Radon is a radioactive gas that comes from the natural decay of uranium found in almost all soils. It usually moves from the ground to air and can penetrate homes through cracks in the foundations, trapping radon inside, where it can accumulate. It can also seep in through well water. Waste rock and discarded ore has been used as aggregate for cement and building material in Navajo homes since the 1950s. Due to the amount of tailings that contaminate the area, it can still used unknowingly. Exposure is of high-level concern. Dust becomes Alpha emitters to be inhaled. Building materials can be Gamma emitters, and contaminated soils can also be ingested through wind blowing dust onto food or into the mouth, or that accumulate on produce grown close to, or in, radioactive soil.