Brasnjevic et al.  summarized the evidence showing that single-strand breaks accumulate with age in the brain (though accumulation differed in different regions of the brain) and that single-strand breaks are the most frequent steady-state DNA damages in the brain. As discussed above, these accumulated single-strand breaks would be expected to block transcription of genes. Consistent with this, as reviewed by Hetman et al.,  182 genes were identified and shown to have reduced transcription in the brains of individuals older than 72 years, compared to transcription in the brains of those less than 43 years old. When 40 particular proteins were evaluated in a muscle of rats, the majority of the proteins showed significant decreases during aging from 18 months (mature rat) to 30 months (aged rat) of age. 
Of course, radon is in the natural outdoor air as well, but it is diluted by all the air that is available. The Environmental Protection Agency (EPA) did a national survey in the United States and determine that the average indoor air concentration ( picocuries of radon per liter of air) is about three times higher than the average outdoor air concentration ( picocuries per liter). The average indoor air concentration is three times less than the recommended limit ( picocuries per liter). Even though, on average, we could expect our house to have about picocuries per liter of radon, the EPA estimates that nearly 1 out of every 15 homes in the United States has elevated radon levels.
In the USA, 858 million tonnes of coal was used in 2013 for electricity production. With an average content of ppm uranium and ppm thorium, US coal-fired electricity generation in that year gave rise to 1100 tonnes of uranium and 2700 tonnes of thorium in coal ash. In Victoria, Australia, some 65 million tonnes of brown coal is burned annually for electricity production. This contains about ppm uranium and - ppm thorium, hence about 100 tonnes of uranium and 200 tonnes of thorium is buried in landfill each year in the Latrobe Valley.