- ty 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. Tritium is produced by cosmic ray interactions with atmospheric oxygen and nitrogen. It is then oxidized to tritiated water, which mixes into the hydrosphere. Tritium concentrations in water supplies vary from about 10 to 25 psi/liter (Jacobs, 1968~. In similar fashion, carbon-14, produced by cosmic ray [~4N(n,p)~4C] interactions with atmospheric nitrogen (UNSCEAR, 1972, p. 29), is oxidized to SCOW, which is generally found at a concentration corre- sponding to about 6 psi )4C per gram of carbon. In water containing about 1 mg of carbon per liter, a concentration of 0.006 psi/liter might be expected. In ocean water, the concentration might be about 0.1 psi/liter (NCRP, 1975, p. 351. Of all the natural radionuclides that occur in water and emit low-LET radiation, potassium-40 is likely to be the most significant. This primordial radionuclide occurs as a constant percentage (0.0118~o) of total potassium. Adults in the United States ingest about 2,300 psi of potassium-40 per day, but almost all of it is derived from foodstuffs. Since potassium concentrations in man seem to be under homeostatic control, wide fluctuations in drinking-water potassium would have negligible ejects on internal concentrations. 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. 30~. In 1970, some California drinking water, for example, contained up to 4 psi/liter of potassium-40. Consumption of 2 liters per day of such water might contribute as much as 8 psi per day, but this is a negligible fraction of the total daily intake of 2,300 psi of a nuclide that is the largest natural contributor to total body somatic and genetic dose. SOURCES OF HIGH-LET RADIATION Radionuclides that are produced by the decay of uranium-238 and thorium-232 are widely distributed throughout the earth's crust. The majority of them are alpha-emitters and include isotopes of polonium, radon, and radium (UNSCEAR, 1972, p.31~. Concentrations of uranium in drinking water are extremely variable, apparently ranging from 0.02 to

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860 DRINKING WATER AND H"LTH 200 ~g/liter in fresh waters. 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. The natural alpha-emitters that occur in drinking water appear to be bone seekers. 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 radium-226 content of fresh surface water is variable, ranging from 0.01 to about 0.1 psi/liter. Some groundwater may contain up to 100 psi/liter. Drinking water obtained from surface supplies generally does not contain significant amounts of radium, and treatment processes, such as flocculation and water-soften- ing, can remove the bulk of radium from water. In the Midwest of the United States there is an area where groundwa- ters contain significant levels of radium-226 and radium-228. This area primarily in Iowa, Illinois, Wisconsin, and Missouri includes an estimated population (1960 census) of approximately 1 million persons. The weighted mean concentration of radium-226 has been estimated to be approximately 5 psi/liter (Peterson et al., 1966~. Rowland, Lucas, and Stehney (1975) have reported that approximately 500,000 people in Illinois and Iowa have drinking water supplies whose radium-226 content is 3 6 psi/liter; about 300,000 people, 6-9 psi/liter; and about 120,000 people live in areas where well water contains 9-80 psi/liter of radium- 226. A personal communication (Rowland, Lucas, and Stehney, 1976) from the same investigators stated that, of the last group, 113,000 people drink water that contains less than 20 psi/liter, and 5,700, 20-25 psi/liter. The one community (1,200 persons) that had a well in which 80 psi/liter of radium-226 was found, now uses water from a well containing only 3 psi/liter. In addition, a survey in 1966 that was designed to locate water supplies with high concentrations of radium found water supplies with more than 3 psi of radium-226 per liter in areas other than those of the northern Midwest described above (Hickey and Campbell, 1968~. These supplies served approximately 145,000 people. Thus, it appears that in the entire United States approximately 1.1 million people consume water that contains more than 3 psi/liter of radium-226. The major additional contribution to the alpha-emissions in drinking water is due to the decay of radium-228; although other alpha-emitting natural radionuclides have been found in drinking water, they occur in exceedingly small concentrations. For example, one analysis of water containing 5 psi of radium-228 per liter was found to contain less than

