What is the primary exposure route for radon in drinking water?

• A. radon gas is emitted from treated water when used in showers, bathing, and other in home activities
• B. radon gas is emitted from untreated groundwater when used in showers, bathing, and other in home activities
• C. particulate radon is ingested by drinking groundwater
• D. radon is ingested from eating foods grown in radon-containing soil

Answer: (B)

Radon exposure from drinking water mainly comes from inhaling the gas that escapes from groundwater into indoor air during household water use. When hot water is used—showering, bathing, etc.—radon dissolved in the water off-gasses and is inhaled, delivering most of the radiation dose to the lungs. Drinking the water itself contributes far less to overall exposure, and while groundwater may contain radon before any treatment, it is the release into indoor air during use that makes inhalation the primary route.