Radon

Radon is a naturally occurring radioactive, colorless, odorless gas. It is the leading cause of lung cancer in 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 320 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 10.20).

Figure 10.20: Radon zone map of the US. (Note: Zone 1 contains the highest radon levels.)

Figure 10.20: Radon zone map of the US. (Note: Zone 1 contains the highest radon levels.)

In the South Central US, the highest radon concentrations are generally associated with black, organic-rich Pennsylvanian shales in northeastern Kansas and the northwest corner of Missouri, and black Cretaceous shales in north-central Kansas. Radon risk in western Kansas is associated with Neogene sandstones containing volcanic ash layers. (Figure 10.21). Volcanic ash can be high in uranium that eventually decays to radon. Water moving through the ash into the surrounding sandy layers carried with it uranium-rich dissolved silica that precipitated between the grains of the sandstone.

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.

Figure 10.21: Radon risk levels at the surface in the South Central US.

Figure 10.21: Radon risk levels at the surface in the South Central US.