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Radioactivity in Drinking Water 861 0.02 psi/liter of thorium isotopes and only 0.03 psi/liter of uranium (Stehney, 1960~. Two other radium isotopes may be present in drinking water, but although both radium-223 and radium-224 may contribute to the gross alpha activity of water measured soon after drawing from the tap, their contributions to the long-term dose deposited in the skeleton are negligible because they have short half-lives. However, radium-228, which decays by beta emission, and therefore does not contribute to gross alpha activity in drinking water, will, as a result of its subsequent decay scheme, give rise to a series of alpha-emitting daughter products. It is these radium-228 daughter products, and radium-226 and its daughters, that produce, in our opinion, the major alpha-particle dose to the tissues of the body, particularly to the skeleton. Thus, when discussing radium in drinking water, it is essential to distinguish between the isotopic mixture measured in freshly drawn drinking water and the long-term alpha dose that might be accumulated in tissue. Because of the different decay schemes for radium-226 and radium- 228, different alpha doses are received under equilibrium conditions from each of these two radium isotopes. In waters of low alpha-particle radioactivity, the activity concentration of radium-228 is generally equal to that of radium-226, whereas at high radioactivity concentrations it is only half that of radium-226 (Lucas and Krause, 1960~. The abundance of the radioactive gas radon-222, which is formed by the decay of radium-226, is not highly correlated with the radium concentration in fresh water. Radon concentration is generally 1 psi/liter in surface water, but activity concentrations in groundwater are typically a few thousand times greater. Some mineral or spa waters, however, may contain 500,000 psi/liter. Consumption of water containing 1 ,uCi of radon-222 will result in a stomach dose of about 20 mrads, but the doses to other organs will be lower by at least a factor of 10 (UNSCEAR 1975, p. 35~. Furthermore, consumption of 2 liters per day of water containing 1 nCi/liter of radon- 222 would deliver an annual stomach dose of about 12 mrad. In three large American cities, the total daily intake of uranium, radium-226, radium-228, and lead-210 in water have all been quoted to range approximately between 0.01 and 0.05 psi/day (NCRP, 1975, p. 92~. When compared with other components of the diet, drinking water usually contributes less than about 2% of these alpha-emitting radionu- clides to the daily dietary intake (NAS-NRC, 1973~. The greatest dose potential from alpha-radiation from naturally occurring radionuclides in drinking water will be related to the ingestion of radium-226 in areas where its concentration is high.

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862 DRINKING WATER AND H"LTH Artificial Radionuclides To some extent, all drinking water obtained from surface sources will reflect contamination from atmospheric testing of nuclear weapons. Extensive measurements have been made of the contribution of airborne fission products to drinking water contamination and in particular to the levels that were produced by testing weapons before the Nuclear Test Ban Treaty of 1963. The sharp decrease in radioactive fallout since that date has been followed by a corresponding decrease in the radioactivity of surface water. Although the analyses are not very extensive, the temporal characteristics provide some information that is useful in predicting the transport and fate of radionuclides in water. Some of the longer-lived radionuclides still persist from early tests, together with smaller quantities of fission products injected irregularly into the atmosphere from the testing of weapons by nontreaty nations. Many of the states conduct periodic surveys of the radioactivity of drinking water. Unfortunately, these consist, for the most part, in counting only the gross beta and gross alpha activity in the water. In addition, there is a considerable body of data on the temporal patterns and regional concentrations of the fission products strontium-90 and cesium- 137, the physical half-lives of which are about 30 yr. There appears to be a fairly good correlation between the measurement of solids in finished water and radioactivity content measured as beta activity (Figure VII-1~. It is likely that potassium-40 in soil suspensions might account for such an observation. Because they account for a major part of the potential dose from nuclear fission and activation products, and because of their biological significance, considerable attention has been devoted to strontium-90, cesium-137, iodine-131, tritium, and carbon- 14 as potential water contaminants. These, however, are not necessarily correlated with the solids content of drinking water. Sources of man-made radionuclides, in addition to atmospheric weapons tests, include local discharge of radiopharmaceuticals and the possible entry of radioactivity into watersheds from the use and processing of nuclear fuel to produce electric power. RADIOPHARMACEUTICALS The release of radioactive materials in the exhaust air and liquid wastes from medical institutions has been studied many times in different locales. No evidence yet suggests a drinking-water hazard from medical effluents. This conclusion is based on data collected in many surveys

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Radioactivity in Drinking Water 863 1000 Q 800 In o In > 600 o n In ~ 400 o 200 o o O / / O / O o - 0/ // 8o8 O / 1 1 1 1 1 0 10 20 RADIOACTIVITY (psi/Liter) 30 40 50 FIGURE Vll-l Relationship between total dissolved solids and radioactivity of California domestic water. Goldberg ( 1976). (Soda et al., 1975; Gesell et al., 1975; Klement et al., 1972; Kaul and Loose, 1975~. The agents to which particular attention was given in these surveys were radioactive iodine and technetium-99m. Both are widely used in medical practice, and there is special concern over the iodine isotopes, because of their potential effects on the thyroid gland. Since 1950, eight groups have reported on the extent of release of radioisotopes in areas of the United States where there were active clinical nuclear medicine programs. Because of recent rapid increases in

