... And its leading water pollutant.

. . . and its leading water pollutant

The radon seeping out of rock often collects in groundwater used to supply drinking water. EPA data indicate that about 20,000 U.S. groundwater supplies--roughly 40 percent of the public drinking-water supplies--contain 200 to 600 pCi/l of radon, according to a report by the agency's C. Richard Cothern and Edward V. Ohanian. Though a far less serious risk than the radon seeping through the soil, this source of the pollutant is still estimated to contribute 30 to 600 excess lung-cancer deaths annually in the United States, they note. Paul Milvy, in EPA's Office of Drinking Water, says that makes radon his agency's leading drinking-water risk.

The health risk from radon in water is not so much from drinking it as from inhaling it during showers, bathing, cooking, washing and the flushing of toilets. As a general rule of thumb, says Sheldon Meyers, director of EPA's Office of Radiation Programs, 10,000 pCi/l of radon in water will be responsible for 1 pCi/l of radon in indoor air.

Last Sept. 30, EPA announced its intent to set limits on radon in public drinking-water supplies. Milvy says the proposed limit--expected to be announced by next Jan. 1--will probably fall between 500 and 5,000 pCi/l. Under such a limit, Cothern and Ohanian say, radon could convey a higher allowable health risk than any other controlled drinking-water pollutant. Most toxic chemicals, for example, are controlled to limits providing just a 1-in-100,000 or 1-in-1-million risk of causing a fatal cancer. The lower limits being considered for radon offer a 1-in-10,000 lifetime risk of dying from lung cancer, according to Cothern and Ohanian, who presented their findings recently at the Health Physics Society annual meeting in Salt Lake City.