RADIUM IN DRINKING WATER
R. E. Rowland
For many years there has been a controversy about radium in drinking water. There are two isotopes of radium that occur in water, Ra-226 and Ra-228; each, at high level can induce bone cancers. The basic question is one of risk; does the presence of these isotopes of radium in drinking water pose a risk to those who drink that water? The answer is easy, yes, there must be some concentration at which radium does become a hazard.
The simple answer is thus obvious, take the radium out of the water. Simple answers, however, are not necessarily the correct answers. For example, what does it cost? When radium is taken out of the water what do you do with it? Typical costs for a community of 25,000 to 50,000 people are $50,000,000 to $70,000,000. Taking radium out of water is equivalent to mining radium, but in this case one ends up with a product for which the is no market. So, in today's world, you ship this unwanted radioactive material to an appropriate storage area. However, instead of this mining taking place at a few locations, it now takes place in thousands of locations, every municipal water department that finds radium in it's water supply. Municipal water departments were set up to provide potable water to citizens, not to become mining companies dealing with the disposal problems of radioactive materials.
Is there perhaps an alternative answer to the problem of radium in drinking water? Yes, there is. Can the risk be evaluated so that one can be sure of its magnitude, and thus set an acceptable level for radium in drinking water? I am convinced that we have all the information we need to adopt a radium level that will provide safe drinking water.
The Environmental Protection Agency (EPA) originally set a level for radium in drinking water, called the Maximum Contaminate Level (MCL), at 5 pCI/L (picoCuries per liter) in 1976. This has been reviewed several times. Perhaps the most interesting review occurred in 1991, when the EPA published in the Federal Register1 a proposed new MCL, namely 20 pCi/L for Ra-226 and 20 pCi/L for Ra-228. This proposed MCL was potentially eight times greater than the original level, allowing a total of 40 pCi/L of radium in drinking water instead of a total of 5 pCi/L. This was, unfortunately, never adopted, but illustrates the awareness of the EPA scientific staff that there was no valid reason for the MCL to be set as low as 5 pCi/L.
The very fact that there are regions in our country where radium occurs in the water supplies comes as a surprise to most citizens. It shouldn't be, for there is a lot of radium in our environment, rather uniformly distributed. For example, soil, the dirt in your yard and garden contains quite a little radium2. Using the same units as for drinking water, typical soil contains radium within a concentration range of 900 to 1800 pCi/L. Since water for most communities comes from the soil, perhaps one should not be surprised that it contains some radium; the surprise may be that it contains as little as it does.
Since soil contains radium it should also not come as a surprise that most plants grown in soil contain radium, and thus all food products contain radium. It has been estimated that the daily per person ingestion of radium from food in the United States is 2.4 pCi3 (1.4 pCi of Ra-226 and 1 pCi of Ra-228). Thus all of us, all over the world, contain radium within our bodies.
How much radium do we carry in our bodies? A number of laboratories in our country have made measurements of the radium body content of randomly selected individuals: listed here are brief summaries of results from four such studies.
New York City4: 53 cases: average = 77.8 pCi: range 28.0 to 255 pCi.
San Francisco4: 42 adults: average = 59.2 pCi: range 10.4 to 364 pCi.
Illinois5: 126 cases: average = 87.9 pCi: range 13.3 to 572 pCi.
Pacific Northwest6: 50 cases: average = 45.4 pCi: range 12 to 139 pCi.
As might be expected, there is quite a range of values.
What is the risk to an individual of these various levels of radium in the body? The EPA looks to the results of the atomic bombs dropped upon Japan to determine the risk. Of course the atomic bomb irradiated the exposed population with a massive flood of gamma rays and neutrons which lasted only a few seconds; how does this compare with exposure to radium? Each radium atom deposited within the body (mostly in bone, because radium atoms in the body are handled as if they were calcium atoms) slowly are changed into other radioactive atoms by the process of radioactive decay. In the case of Ra-226 atoms half of them decay within 1600 years, while the atoms of Ra-228 decay much faster, for its half-life is only 6.8 years.
Many of us feel that the atomic bomb, with its instantaneous flood of radiation, is not a valid model from which to predict the effects of slowly decaying radioactive atoms within the human body. Instead, we suggest that the study of radium in humans, funded for almost half a century by federal agencies, should be the source for valid estimates of risk for radium. These studies were started by the individual physicians who first examined the radium dial painters in the late 1920s, were further extended by the Atomic Energy Commission when the decision to build the atomic bomb was made, and were maintained by successor agencies to the Atomic Energy Commission until the late 1980s. When these studies were terminated there were still over 1000 living people with known levels of radium in their bodies that had been followed by the radium program. A brief history of this program and its findings may be found at Dial Painters.
It is clear from this large and long study of the radium cases that no detectable effects from injected or ingested radium were ever seen when the quantity of radium that entered the human body was less than 100 µCi. It is appropriate here to digress; what is the Curie? The Curie was originally defined as the rate of decay of one gram of Ra-226, and subsequently precisely defined as 3.7 x 1010 disintegration per second, or 37,000,000,000 disintegrations per second. This is a very large number, and since one usually works with smaller quantities, quantities such as one millionth of a Curie, abbreviated as µCi, and one millionth of a µCi, the pCi, are the units most often seen. The picoCurie, pCi, has a decay rate of 0.037 disintegrations per second, or about 2.2 d/m.
The EPA calculates the daily intake of radium from drinking water to be that contained in 1.1 liters of water1. It recognizes that only 20% of the ingested radium is absorbed from the gut and enters the body's circulatory system; the other 80% is eliminated with the fecal matter. Thus one is going to need to ingest a lot of water in order to bring the body content anywhere near the level at which malignancies due to radium appear.
I have long argued that a reasonable MCL for the radium isotopes in drinking water should be set at 20 pCi/l. Most water used for drinking in the United States contains less than 20 pCi/L, so this level would mean that most of the thousands of communities that are struggling to remove radium would see their problem disappear. Further, most of the problems of getting rid of the radium removed from water would likewise disappear.
If a reasonable solution not found soon we will eventually have a much greater problem in the future; how to we get rid of the radium that will be extracted from the water? I would venture to predict that the radium problem will grow into nightmare for the regulatory agencies as they desperately look for some face saving way to push this monumental mistake "under the rug".
The superscripted references in the above text are listed below:
1. Federal Register (1991). National Primary Drinking Water Regulations; Radionuclides; Proposed Rules. Vol. 56, No. 138, pp. 33050-33127.
2. NCRP 77 (1984). Exposure from the Uranium Series with Emphasis on Radon and its Daughters. National Council on Radiation Protection and Measurement Publication Bethesda, MD.
3. NCRP 94 (1987).. Exposure of the Population in the United States and Canada from Natural Background Radiation. National Council on Radiation Protection and Measurement Publication, Bethesda, MD.
4. Hallden, Fisenne,& Harley. Intake and Retention of Radium at Natural Levels. Science, 140 pp. 1327-1328, (1963)
5. Holtzman. .Measurement of the Natural Contents of RaD (Pb210) and RaF (Po210) in Human Bone - Estimates of Whole-Body Burdens. Health Physics 9, 385-400 (1963)
6. Palmer & Queen. Hanford Publication HW-31242 (1956).