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864 DRINKING WATER AND H"LTH the numbers and kinds of procedures being conducted, Sodd et al. (1975) studied the use and discharge of iodine-125, iodine-131, and technetium- 99m in the Cincinnati area. They measured the radioactivity from these nuclides in the influent, effluent, and sludge at the sewage-treatment plant, as well as the activity in the Ohio River 10 miles above and 5 miles below the plant. Gesell et al. (1975) conducted a similar survey of medical usage and concentrations in sewage of iodine-131 and technetium-99m in the Houston area. The general conclusions reached by both groups indicated that the eject on levels of radioactivity in drinking water of the medical usage of radioisotopes that they studied appears to be of negligible importance. The Cincinnati study was centered about the largest sewage treatment plant serving that city. This plant receives the effluent from 10 hospitals that use radionuclides in clinical nuclear medicine. Approximately 60% of the patients were outpatients, so control of biological wastes was not attempted. Radioactivity in the sludge accumulated at the plant exceeded that in the water. Sludge concentrations of iodine-131 and technetium- 99m were measurable, but that of iodine-125 was below the limit of detectability (10 psi/liter). It was estimated that between logo and 30~o of the total amount of technetium-99m given to patients in Cincinnati hospitals was discharged in sewage effluent into the Ohio River. Typically, about 300 mCi/week of this nuclide were estimated to reach the river, where dilution with river water was calculated to give concentrations downstream of about 1 psi/liter. In fact, analysis of river water showed identical values upstream and downstream of 3-4 + 3 psi/liter. These are lower, by a factor of about a million, than the current maximum permissible concentration (6 ,uCi/liter; NRC, 1976) of technetium-99m in water for the general population. Comparable results were obtained for iodine-131. Smaller amounts were used, and the concentrations in sludge and water were lower than those of technetium. No differences between upstream and downstream levels were detected. Under the assumption that the same dilution had occurred, the medical uses of iodine-131 in the area were calculated to produce a maximal increase in concentration in the river of about 0.3 psi/liter. This value is about one thousandth of the current maximum permissible concentration of iodine-131 in water (300 psi/liter; NRC, 1976) for the general population. Thus, at present, given current rates of use, patterns of disposal, and radiation protection guidelines, many orders of magnitude separate the concentrations of radioactivity in drinking water due to medical uses of radioisotopes from conceivably hazardous levels. Projections of the rate

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Radioactivity i' n Drinking Water 865 of increase in use of radiopharmaceuticals have been made by the Environmental Protection Agency (Klement et al., 1972~. They estimate that there may be a 12-fold increase in the medical use of these agents by the year 2000, on the basis of the annual increments in whole-body radiation dose from the use of these agents in medicine. This represents a very small incursion, and probably will not be measurable. NUCLEAR FUEL CYCLE ACTIVITIES Among the major effluents from the use and processing of nuclear fuel are tritium, plutonium, and krypton. Of these, only tritium, which is released as a gas, and plutonium can possibly enter water supplies. The predominant form of plutonium release from nuclear power and processing plants is as an aerosol that will have little or no impact on drinking water. Although a single incident has occurred in which as much as 18,750 Ci of plutonium were released from liquid storage on a local basis, none apparently reached opposite water supplies (AEC, 1974, pp. 49- 50~. The usual rate of release from liquid storage at controlled sites is about 1 mCi/yr. Continuing improvement in methods of storage should further reduce this rate. Nevertheless, the adequacy of monitoring water supplies in the vicinity of nuclear facilities should be reviewed periodical- ly. Because of its exceedingly long half-life (1.7 x 107 yr), the possible consequences of the release of iodine-129 during nuclear fuel reprocess- ing were considered. This radionuclide has a specific activity of about 173 ,uCi/g. In a recent review, Soldat (1976) calculated that the maximal isotope ratios of i29I:~27I would be about 10~ in water near nuclear facilities. His calculations indicate that consumption of 2 liters/day of water containing iodine-129 at 1 psi/liter deliver an annual thyroid dose of about 5 mrem to an adult and about 10 mrem to an infant. Peak activities in water have been reported to be about 0.01 psi/liter, which would correspond to an annual thyroid dose of about 0.05 mrem to an adult. RADIATION DOSE CALCULATIONS Estimates of the radiation doses expected to be produced by radionu- clides ingested in water were calculated by means of the methods and parameters given in NCRP Report 22 (NBS Handbook 69, 1963 revision) and ICRP Publication 2 (ICRP, 1959~. To approximate the equilibrium

