What is radon?

Radon is a radioactive gas that forms from the natural decay of the element uranium. Because uranium is found in all soils, radon gas is emitted virtually everywhere. It is odorless, colorless, and completely undetectable without the right equipment. It travels upwards through cracks in the underlying rock and, eventually, into homes and buildings. If such structures are poorly ventilated, radon can gradually accumulate to unsafe levels.

Why is radon important?

Exposure to radon greatly increases the risk of various types of cancer, with lung cancer at the top of the list. When radon is inhaled over a long period of time, the alpha radiation that is emitted during the decaying process greatly damages the lung cells. The United States Environmental Protection Agency (USEPA) estimates that radon causes more than 20,000 deaths from lung cancer each year in the United States. It is the leading cause of lung cancer among non-smokers, and the second leading cause among smokers.

How is radon measured?

Indoor air is often used to measure human exposure to radon gas, as it offers a controlled environment for testing. It is also where radon accumulates the most. It is measured in picocuries per liter of air, or pCi/L. USEPA prescribes a maximum reading, or “action guideline level”, of 4 pCi/L for safe levels of radon in indoor air. Any building or household measuring above 4pCi/L is deemed unsafe. The Guam Environmental Protection Agency (Guam EPA) Radon Lab currently uses activated charcoal canisters to measure indoor radon (Figure 1).

The canisters are opened, and then exposed to ambient air for a certain period of time. The charcoal becomes saturated with radon gas, which is then measured using gamma ray technology (Figure 2).

Guam’s Current Radon Levels Historically, Guam’s indoor radon levels have exceeded the USEPA maximum standard of 4pCi/L in almost 40 percent of tested buildings.

A study performed by Denton and Namazi in 2013 estimated a weighted average (an average that is scaled by importance) for villages in the northern half of Guam that ranged from 2.4 pCi/L to 17.3 pCi/L, while the weighted average for villages in the southern half ranged from 0.3 pCi/L to 3.2pCi/L. A separate study, performed by Burkhart et al. in 1993, found that one building measured as high as 143 pCi/L.

Radon and Guam’s geology

Past studies have found possible relationships between Guam’s unique geology and its corresponding radon levels. The northern to central half of Guam is dominated by limestone bedrock, while the southern half consists mainly of volcanic rock. Structures located directly above the limestone formations measured well above 4 pCi/L, while structures located above the volcanic formations measured relatively low.

It is assumed that because the northern limestone is more porous than the southern volcanic rock, radon travels through cracks easier and accumulates in buildings at a faster rate. Radon movement in buildings is driven by soil pressure, rather than the pressure found within the building itself. Because moisture and wind affect pressure, indoor radon concentrations are significantly greater during the rainy season.

Radon and Guam’s lung cancer rates

Of the few studies that have focused on the relationship between Guam’s indoor radon levels and Guam’s lung cancer rates, an apparent correlation has yet to be established. Studies on the high radon levels of the northern villages and the lung cancer rates recorded within these villages show that northern villagers actually have lower lung cancer rates than their southern counterparts. Considering other variables, such as ethnicities and smoking habits, the study concluded that the high radon levels in the north did not necessarily lead to higher instances of lung cancer in those areas.

However, the findings of the study do not discredit radon’s harmful effects entirely. Historically, radon has been understood as a viable presence that contributes to the overall domino effect of cancer development. The damage that extended exposure to radon can cause to lung cells has long since been recognized. Numerous studies around the world have found correlations between radon and lung cancer rates, with various variables, such as smoking habits and geology, considered.

Given the high levels of radon that have been recorded on Guam in the past, more in-depth research is necessary to determine any possible relationships involving radon and the island’s cancer rates.

Recommendations for Guam residents

Globally, radon has proven to be the cause of various adverse health effects, with lung cancer at the forefront. As Guam has historically measured high levels of radon in private homes, and even schools, mitigation practices are highly recommended for any resident wanting to feel safe from radon’s potentially harmful reach. These practices can range from regularly opening windows and doors for better circulation to installing expensive piping throughout the foundation. Further information on radon exposure and mitigation can be found online at USEPA’s website: A Citizen’s Guide to Radon.

Becoming informed is an important first step in protecting oneself and one’s family from radon’s impacts. Reducing radon’s possible harmful effects on the island can only be achieved through public awareness.

About the author

Hanna Jugo was a University of San Diego graduate with a Bachelor of Arts in Environmental Studies. She was attending the University of Guam as a pre-candidate graduate student in the Sustainable Agriculture, Food, and Natural Resources (SAFNR) Graduate Program. She wa also employed at the Guam Environmental Protection Agency (Guam EPA) as an Environmental Health Specialist in the Air Pollution Control (APC) Program. Her interests include environmental sustainability that allows for social progress.

Editor’s note: This author was a beginning graduate student in 2018 taking a course in scientific writing at the University of Guam. This article was assigned to provide the student with practice in communicating science to non-scientists. The student chose the topic  which is related either to their thesis project or work experience. The instructor in the course is Dr. Laurie Raymundo, a UOG Marine Laboratory faculty member.

For further reading

Burkhar, James F., D. Kladder, and F. Castro. “Radon Distribution On The Island of Guam and Correlations to Surficial Geology and Deposition Models.” Proceedings of the AARST 1993 International Radon Conference, Denver, Colorado, September 1993.

Denton, Gary R.W., and Sara Namazi. “Indoor Radon Levels and Lung Cancer Incidence on Guam.” Procedia Environmental Sciences 18, (2013): 157-166.

Gundersen, Linda CS, R. Randall Schumann, James K. Otton, Russell F. Dubiel, Douglass E. Owen, and Kendell A. Dickinson. “Geology of Radon in the United States.” In Geologic Controls on Radon, edited by Alexander E. Gates and Linda C.S. Gundersen. Boulder: Geological Society of America, 1992.

Kladder, Douglas L., James F. Burkhart, Mark S. Thorburn, and Parter Q. Cruz. “An Investigation of Factors Affecting the Entry of Radon into Structures on the Island of Guam.” Environment International 22, no. 1 (1996): 454-555.

US Environmental Protection Agency. Basic Radon Facts. Washington, DC: EPA, 2016.