By Ross Keller, PhD candidate in Biomedical Sciences

You have probably heard vague notions about the health impacts of radon, but what is it exactly? And how does it impact health?

Currently, radon is believed to be the second leading cause of environmentally caused lung cancer, following smoking. The National Cancer Institute estimates that 15,000-22,000 lung cancer related deaths per year are attributable to radon exposure, with the majority of them occurring in smokers who are also exposed to radon (1).

Radon is radioactive, making it a risk for lung cancer (Pixabay)

Evidence for an increased risk of cancer from radon exposure comes from epidemiological studies as well as animal studies. It was found that occupational exposure to high levels of radon in miners was strongly linked to an increased risk for lung cancer (2). Lower levels of residential radon exposure was also linked to an increased risk in combined analysis of case-control studies in North America (3) and Europe (4). Furthermore, animal studies conducted in the mid-to-late 20^th century clearly demonstrated the ability of radon and its decay elements to cause lung carcinomas (5).

Where does radon come from?

Radon is everywhere—in almost all air, and in fact, we breathe radon with almost every breath. However, it is typically at very very low levels. Radon only becomes a problem when the levels get too high. Higher levels of radon are found in soil and rock because radon is in the radioactive decay chain with a lot of heavy metals (uranium, thorium, polonium…etc—more on that later). When radon is formed in the soil, it can move to the surface as a gas. In nature, this is not much of a problem for animal life because outside air pressure is not low enough to pull a large amount of radon from the soil. However, the air pressure in a typical house is lower than the pressure of the soil and lower than outside air. This makes a house like a vacuum that can pull radon up from the soil and keep it (6).

Once inside, radon will typically sit near the ground because it is 8x heavier than air. This is why radon levels are often tested in the basements of homes. But heating and cooling systems can stir the air, distributing radon around the house.

The EPA recommends that a level of radon inside the house not exceed 4 pCi/L, which stands for picocuries per liter of air (a measure of radiation). If the level exceeds that, it is recommended that steps be taken to seal the house from below and increase ventilation so as to reduce the vacuum effect the house can have on radon.

How can radon increase the risk for lung cancer?

Radon is a colorless, odorless noble gas; it sits very near the bottom of the periodic table and has an atomic number of 86. This means the gas has 86 protons in its nucleus, which are alongside 136 neutrons—making it a very large atom. For comparison, typical gases that we breathe in high volumes are much smaller: an atom of helium has only 2 protons, hydrogen has 1, oxygen has 8, and nitrogen has 7.

Radon (Rn) is in the radioactive decay chain that begins with uranium and contains many heavy metals. Energy is released with each step, sometimes with particles. (Wikimedia)

The large nucleus makes radon unstable, and the instability means it is prone to radioactive decay.  Radioactive decay occurs when an unstable atom spits out energy or even portions of its nucleus in an effort to become stable. The largest known stable element is lead, which has 82 protons and 125 neutrons. For radon (unstable) to become lead (stable) it must shed a total of 4 protons and 11 neutrons, but shedding them means releasing energy and particles in the process.

This is where the problems begin. The particles and energy released need to go somewhere, and if radon is inside the lungs, one of the places it will go is into cells and tissues where it will irritate and cause inflammation—a known cancer risk in itself. Additionally, if the energy penetrates all the way through the cells, it can even hit DNA.

Bombarding DNA with energy can change its chemical makeup. The machinery inside cells are designed to recognize a certain chemical composition of DNA, but if it has been altered by energy during a radioactive decay event, the machinery in the cells will “think” the code is wrong and change it—inadvertently causing a mutation. In addition, if the energy released is particularly high, the energy can actually break a strand of DNA into two, forcing the cell to repair it, sometimes with mistakes, which is a second path to get a mutation caused by radon. And if any of these mutations happen to reside in the wrong portion of a cancer-promoting gene, the cell can begin dividing uncontrollably and eventually develop into a tumor.

Should I get my house tested?

A device will measure the radioactivity that may be present in a home with radon. (Wikimedia)

Radon can occur anywhere, so it’s a good idea to get your home checked. Testing is done on the lowest level of the home over a period of a week for short term exposure, and over a period of a few months for long term exposure. The testing will measure the level of radiation in the air released by the atoms of decaying radon and give a good indication if additional steps should be taken to minimize the amount of radon in the home.

1. Radon and Cancer Fact Sheet. National Cancer Institute. 6 December, 2011. https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/radon/radon-fact-sheet

2. Lubin JH et al. “Radon and Lung Cancer Risk: A Joint Analysis of 11 Underground Miners Studies.” Washington DC: US Department of Health and Human Services; 1994.
3. Krewski, Daniel, et al. “Residential radon and risk of lung cancer: a combined analysis of 7 North American case-control studies.”Epidemiology 2 (2005): 137-145.
4. Darby, Sarah, et al. “Residential radon and lung cancer—detailed results of a collaborative analysis of individual data on 7148 persons with lung cancer and 14 208 persons without lung cancer from 13 epidemiologic studies in Europe.”Scandinavian journal of work, environment & health (2006): 1-84.
5. Masse, R., and AM Kellerer. “Lung Carcinomas in Sprague-Dawley Rats after Exposure to Low Doses of Radon Daughters, Fission Neutrons, or y Rays.”RADIATION RESEARCH 118 (1989): 230-245.
6. Radon in the Home. Center for Disease Control. 13 April 2016. https://www.cdc.gov/nceh/radiation/brochure/profile_radon.htm