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866 DRINKING WATER AND HEALTH levels that take into account build-up, retention, decay, and elimination of various radionuclides, annual doses were computed for the fiftieth year of constant intake of 1 psi/year, and 2 liters per day of water containing 1 psi/liter. These doses are presented in Table VII-2. At earlier times, the annual doses may be lower than those shown, and for a few long-lived radionuclides (e.g. 90Sr, 226Ra), they may never reach equilibrium, but the values in Table VII-2 are within 204Yo of the theoretical equilibrium levels. These values were obtained by using the NCRP and ICRP metabolic and dosimetric models for all radionuclides, except for the isotopes of the alkaline earth elements radium and strontium, which are discussed below. ISOTOPES OF ALKALINE EARTH ELEMENTS For the alkaline earth elements, the recent metabolic model of ICRP Publication 20 (1973) was used. In its 1959 report on permissible doses (ICRP, 1959*), Committee II of the ICRP used an exponential model of retention for all radionuclides to calculate maximum permissible concentrations in water. The committee pointed out, however, that there was good evidence that retention of radium-226 and other bone-seeking radionuclides is best represented by a power function model (Norris et al., 1958~. In the case of radium-226, the calculated body burden from intake at constant daily rate for 50 yr is about a factor of 10 smaller by the power function model than by the ICRP exponential model. This may be shown by use of the equations and the values for metabolic parameters that are given in the ICRP report. Ingestion of 1 psi of radium-226 per day in water is assumed in the sample calculations given below. According to the ICRP exponential model, the amount of a radionu- clide, ~f2, that accumulates in an organ from constant ingestion rate, a, is given by: qf2 afw o 693 (1-e--0 693 Tic) where q= total amount in the body,f2 = fraction of q in the organ of reference (0.99 for bone), fw = fraction of radionuclide ingested in water *The maximum permissible concentrations of radionuclides in ICRP 1959 and NCRP 1963 are identical.

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Radioactivity in Drinking Water 867 _ >, C C eD tO P) ~} ~4 ~ tn _ ~ _ _ ~ ~ c | . ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ O O O O O 0 00 0 0 0 0 0 0 0 0 0 00 0 0 0 3 . ~ x x x x x x x x x x x x x x x x x x x x x ~ ~0 ~ ~ O ~ - -r~ oo V) ~ v~ ~ ~ ~ ~ ~ ~ =. ~D ~ O .= - E ~x ~ r~ ~ r~ ~ ~ ~ \0 ~ ~ oo ~ - - ) \0 ~ ~ -} - ) - c~ .3 . D _ CL .= ~ 3 _ ~ ~ m ~ '.} E ~Z N N N ~ 1 1 o 1 1 o o O O O O O O O ~ ~ . ~ ~ O O ~ . . . _! r~ r~ ',, X X X ~ ~ ~ O ~ -`C _ _ _ 1 o o _ _ o 1 1 O O O O O O O O ________ X X X X X X X X X O oo ~ ~ r~ ~ oo . . .. . . _ _Cr,~ iV~) 3 ~ '- ~ ~ .- ~ m m c: ~ ~ ~ ~ ~ m m m m m ~ ~ c~ ~ r ~ ~ tq ~ ~ ~ ~r ~ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 _ ______ ________ x x x x x x x x x x x x x x x ~. _ - , 0 - ~ ~ 1 1 1 - 1 ~ ~ ~ ~ ~ - 1 1 - - ~ ~ ~- ~ ~ .c: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 _ __________ ________ __ x x x x x x x x x x x x x x x x x x x x x - 1- d 1- r-} \= ~ ~O ON ~ ~1- ~ - sC~ ~t ~C~ 1- - (S~ v-, ON . . . . . . . . . . . . . . . . . . . . . _ v~. ~ x ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ a a a a a a a a a a ~ ~ O ~ ~ _. ~ ^ _. N ~ ~ ~ ~ - - ~ N ~ ~ - - ~'-. X ~_. _. _. - - - - - N N N N N N N - 11 a . CL - o - 3 X ~ ~Ct C ;~. D D ,y U) C ._ - Ct .C ~C Cd C ~ . _ ~ o Ct ', C ~ .. O V. ~ _ _ C _ C`, U7 ~ U, U) O O O V' .0 _ ~3 ~ O ~ D - r~ eq ~ O b. - o ~4 C iq ~ U~ o ~ C C ~ ~ _ O P ~ C ~ 3 .~C Z UO, ~ ~ C O o~ U~ O C. ~ ~ m >~ ~ .0

