National Water-Quality Assessment (NAWQA) Program

What is radium?

Radium is a naturally occurring radioactive element (or radionuclide) that generally is present at low levels in all soil, water, and rocks. It is derived from the decay of the common and long-lived radioactive elements uranium and thorium. Three commonly occurring isotopes of radium are radium-224, radium-226, and radium-228 (abbreviated as Ra-224, Ra-226, and Ra-228, respectively). Each radium isotope varies in abundance because each decays at a different rate (known as a “half-life”) to a daughter product or progeny (a different element). Radium-226 is the most abundant radium isotope in the environment, primarily because of its long half-life (about 1622 years). Ra-228 has a half-life of slightly less than 6 years, and Ra-224 has a very short half-life (less than 4 days). When Ra-228 decays, it gives off a beta particle (an electron). When Ra-224 and Ra-226 decay, they give off an alpha particle (a helium nucleus). All radium isotopes can contribute to the total amount of radioactivity in a water sample. This total level of radioactivity, measured as gross alpha-particle or beta-particle activity, often is used as a cost-effective screening tool to determine the general presence of many different types of radionuclides in water samples.

How does radium get from rocks into groundwater?

Most rocks and sediment contain some uranium and thorium and, thereby, contain radium as well, but usually in small quantities. Uranium and thorium are most common in granitic and metamorphic crystalline rocks and in associated weathered sedimentary deposits in the central United States and mountainous regions of the East and West. Groundwater slowly flows through pores, aquifer sediments, or cracks in underground rocks and dissolves radium-bearing minerals as it moves. Chemical processes in groundwater and on rock surfaces, such as mineral dissolution, desorption, and ion-exchange reactions, control the release of radium from aquifer solids. Radium also can be physically pushed into pore water during isotope decay.

What human-health concerns are related to radium?

Exposure to radium over long periods of time can increase the risk of cancer. Radium can enter the body in drinking water, food, or inhaled dust particles that contain radium. It can be stored in the body because it behaves similarly to calcium and can replace calcium in tissues, particularly bone. Long-term internal exposure to radium increases the risk of developing diseases such as bone and sinus cancer, lymphoma, and leukemia. Because radium readily accumulates in the body, it is considered to pose a greater cancer risk than most other radioactive elements. Radiation exposure from radium received externally through washing, showering, or other uses of water is less of a concern since human skin tends to block exposure to alpha radiation and minimize penetration of beta radiation.

What is the maximum contaminant level (MCL) for radium in drinking water?

The USEPA has established a Maximum Contaminant Level (MCL) in drinking water of 5 picocuries per liter (pCi/L) for combined radium (defined as the sum of the concentration of Ra-226 and Ra-228). The MCL is based on an accumulated lifetime (70 years) risk from drinking 2 liters of radium contaminated water per day. Although not a requirement, the USEPA encourages public water-supply systems to perform sampling and analysis for Ra-224, because this radium isotope can contribute substantially to gross alpha-particle activity in some locations. The USEPA has established an MCL for gross-alpha particle activity of 15 pCi/L (not including the activity from radon and uranium). Ra-224 is one of many radionuclide alpha emitters that contribute to the gross alpha measurement. Because Ra-224 has such a short half life, it is recommended that sampling and analysis be conducted within 48 to 72 hours in areas where Ra-224 is expected to be present. Studies by USEPA and USGS have been working to define these radium-rich areas.

What is picocurie per liter?

A picocurie per liter is a measure of the number of radioactive decays per minute in one liter of water. One picocurie equals 2.2 radioactive disintegrations per minute.

What is an MCL?

A maximum contaminant level (MCL) is a legally enforceable USEPA drinking-water standard. It sets the maximum permissible level of a contaminant in water that is delivered to users of a public water system that provides water for human consumption through at least 15 service connections or regularly serves at least 25 individuals. The USEPA sets MCLs as close as is feasible to the maximum contaminant level goal (MCLG), which is the maximum level of a contaminant in drinking water that has an adequate margin of safety and has not been shown or proved to cause adverse health effects. When establishing MCLs, the USEPA takes into account the best available analytical and treatment technologies and cost considerations. The MCL for combined radium applies to the finished drinking water provided by public water systems (after treatment and before distribution). In this study, radium concentrations in untreated source water for public-supply wells and private (domestic) wells were compared to the MCLs to provide an initial perspective on the potential significance of detected contaminants to human health. Concentrations measured in source water do not necessarily reflect the quality of finished water from public water systems.

