Radionuclides contaminating water is a developing issue. Radioactivity in ground water formerly was limited to natural causes such as radon, radium, or uranium. But releases from nuclear power plants and medical facilities have added the dimension of man-made radioactivity finding its way into drinking water sources. What follows are answers to frequently asked questions about radionuclides:
It is a radioactive chemical that is found in water. It is usually, but not always, naturally occurring.
The most common are radon, radium, uranium, gross alpha, and beta and photon emitters.
- Radon is a naturally occurring gas that emits ionizing radiation. It can be found in several places. In fact, the U.S. Environmental Protection Agency (EPA) recommends testing for radon in homes and apartments below the third floor.
- Radium-226 and radium-228 are naturally occurring. They are ground water contaminants that arise at trace levels.
- Uranium is a naturally occurring contaminant that is found in ground water and surface water.
- Alpha emitters usually occur naturally, but several can come from man-made sources. They can occur in ground water and surface water.
- Beta and photon emitters are primarily man-made and associated with nuclear power plants, facilities that use radioactive material for research or manufacturing, or establishments that dispose of radioactive material. They occur primarily in surface water. Some beta emitters can occur naturally.
Radionuclides occur naturally as trace elements in rocks and soils as a consequence of the radioactive decay of uranium-238 and thorium-232. It happens because radioactive atoms have too much energy, and they release or transfer that energy. The released energy is called ionizing radiation. It can be alpha particles, beta particles, or gamma rays.
Exposure to ionizing radiation can lead to several types of cancer, and extremely high doses of radiation can cause death.
Radon can cause lung cancer, and drinking affected water can lead to stomach cancer. High exposure to radium-226 and radium-228 has been known to cause bone, stomach, lung, and other forms of cancer. Uranium is believed to cause bone cancer, and the EPA has stated it can be toxic to kidneys too. Gross alpha, beta, and photon emitters are considered carcinogens as well.
By far, the best solution is isolation of a radionuclide source from the water supply. For example, uranium is often associated with shale in sedimentary rock in discrete layers. In some situations, the unit (detectable by analyzing drill cuttings or borehole geophysical logs) can be sealed off with casing and grout.
Among the different types of technologies that treat radionuclides are co-precipitation with barium sulfate, greensand filtration, ion exchange, lime softening, preformed hydrous manganese oxide filtration, and reverse osmosis. Radon is effectively removed by ventilation (see radon section).
Whether or not a particular treatment removes radionuclides from drinking water effectively depends on the contaminant’s chemical and physical characteristics, as well as the water system’s characteristics such as size and water quality.
- Co-precipitation with a barium sulfate is the process of adding a soluble barium salt to radium-contaminated water. It is mainly used in waste water. Data have shown success in removing 95% of the radium.
- Greensand filtration consists of a filter box with manganese greensand replacing the traditional filtration medium. Studies have indicated the sand removes up to 56% of the radium.
- Ion exchange can be used on small systems. It removes 90% of the radionuclides it encounters. The water flow must be regularly monitored, and the resin must be regenerated frequently. Attention must be given to disposal of the brine regeneration wastewater stream, that may contain elevated levels of radionuclide.
- Lime softening can be used to remove radium. It has an efficiency of 80% to 95%. Adding lime to water increases its pH, and can also be a method for treating hard water. This is most often used in public water supply, and resulting lime solids may also have elevated radioactivity.
- Preformed hydrous manganese oxide filtration is a method for radium-contaminated water. It is fairly inexpensive if filters are already in place. It requires proper dosages, and if water quality varies, the dosage must be recalibrated.
- For radon coming primarily from insoluble radioactive minerals in aquifers, especially igneous and metamorphic rock, the gaseous radon is usually removed by active ventilation. Ventilation exhaust should be directed away from human or animal residences.
- Reverse osmosis removes multiple radionuclides, including radium and uranium. It can have a success rate up to 98%. Concentrate streams may have elevated radioactive content and should be managed accordingly.
For all these technologies, waste streams (even ventilation of radon) may be excessively radioactive. There is no “away” that should be ignored.
Treatment technologies must be designed and maintained by professionals familiar with the work. Local health professionals and hydrogeologists will be familiar with the occurrence of radioactivity in natural formations and water. Qualified water well contractors may know about formation sequences associated with radioactivity. If radioactivity is due to contamination incidents such as military, power plant or mining activity, resolution is beyond local action. However, if removal is unlikely, treatment is needed.