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894 DRINKING WATER AND H"LTH induced by the radiation: developmental and teratogenic risks, genetic risks, and somatic risks. Developmental and Teratogenic Risks Although the developing fetus is sensitive to radiation, the total low-dose- rate doses that would be delivered during the sensitive periods of gestation are so small that no measurable ejects of the radiation from drinking water will be found. The lowest dose level at which any eject has been reported is 3 mrem/day or 1,100 mrem/yr in contrast to the 0.244 mrem per year described above. Genetic Risks For the general population, the maximum permissible dose of man-made radiation is 170 mrem/yr, excluding medical uses of radiation. This amounts to a 5 rem genetic dose in each 30-yr generation. This dose would increase the current incidence of genetic diseases, which is about 94,400 per million live births, by about 200 per million in the first generation. The estimate of 200, however, is so uncertain that there are very large limits about the value. The gonadal dose of 0.244 mrem/yr calculated for the hypothetical drinking water is expected to increase the genetic diseases from the 94,000/106 live births by 200x0.244 mrem/30x 170 mrem = 0.0098 additional genetic diseases per million live births per year. Since there are approximately 3.6 million live births in the United States each year, this is an increase of 0.035 total genetic diseases in the United States per year. If one takes the unlikely extreme limits of the estimated genetic hazards of radiation (about 4,000) instead of the value 200, the increase is 0.7 cases per year. Somatic Risks The natural background of radiation can be estimated to cause 4.5 to 45 fatal cases of cancer per year per million people, depending on the risk model used to make the calculation (Table VII-l 1~. Less than 1% of this will be contributed by the radionuclides in drinking water. Variations in the radium content of drinking water, however, may cause appreciable differences in the radiation dose to the skeleton and, in turn, in the risks of associated carcinogenic ejects. Under average conditions, the annual dose to bone from radium amounts to approxi- mately 6.4 mrem/yr, which represents about 6% of the total dose to the skeleton from all sources of natural background radiation (roughly 100

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Radioactivity in Drinking Water 895 mrem annually). The highest radium levels in drinking water (25 psi/liter of 226Ra and an additional 12.5 psi/liter of 228Ra), however, may be expected to deliver a dose to the skeleton of about 600 mrem/yr, which would represent a sixfold increase in the total dose to bone from all natural sources combined. If the carcinogenic risks associated with skeletal irradiation are assumed to be 0.2 fatal cases of bone cancer per million persons per year per rem (Table VII-9), then for a period up to 30 yr, in a population with a typical distribution of ages, the risks attributable to natural background radiation can be estimated to range up to about 0.6 per million persons per year under average conditions,* and to 4.2 per million per year under conditions of maximal intake of radium in the drinking water (about 600 mrem/yr from the radium). In addition to these risks, the possibility of carcinogenic ejects from radium on cells adjacent to bone, such as those in epithelia lining cranial sinuses and those in the bone marrow, should also be mentioned. However, the risks of such effects are likely to be appreciably smaller and cannot be estimated precisely from existing data. In comparison with the overall risks of cancers of all sites combined, of which 4.5 to 45 (i.e. 9000/200) fatal cases per million per year can be attributed to natural background radiation at average levels (Table VII-11), the additional 3.6 fatal bone malignancies per million per year ascribable to maximal intakes of radium in drinking water constitute a significant increment. It should be noted that only about 120,000 people drink water estimated to contain between 9 and 25 psi/liter. Thus the excess bone cancers in this group would be between 0.16 and 0.43 per year; that is to say, one excess bone cancer every 2 to 6 yr. Since about 113,000 of the 120,000 people drink water containing less than 20 psi/liter, the true number of excess bone cancers will lie somewhere towards the lower end of the range. When interpreting the above estimates, it must be remembered that they depend on dose-response models that remain highly uncertain. For example, the value given for the combined frequency of deaths from all types of cancer attributable to natural background radiation namely, 45 deaths per million per year is higher by a factor of three or more than estimates derived with any of the other risk models cited (Table VII- l l). Likewise, the corresponding risk estimates for skeletal cancer could vary widely, depending on the postulated dose-response relationship. Although the value yielded by the BEIR Committee's absolute risk model (0.2 fatal cancers per million per year per rem) is not greatly different from the value yielded by the BEIR Committee's relative risk model (since 9 out of the 1,704 fatal cancers per million per year are bone *(0.2 fatal cases x 0.1 rem/yr x 30 yr)/(106 persons per yr per rem)

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896 DRINKING WATER AND H"LTH cancers, this would be approximately 0.09 fatal bone cancers per million per year per rem), both models, in postulating a linear nonthreshold dose-response relationship, give substantially higher estimates than do models postulating dose-dependent and dose-rate-dependent variations in the risk per rem. Given the uncertainties in present knowledge, the BEIR Committee's absolute risk model as used in the foregoing would seem to provide an acceptably conservative approach for the purposes at hand. SUMMARY RADIOACTIVITY IN DRINKING WATER Everyone is exposed to some natural radiation that comes from both cosmic rays and terrestrial sources. Although there are large geographic variations in the amount of natural background radiation, the average background dose in the United States is about 100 mrem/yr. A small proportion of this unavoidable background radiation comes from drinking water that contains radionuclides. By far the largest contribution to the radioactivity in drinking water comes from potassium-40, which is present as a constant percentage of total potassium. Only a small percentage of the total potassium40 body burden, however, comes from drinking water. The total body dose from other possible radioactive contaminants of water constitutes a small percentage of the background radiation to which the population is exposed. Although the amounts of individual radioactive contaminants fluctuate from place to place, calculations made for a hypothetical water supply that might be typical for the United States have shown that a total soft-tissue dose of only 0.24 mrem/yr would be contributed by all the radionuclides found in the water. Even with rather wide fluctuations in the concentrations, the total contribution of the radionuclides will remain veer small. However, bone-seeking radionuclides such as strontium-90, radium- 226, and radium-228 account for a somewhat larger proportion of the total bone dose. This is particularly true for the two isotopes of radium because they, or their daughters, emit high-linear-energy-transfer (LET) radiation, and because certain restricted localities have been found to have rather high concentrations of radium in drinking water. Neverthe- less, in the hypothetical typical water supply, less than lOgo of the annual background dose comes from such radiation. It has also been estimated that the total population exposed to levels of radium greater than 3 psi/liter is about a million people. About 120,000 people are exposed to radium at levels greater than 9 psi/liter.

