It is widely known that breathing radon in the indoor air of homes is a public health risk. In 1998, the National Academy of Sciences (NAS) reported that radon is the second leading cause of lung cancer in the U.S., after smoking, causing about 15,000 lung cancer deaths per year.
Radon is a radioactive gas occurring naturally in the environment. It is produced by the breakdown of uranium in soil and rock. Radon gas, moving through the soil, enters buildings through cracks and holes in the foundation. However, when radon is released in the ground, it can also dissolve and accumulate in groundwater, such as well water, and affect drinking water supplies. Radon gas easily escapes from water once the water is exposed to air. Radon gas is released into the indoor air of a home by simply running the water for household purposes.
While the risk of radon entering homes through water is small compared with that of radon entering through the soil, the gas released from the water will contribute to the total indoor air concentration. About 1-2% of the radon in indoor air comes from drinking water.
Some radon will also stay in the water and an additional cancer risk comes from drinking water containing dissolved radon. Based on a second NAS report (EPA server), the U.S. Environmental Protection Agency (EPA) estimates that radon in drinking water causes about 168 cancer deaths per year, 89 percent from lung cancer caused by breathing radon released from water, and 11 percent from stomach cancer caused by drinking water containing radon.
These numbers may not indicate as high a risk when compared to breathing radon gas. However, there is a 100 -10,000 times greater risk of developing cancer from household use and consumption of water containing
high levels of radon compared to the cancer risk from other contaminants in drinking water.
Congress passed the Safe Drinking Water Act (SWDA) in 1974 to protect public drinking water supplies from harmful contaminants. In 1996, extensive amendments to the Act contain a mandate for the EPA to issue drinking water regulations, including the control of radon. The Congressional Research Service Issue Brief for Congress, Safe Drinking Water Act: Implementation and Reauthorization (December 3, 1996) discusses the 1996 amendments to strengthen standard-setting procedures, enforce authority, and provide groundwater protection provisions.
In October 1999, as required by the SWDA, the EPA has developed a proposed regulation to reduce radon in drinking water. The Federal Register Notice for the proposed Radon in Drinking Water Rule can be viewed at (EPA server): Part 1 |
Part 2 |
The proposed standards would apply to community water systems that use ground water or mixed ground and surface water, excluding private wells. In general, radon is not a concern with public drinking water systems, where the radon can be released to outdoor air before reaching the home. The proposal offers the states and individual water systems two options for reducing public health risks from radon in both drinking water and indoor air. The most cost-effective option is to develop state programs to address the health risks from radon in indoor air, while individual water systems reduce radon levels in drinking water to 4,000
pCi/L or lower.
The second option is that individual water systems in a state would be required to either reduce radon in their system's drinking water to 300 pCi/L or develop an individual local program to address indoor air while reducing radon levels in drinking water to 4,000 pCi/L or lower. The proposal provides states flexibility in how to limit exposure to radon by allowing them to reduce the risks from radon in drinking water, while also focusing their efforts on the radon risks from indoor air, a much greater threat.
Written by Amy L.