Radon

Radon is a naturally occurring radioactive, colorless, odorless gas. It is the leading cause of lung cancer in American non-smokers, and the second leading cause of lung cancer overall. It can collect in homes, buildings, and even in the water supply. Radon gas is formed naturally when uranium-238 undergoes radioactive decay, producing energy and several radioactive products such as radon-222 and thorium-232. (The thorium later decays to emit energy and radon-220.) Radon is more commonly found where uranium is relatively abundant in bedrock at the surface, often in granite, shale, and limestone. The EPA produced a map of the US showing geographic variation in radon concentrations, divided into three levels of risk: low, medium, and high (Figure 10.21).

Figure 10.21: Radon zone map of the US. (Note: Zone 1 contains the highest radon levels.)

Radon concentrations are generally high throughout the Northwest Central US (Figure 10.22). Uranium is relatively concentrated in the granites and metamorphic rocks of the Rocky Mountains, Black Hills, and Basin and Range, as well as in the sediments eroded from these areas. Uranium is also concentrated in some Paleogene sandstones and coal deposits. Taken together, these areas account for a broad part of the Northwest Central. There are, however, areas that are moderate or low in radon—the Sandhills of northwest Nebraska have the lowest radon concentrations in the Northwest Central. This area is composed of windblown sediment that was separated from the clay and heavier minerals that contain relatively high amounts of uranium. In the Columbia Plateau, radon associated with basalt bedrock is also lower in concentration than that found in the mountains farther north.

Figure 10.22: Radon risk levels at the surface in the Northwest Central US.

Radon is chemically inert, meaning that it does not react or combine with elements in the ground, and it can move up through rocks and soil into the atmosphere. It is dangerous primarily when it accumulates indoors, creating a health hazard similar to that of secondhand smoke. Radon gas finds its way through cracks in basement foundations, sump pump wells, dirt floor crawlspaces, and basement floor drains. It can also be found in well and municipal water. Since radon is more easily released from warm water than from cold water, one of the greatest forms of exposure likely occurs while showering in water with high radon levels.

Radon cannot be detected by sight or smell, so there is no way that the body can sense its presence. Fortunately, with proper monitoring and mitigation (reduction) techniques, radon gas can be easily reduced to low levels. One technique that is often used in homes involves sealing cracks in the basement floor, covering drains, and installing ventilation systems. A well-ventilated space will prevent the radon from accumulating and will reduce the risk of exposure. Most states have licensed radon mitigation specialists who are trained in the proper testing and mitigation of radon levels in buildings. The EPA has also published a homebuyer’s guide designed to help citizens make informed decisions about radon gas. For radon in water, filtration systems can be installed to mitigate exposure in the home.