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Radioactivity in Drinking Water 897 Risk estimates were made of three kinds of adverse health ejects that radiation could produce: developmental and teratogenic effects, genetic effects, and somatic (chiefly carcinogenic) effects. Developmental and Teratogenic Effects The developing fetus is exposed to radiation from radionuclides in drinking water for nine months. Thus, the total dose accumulated by the fetus will be very small. Furthermore, although the fetus is sensitive to the effects of radiation in some stages of development, these periods are sharply limited and extremely short. For this reason, too, the total dose administered that could possibly have developmental and teratogenic effects would be extremely small. Current concentrations of radionu- clides in drinking water lead to doses of about one five-thousandth of the lowest dose at which a developmental effect has been found in animals. Therefore, the developmental and teratogenic effects of radionuclides would not be measurable. Genetic Effects It has been estimated that there are about 94,400 genetic diseases per million live births in the United States. The maximum permissible dose of man-made radiation for the general population (170 mrem/yr) has been estimated to increase this number in the first generation by 17~215, with an unlikely upper limit of 4,250. On the basis of a 30-yr generation and 3.6 million live births per year in the United States, we would expect the 0.24 mrem soft-tissue dose, or gonad dose, to lead to 0.0098 additional cases of genetic disease per million live births per year or 0.035 additional cases of genetic disease in the United States per year. Even at the unlikely extreme upper limit of possible genetic effects of radiation of around 4,000 extra cases in the first generation, there would still be less than one additional case per year in the 94,400x3.6 = 340,000 live births with genetic defects. The wide fluctuation in bone dose caused by fluctuations in the radium concentration of drinking water would not have any sensible effect on the genetically significant dose, because radium is predominantly a bone seeker and will deliver very little radiation to the gonads. Somatic and Carcinogenic Effects The natural background of radiation can be estimated to cause 4.5 to 45 cases of cancer per million people, depending on the risk model used. The

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898 DRINKING WATER AND H"LTH per year amount of whole-body radiation from radionuclides in typical drinking water contributes less than 1% of this amount, and thus, for cancers other than those in bone, may cause a negligible increase in the total. Radium, however, can contribute somewhat less than 7% of the total bone dose received from background radiation in areas of "normal" radium concentration. The average carcinogenic risk associated with skeletal irradiation by radium in a population with a typical distribution of ages is estimated to approximate 0.2 fatal cases of bone cancer per million persons per year per rem. Therefore, over a period from 10 to 40 yr after the beginning of skeletal irradiation, the average risk attributable to natural background radiation is estimated to range from 0.6 per million persons per year, under typical conditions, to as much as 4.2 per million per year, in regions where 25 psi/liter of radium-226 are found in the drinking water. It has been noted that in the United States 120,000 people are estimated to drink water containing between 9 and 25 psi/liter of radium-226, and only a small number lie near the upper end of this range. The number of excess cancers in this group would therefore lie between 0.16 and 0.43 per year. Since not all the 120,000 people drink water containing 25 psi/liter of radium-226, the latter number is inordinately high. CONCLUSIONS The radiation associated with most water supplies proportion of the normal background to which all human beings are exposed, that it is difficult, if not impossible, to measure any adverse health ejects with certainty. In a few water supplies, however, radium can reach concentrations that pose a higher risk of bone cancer for the people exposed. FUTURE NEEDS is such a small The precision of estimation of the health risks associated with radioactivi- ty in drinking water could be enhanced if several water systems were analyzed to determine the complete distributions of beta and alpha radiation that constitute the gross counting measurements. Because the precise ratio of radium-228 to radium-226 in water has not been measured extensively, an attempt should be made to determine the ratio in several ground and surface waters whose content of radium-226 is known. Activity concentrations of the waters to be analyzed should range

