Radon is a radioactive gas released as uranium in rock and soil breaks down. It has no color, smell, or taste. Indoors it collects on lower levels, and long exposure raises lung cancer risk. The only way to know your level is to test.
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In Central Ohio the uranium comes mostly from the Devonian Ohio Shale, which the USGS describes as averaging about 30 parts per million uranium and as the largest uranium source in the state, and from soils weathered out of the Columbus and Delaware limestones. Radon moves through soil as a gas and follows the easiest path, including up through a foundation. Its short-lived decay products do the damage: breathed in, they lodge in lung tissue. The EPA estimates about 21,000 radon-related lung cancer deaths in the United States each year. For scale, outdoor air averages about 0.4 pCi/L and indoor air about 1.3 pCi/L nationally, and the EPA recommends fixing a home at 4 pCi/L or more. See why Central Ohio runs high.