Below is a diagram showing that Radon-222 is element 86 (has 86 protons), has 136 neutrons, and 86 electrons, with a full 8 in the outer shell, making it pretty much inert chemically.
Radon, although it is chemicall inert, and therefore doesn't bio-accumulate through a chemical process, is still extremely dangerous from a radioactive standpoint. Radon is a type of "NORM", a.k.a. "Naturally Occurring Radioactive Material", and anyone can easily be receiving dangerous levels of radiation exposure without even realizing it.
Below is a diagram of the decay chain for U-238, and the portion that interests us begins in the middle, at Radon-222 (Rn). There are several very damaging radioactive decays that will occur before a stable (non-radioactive) state is reached. Thus one inhaled Radon atom can inflict biological damage over a series of radioactive decays. All of these decays are internal, and therefore the alpha and beta particles are absorbed into living tissue inside the lung.
Uranium-238 at the top of our decay chain, tends to be more concentrated in granite than in other soils and rocks. Below is a map showing the estimated prevalance of Radon-222 within the US.
Radon is particularly nasty because due to its density, it tends to accumulate in basements, where there is often little air circulation. If an atom of Radon decays while in the lungs, it becomes a radioactive atom of lead, which is no longer a gas, and will therefore not be exhaled. The radioactive particle will very likely stay in the lung. Afterwards, the radioactive lead atom(s) will continue to decay in a series of events, damaging the DNA in the lungs.
Below are the some statistics on a variety of causes of deaths annually. Clearly Radon is a hazard that should be taken very seriously.
Prior to moving into our new house, we requested a Radon test, and the result was 215 pCi/L (picoCuries per Liter). The limit is 4 pCi/L. The concentration of Radon in our basement was about 53 times the limit.
The biological damage inflicted by the radiation of 4.0 pCi/L of Radon (continuous exposure, annualized) is equal to the biological damage from 100 chest x-rays.
In equivalent biological damage for cigarettes, 4 pCi/L is equal to 10 cigarettes a day. So the Radon in our basement had the biological damage equivalent to 530 cigarettes a day or 5300 chest X-Rays per year. Not good.
The corrective measures for Radon however are pretty simple and inexpensive. The basement (particularly penetrations for utilities) is sealed up, the dirt in the crawlspace is covered with a plastic liner.
A continuously-operating fan is installed that takes suction from underneath the liner and from underneath the floor in the basement. This ensures any Radon will be swept away and vented before leaking into the house.
After remediation, a follow-up test showed that our Radon levels had been reduced to 0.5 pCi/L, or about 1-1/4 cigarette per day, if you never leave the basement. If I can live in Bakesfield air for 8 years, I can certainly deal with that! :)
I highly recommend that anyone who has a basement have their home tested for Radon. It's cheap. The test is definitely less expensive, painful, and deadly than getting lung cancer.