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Radioactivity in Drinking Water 899 from about 0.1-50 psi/liter. The percentage of the daughter radionu- clides present should be determined. Because radon is a noble gas that is quickly released from water, it is possible that, in some areas of high radon content, water vapor containing radon might constitute an inhalation hazard when such water is used, for example, in humidifiers or for showers. A determination should be made whether or not radon emanations from water do indeed constitute an inhalation hazard. The models used in this report do not take into account the possibility that the finely divided solid particles that occur in water may alter the uptake of radionuclides. The elects of the solids in drinking water on the metabolism and uptake of radionuclides merit investigation. GLOSSARY Absolute risk. Excess or incremental risk due to exposure to a toxic or injurious agent (e.g., to radiation). Difference between the risk (or incidence) of disease or death in the exposed population, and the risk in the unexposed population. Usually expressed as number of excess cases in a population of a given size, per unit time, per unit dose (e.g., cases/106 exposed population/year/rem). Curie (Ci). Unit of radioactivity. 1 Curie = 3.7 x 10~ nuclear transformations per second. Some fractions are: millicurie (1 mCi = 1O-3 Ci), microcurie (1 ,uCi = 10-6 Ci), nanocurie (1 nCi = 10~ Ci), picocurie (1 psi = 10-~2 Ci), femtocurie (1 fCi = 1O-~5 Ci). Latent period. Period between time of exposure to a toxic or injurious agent and appearance of a biological response. LET. Linear energy transfer. Average amount of energy lost by an ionizing particle or photon per unit length of track in matter. Plateau period. Period of above-normal, relatively uniform, incidence of disease or death in response to a toxic or injurious agent. Rad. Unit of dose or radiation (energy) absorbed in any medium, except air. 1 Rad = 100 erg/g. Relative risk. Ratio of the risk in the exposed population to that in the unexposed population. Usually given as a multiple of the natural risk. Rem. Unit of radiation dose equivalence. Numerically equal to absorbed dose in red multiplied by a quality factor that expresses the biological effectiveness of the radiation of interest, and other factors. Equal doses expressed in rem produce the same biological effects, independently of the type of radiation involved.

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900 DRINKING WATER AND H"LTH Roentgen (R). Unit of radiation (energy) absorbed in air. 1 R = 2.58 x 1O-4 coulomb/kg of air. REFERENCES Abrahamson, S., and S. Wolff. 1976. Reanalysis of radiation-induced specific locus mutations in the mouse. Nature 264:715-719. AEC. 1974. Plutonium and other transuranium elements: Sources, environmental distribu- tion and biomedical effects. WASH-1359, U.S. Atomic Energy Commission. BEIR Committee. 1972. The ejects on populations of exposure to low levels of ionizing radiation. Advisory Committee on the Biological Effects of Ionizing Radiations, National Academy of Sciences, National Research Council, Washington, D.C. Batchelor, A.L., R.J.S. Phillips, and A.G. Searle. 1969. The ineffectiveness of chronic irradiation with neutrons and gamma rays in inducing mutations in female mice. Br. J. Radial. 42:448-45 1. Brent, R.L., and R.O. Gorson. 1972. Radiation exposure in pregnancy. Curr. Probl. Radial., vol. 2, no. 5. Brewen, J.G., R.J. Preston, and N. Gengozian. 1975. Analysis of X-ray-induced chromo- somal translocations in human and marmoset stem cells. Nature 253:468470. Cahill, D.F., L.W. Reiter, J.A. Santolucito, G.T. Rehnberg, M.E. Ash, M.J. Fauor, S.J. Bursian, J.F. Wright, and J.W. Laskey. 1976. Biological assessment of continuous exposure to tritium and lead in the rat. In Symposium on Biological Effects of Low-Level Radiation Pertinent to Protection of Man and His Environment, Chicago, 1975. International Atomic Energy Agency, Vienna. Cavalli-Sforza, L.L., and W.F. Bodmer. 1971. The Genetics of Human Populations. W.H. Freeman and Company, San Francisco. Della Rosa, R.J., M. Goldman, H.G. Wolf, and L.S. Rosenblatt. 1972. Application of canine metabolic data to man. In Biomedical Implications of Radiostrontium Exposure. AEC Symposium Series No. 25. CONF-710201:52-67. U.S. Atomic Energy Commission. EPA. 1975. Preliminary Assessment of Suspected Carcinogens in Dunking Water. Report to Congress, U.S. Environmental Protection Agency, Washington, D.C. Gesell, T.F., H.M. Pritchard, E.M. Othel, L. Prittle, and W. Di Pietro. 1975. Nuclear Medicine Environmental Discharge Measuremets. Final report to EPA, University of Texas, Houston, Office of Radiation Programs, U.S. Environmental Protection Agency. Goldberg, J. 1976. California Department of Health, Radiologic Health Section. Personal communication. Hickey, J.L.S., and S.D. Campbell. 1968. High radium-226 concentrations in public water supplies. Public Health Rep. 83:551-557. ICRP. 1959. Permissible Dose for Internal Radiation. International Commission on Radiological Protection. Publication No. 2. Pergamon Press, New York. ICRP. 1963. Report of the RBE Committee to the International Commissions on Radiological Protection and on Radiological Units and Measurements. International Commission on Radiological Protection. Health Phy. 9:357-386. ICRP. 1969. Radiosensitivity and Spatial Distribution of Dose. International Commission on Radiological Protection. ICRP Publication No. 14. Pergamon Press, New York. ICRP. 1973. Alkaline Earth Metabolism in Adult Man. International Commission on Radiological Protection. Publication No. 20. Pergamon Press, New York.

