Sheldwin Yazzie

Project title: Assessing Indoor Radon Exposure on the Navajo Nation

Degree: PhD | Program: Environmental and Occupational Hygiene (EOHY) | Project type: Thesis/Dissertation
Completed in: 2017 | Faculty advisor: Michael G. Yost


This study was done to provide an assessment of indoor radon exposure on the Navajo Nation, a geographic region in the Southwest U.S. with naturally elevated levels of uranium in the soil and rocks. Radon is a decay product of uranium and is a known lung carcinogen. Radon has no odor, color, and can pass from the soil into homes. The Navajo Nation also has a legacy of uranium mining with over 500 abandoned uranium mines exposing nearby communities to uranium waste tailings, which were sometimes used to build homes. As a result, communities living in a geographic region with elevated levels of uranium impacted by uranium mining could potentially be exposed to higher levels of radon. To measure indoor radon levels on the Navajo Nation, we recruited a sample of volunteers from the Community Uranium Exposure Journey To Healing (CUEJTH) Program. The CUEJTH program provides education on the health effects associated with uranium to communities across the Navajo Nation. To increase the number of homes with indoor radon measurements, we combined the CUEJTH indoor radon measurements with indoor radon measurements collected through the Navajo Birth Cohort Study (NBCS), which is an on-going epidemiologic study on the Navajo Nation. Using the two datasets of indoor radon measurements, we developed an indoor radon prediction model for homes on the Navajo Nation. To develop our indoor radon prediction model, we used a combination of data collected through both the CUEJTH program and NBCS in combination with existing geographic land predictors identified in the literature as known predictors of indoor radon levels. We used a land use regression model in combination with spatial mapping to develop our model. Key findings in our study show that indoor radon levels depend on both the house type and the sediment soil uranium concentration. We also observed a spatial pattern informing us that in addition to the type of home and sediment soil uranium concentration, that where the home is located matters as well. By location, we are referring to where the home is located which is a combination of geospatial factors. In addition to the soil uranium concentration at each home location, where the home is built along with the microclimate around the home, i.e., the temperature during radon testing and the elevation of the home are associated with indoor radon concentration levels. The findings from this study could be used the Navajo Nation to encourage indoor radon testing for homeowners on the Navajo Nation, but also to raise radon awareness in areas predicted to potentially have elevated levels of indoor radon. URI