Invisible: Radon Gas at the Pinenut Uranium Mine

Arizona, USA, 2015-16

Katherine Walton-Day, JoAnna R. Wendel, Jo Ellen Hinck, David L. Naftz, and Sharon L. Qi

January 15, 2021

Photo of the view looking south over Kanab Canyon, near the Grand Canyon, AZ.

Graphic panel showing a drawing of an aerial view of the location of the Pinenut Mine. It is just north of the Grand Canyon, produced 1.4 million pounds of uranium oxide since the 1980s and ended operation in 2016. Reclamation of most of the mine site was conducted from 2018 to 2019.

Graphic panel showing a drawing of a bulldozer pushing dirt and hands planting plants representing mine reclamation activities, which include planting vegetation and removing waste rock and buildings from the surface. Before reclamation began, all mining ceased, and all ore was removed for processing.

Graphic panel showing a drawing of radon gas escaping from rock piles of mine waste that were present during mine operations. The concern is that decaying uranium at similar mines will produce elevated or potentially harmful levels of radon gas.

Graphic panel showing a drawing of the uranium parent atom and how it decays into daughter atoms. Radon is a product of uranium decay. Decay of a radioactive molecule to a daughter molecule produces a stream of electrons or an alpha particle or a stream of high-energy photons. All these processes are harmful to human cells because of the energy or particles given off during radioactive decay.

Graphic panel representing a drawing of a silhouette of the human torso from the waist up and the lungs shown along with a drawing of the cross section of a lung. Radon gas itself is not generally harmful, but it quickly decays into polonium that settles in the lungs when inhaled. Polonium then decays further giving off more daughter particles and high energy that may damage lung cells.

Graphic panel showing a drawing of a single bar graph representing two causes of lung cancer in the United States. Radon gas exposure in enclosed places is the largest cause of lung cancer (10 percent) after cigarette smoking (90 percent). Radon is measured in picocuries per liter, which describes the amount of radiation emitted during radon decay. The U.S. Environmental Protection Agency recommends that indoor radon levels stay below 4 picocuries per liter.

Graphic panel representing an aerial drawing of the Pinenut Mine and indicating the location of various instruments used to detect and measure radon gas being emitted at the mine. Instruments included radon monitors near the mine vent and ore pile, a time-lapse camera to monitor activity on and changes in the ore pile and to see if movement of ore by heavy equipment affected the amount of radon released, and weather stations to monitor wind speed and direction, temperature, and precipitation.

Graphic panel representing drawings of a large ore pile in the left panel and then later in time, in the right panel, when its size has been reduced because of transporting the ore to a processing facility after mining has stopped. In July 2015, radon concentrations were greater than 3.0 picocuries per liter probably because the mine was still operating. In February 2016, radon concentrations were less than 3.0 picocuries per liter probably because mining operations had stopped, the ore was being removed, and the ore piles were reduced in size.

Graphic panel representing a drawing of an ore pile being rained on and wind blowing over the surface of the pile. Researchers studied the effect of weather on radon concentrations and found that both windy and rainy days at the ore pile resulted in concentrations of radon lower than 3.0 picocuries per liter.

Graphic panel representing a drawing of a mine worker writing on a clipboard. The Pinenut mine has been mostly reclaimed, and the ore piles are gone. The researchers hope that the data collected about radon radiation at the mine will help state and local health officials better quantify risk from radon to people in publicly accessible areas near both active and reclaimed uranium mines.

Photo of a close up view of the rubble from the Pinenut mine ore pile.

References:

Centers for Disease Control and Prevention, 2020, What are the risk factors for lung cancer? web page, accessed 5 January 2021, at https://www.cdc.gov/cancer/lung/basic_info/risk_factors.htm .

Naftz, D.L., Walton-Day, K., Gardner, W.P., Duniway, M.C., and Bills, D., 2020, Natural and anthropogenic processes affecting radon releases during mining and early stage reclamation activities, Pinenut uranium mine, Arizona, USA: Journal of Environmental Radioactivity, v. 220-221, 106266, accessed 5 January 2021, at https://doi.org/10.1016/j.jenvrad.2020.106266 .

Naftz, D.L., Walton-Day, K., Gardner, W.P., Duniway, M.C., and Bills, D.J., 2018, Radon data and time-lapse photos collected outside the Pinenut uranium mine, Arizona 2015-16: U.S. Geological Survey data release, accessed 5 January 2021, at https://doi.org/10.5066/F79Z946T .

National Institutes of Health, National Cancer Institute, 2011, Radon and Cancer, web page, accessed 5 January 2021, at https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/radon/radon-fact-sheet .

Sethi, T.K., El-Ghamry, M.N., and Kloecker, G.H., 2012, Radon and lung cancer: Clinical Advances in Hematology & Oncology, v. 10, no. 3, p. 157-164, accessed 5 January 2021, at https://www.hematologyandoncology.net/archives/march-2012/radon-and-lung-cancer/ .

U.S. Environmental Protection Agency, 2019, RadTown Radioactive Atom: Teacher information web page, accessed 5 January 2021, at https://www.epa.gov/radtown/radtown-radioactive-atom-teacher-information .

U.S. Geological Survey, 2021, Informing future decision making on uranium mining in Arizona: Science for Health and Environment web page, accessed 5 January 2021, at https://webapps.usgs.gov/uraniummine/ .

Authors acknowledge funding from the U.S. Geological Survey Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology), Ecosystems Mission Area. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.