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902 DRINKING WATER AND H"LTH NCRP. 1975. Natural Background Radiation in the United States. NCRP Report No. 45. National Council on Radiation Protection and Measurements, Washington, D.C. NCRP. 1976. Influence of dose rate and LET on dose-effect relationships: Implications for estimation of risks of low-level irradiation. Report prepared by NCRP Scientific Committee 40. National Council on Radiation Protection and Measurements, Washing- ton, D.C. To be published. Newcombe, H.B. 1975. Mutation and the amount of human ill health. In O.F. Nygaard, ELI. Adler, and W.K. Sinclair, eds. Radiation Research, Proceedings of the Fifth Internation- al Congress of Radiation Research. Academic Press, New York. Norris, W.P., T.W. Speckman, and P.F. Gustafson. 1955. Studies of the metabolism of radium in man. Am. J. Roentgenol. 73:785-802. Norris, W.P., S.A. Tyler, and A.M. Brues. 1958. Retention of radioactive bone-seekers. Science 128:456-462. NRC. 1975. Reactor safety study; an assessment of accident risks in U.S. commercial nuclear power plants. WASH-1400, NUREG-75/014. U.S. Nuclear Regulatory Commis- sion, Washington, D.C. NRC. 1976. Standards for Protection Against Radiation. Nuclear Regulatory Commission, Title 10 Code of Federal Regulations, Part 20. U.S. Government Printing Office, Washington, D.C. Peterson N. .J., L. D. Samuels, H. F. . Lucas, and S. P. Abrahams. 1966. An epidemiologic approach to low-level radium-226 exposure. Public Health Rep. 81: 805-814. Rowland, R.E., H.F. Lucas, Jr., and A.F. Stehney. 1977. High radium levels in the water supplies of Illinois and Iowa. In T.L. Cullen and L.P. Franca, eds. Proc. Int. Symp. Areas of High Natural Radioactivity. Academia Brasileira de Ciencias, Rio de Janeiro. Rowland, R.E., H.F. Lucas, Jr., and A.F. Stehney. 1976. Personal communication. Russell, L.B. 1971. Definition of functional units in a small chromosomal segment of the mouse and its use in interpreting the nature of radiation-induced mutations. Mutat. Res. 1 1: 107-123. Searle, A.G. 1974. Mutation induction in mice. Adv. Radiat. Biol. 4:1 3 1-207. Sikov, M.R., and D.D. Mahlum, eds. 1969. Radiation Biology of the Fetal and Juvenile Mammal. AEC Symposium Series no. 17. CONF-690501. U.S. Atomic Energy Commis- sion Sikov, M.R., and D.D. Mahlum. 1972. Plutonium in the developing animal. Health Phys. 22:707-712. Sodd, V.J., R.J. Velten, and E.L. Saenger. 1975. Concentrations of the medically useful radionuclides technetium-99m and iodine-131 at a large metropolitan waste water treatment plant. Health Phys. 28:355-359. Soldat, J.K., N.M. Robinson, and D.A. Baker. 1975. Models and computer codes for evaluating environmental radiation doses. U.S. Atomic Energy Commission Report BNWL-1754 (Feb. 1975, as revised 10/31/75). Soldat, J.K. 1976. Radiation doses from iodine-129 in the environment. Health Physics 30:61-70. Stehney, A.F. 1960. Radioisotopes in the skeleton: Naturally occurring radioisotopes in man. In R.S. Caldecott and L.A. Snyder, eds. Symposium on Radioisotopes in the Biosphere. Center for Continuation Study, University of Minnesota. 366-381. Stehney, A.F., and H.F. Lucas, Jr. 1956. Studies on the radium consent ofhumans ansing from the natural radium of their environment. In Proc. First Int. Conf. on Peaceful Uses of Atomic Energy, United Nations, 11:49-54. Trimble, B.K., and J.H. Doughty. 1974. The amount of hereditary disease in human populations. Ann. Hum. Genet. (Lond.) 38:199-223.

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