How do the study results compare to the MCL?

Although radium isotopes were present in raw water from sampled wells tapping every principal aquifer, the combined radium concentration generally was below the established MCL. Overall, few sampled wells (about 3.2 percent, or 40 of 1,266 wells) contained individual concentrations or combined concentrations of Ra-226 and Ra-228 greater than the MCL. Of the 15 principal aquifers studied, 7 had combined radium concentrations in at least one well that were greater than the MCL. Two principal aquifers, the Mid-Continent and Ozark Plateau Cambro-Ordovician and the Northern Atlantic Coastal Plain aquifer systems, had detections of combined radium at levels above the MCL much more frequently than the other aquifers. Both these aquifers are composed of materials low in uranium and thorium, the parent compounds for radium, which indicates that other factors, such as geochemistry, are important relative to the variability of concentrations of radium in the water.

What if I have radium in my drinking water?

A number of treatment options are available to public water suppliers and homeowners for removing radium from drinking water. One cost effective method for homeowners is the use of water softeners, which can remove radium from water (in addition to calcium and magnesium). Reverse osmosis systems also can be used to remove radium; however, this type of treatment system can produce only small volumes of treated water and usually just supplies a single source, like the kitchen sink, not the whole house. Public water supplies have many other choices for treating the water to remove radium, including ion exchange, iron removal, and lime softening, among others. Information on compliance options for public suppliers can be found at: http://water.epa.gov/lawsregs/rulesregs/sdwa/radionuclides/compliancehelp.cfm. Public water suppliers and private homeowners can contact the National Sanitation Foundation (http://www.nsf.org) and the Water Quality Association (http://www.wqa.org) for assistance in determining the best treatment options for radium. In addition, the National Ground Water Association (http://www.ngwa.org) is dedicated to education efforts aimed at reducing contaminant risks to water supplies and provides a summary of treatment considerations and an overview of strategies for well owners.

What three water types are likely to contain radium?

Three geochemical conditions were associated with elevated concentrations of radium in groundwater. These include 1) low levels of dissolved oxygen (dissolved oxygen less than 1 milligram per liter, fig 2), 2) acidic water (pH less than 6, fig 3), and 3) water with high concentrations of dissolved solids (especially calcium, barium, magnesium, strontium, potassium, sulfate, or bicarbonate). These water conditions can prevent radium from sticking to aquifer sediments (adsorbing) and increase its solubility in groundwater. Low-oxygen conditions were most prevalent nationally and explained the occurrence of high concentrations of radium in more principal aquifers than the other two water conditions.

Which principal aquifers are most vulnerable to radium contamination?

The greatest frequency of elevated radium in groundwater is found primarily in the eastern and central United States (fig. 1). About 98 percent of the sampled wells that had combined radium concentrations greater than the MCL were located east of the High Plains. More than 20 percent of wells sampled in the Northern Atlantic Coastal Plain and Mid-Continent and Ozark Plateau Cambro-Ordovician aquifer systems had combined radium concentrations greater than or equal to the MCL. Among the remaining five principal aquifers with elevated radium concentrations, the Floridan aquifer system had the greatest frequency of sampled wells with combined radium concentrations greater than the MCL, followed by the granitic and metamorphic crystalline-rocks of the New England province, the Mesozoic sedimentary basins in or adjoining the Appalachian Piedmont, the Gulf Coast Coastal Plain aquifer systems, and glacial deposits.

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U.S. Department of the Interior | U.S. Geological Survey
URL: http://water.usgs.gov/nawqa/trace/radium/Ra_FAQ.html
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Page Last Modified: Wednesday, 09-Jan-2013 12:02:10 EST