Water can be radioactive due to the presence of unstable atoms, known as radionuclides, that release energy through decay. This radioactivity is undetectable without specialized testing, as it does not affect the water’s taste, smell, or appearance. Radionuclides enter water supplies through both natural geological processes and various human activities. Understanding the source and nature of this radiation is the first step toward managing potential public health risks.
The Mechanism of Radioactive Water Contamination
Water becomes contaminated through two main pathways: the natural environment and human-made sources. The most widespread source is geological leaching, occurring when groundwater flows through rock and soil formations containing naturally radioactive minerals. These minerals, primarily uranium and thorium, break down, releasing decay products like radium into the water supply.
Groundwater is particularly susceptible because prolonged contact with bedrock allows for the dissolution of radionuclides. Radon, an odorless gas produced by radium decay, can also dissolve directly into groundwater, especially in private wells.
Human activities contribute artificial radionuclides or enhance the mobilization of natural ones. Anthropogenic sources include waste discharge from nuclear power plants and medical facilities that use radioisotopes. Mining activities, particularly for uranium and phosphate, can expose and concentrate naturally occurring radioactive material, releasing it into surface and ground waters. Atmospheric fallout from historical nuclear weapons testing also contributes long-lived radionuclides to the environment.
Key Radionuclides Commonly Found in Water
Several specific radionuclides are frequently detected in drinking water, each having a distinct origin and behavior. Radon, a noble gas, is one of the most common and is primarily found in well water drawn from fractured bedrock. As a decay product of uranium and radium, it readily dissolves into the water before escaping into the air during use.
Uranium is a naturally occurring metal whose presence in water poses a dual threat: radiological toxicity from its decay and chemical toxicity that can damage the kidneys. Radium, another natural decay product, is a bone-seeking element that chemically mimics calcium. This allows it to be easily incorporated into the human skeleton upon ingestion.
Artificial radionuclides are also a concern, such as Tritium, a low-energy beta emitter and a byproduct of nuclear reactor operations. Tritium is often released as a tracer because it readily incorporates into the water molecule itself. Strontium-90, created during nuclear fission, also mimics calcium and can accumulate in bone tissue.
Assessing the Safety of Water
Water safety is assessed by measuring its radioactivity, which reflects the rate at which radionuclides decay. The international standard unit for measuring this activity is the Becquerel (Bq), representing one disintegration per second. In the United States, the unit most commonly used is the picocurie per liter (pCi/L).
These measurements indicate the concentration of radiation, not the total mass of the material. Governing bodies establish Maximum Contaminant Levels (MCLs) for radionuclides to limit potential long-term health risks. For example, the MCL for the combination of Radium-226 and Radium-228 is set at 5 pCi/L.
Public water systems must conduct regular laboratory testing to ensure compliance with regulatory standards. Private well owners are responsible for their own water quality and must proactively seek laboratory analysis. The results of these tests allow consumers and regulators to determine if protective measures are necessary.
Health Effects and Water Treatment
The primary health risk from radioactive water is internal exposure from ingesting the radionuclides, not external exposure. Once consumed, these elements are absorbed into the bloodstream and accumulate in specific organs, where they continuously emit radiation. This internal radiation can damage cellular DNA, increasing the lifetime risk of developing cancers, particularly of the bone, kidney, and bladder.
Uranium is known to cause chemical damage to the kidneys, while radionuclides like Radium and Strontium-90 target bone tissue. Chronic exposure to low levels of radiation over many years is the main concern, rather than acute effects from a high dose. Effective water treatment is necessary to mitigate these dangers.
Water Treatment Methods
Several treatment technologies are highly effective at removing radionuclides from water. Reverse osmosis systems force water through a semipermeable membrane that blocks the radioactive ions, achieving elimination efficiencies up to 99%. Ion exchange units can also be used, swapping radionuclides for non-radioactive ions, similar to a water softener. For the gaseous contaminant Radon, aeration systems can be installed to strip the gas from the water before distribution.