I suspect that the next post is going to make people hopping mad with me, it is about the idea of using radon-222 as a medical treatment. Now before we go any further I would like to point out that I have no vested interest in the radon industry. Nor do I have a personal grudge against the radon therapy industry.
Now we will begin, I come from a school of thought that holds the view that radon-222 is horrible, this school of thought is the vast collection of people in the radioactivity business who live to hate radium-226 and its daughters. Rather than being a nice playful radioisotope radium-226 is considered to be a nasty so and so. It is an alpha emitter which forms a volatile daughter which also emits an alpha and then attaches its self to dust and smoke particles. In this way it creates a horror of sticky alpha active bits which stick in the lungs and do you a lot of harm.
By comparison plutonium-239 is a much nicer radioisotope to work with, it will not diffuse through gloves or fly through the air with great ease.
Some time ago a student (Hanna) at Chalmers was starting a PhD in radium chemistry, and she had a problem. She needed to work in a glove box. The state regulator were not willing to license the work unless it could be shown that the radon was trapped rather than being dumped up the stack. As an inorganic chemist I got involved, I applied what I know about zeolites and xenon to the problem and I then told the young lady of the joys of silver exchanged zeolite. This then resulted in a paper on radon and silver (Hanna Hedström, Mark Foreman, Christian Ekberg and Henrik Ramebäck, Radiochimica Acta, 2012, 100(6), 395). We will keep the radon and silver story for another day, back to radon.
I checked the yearly intake limit for radon-222 and for inhalation it is 10 mCi when it is pure, but it is normally encountered with the daughters present. The limit when the daughters are present is 100 μCi (0.1 mCi). For comparison polonium-210 (half life 140 days) has a limit which is lower at 600 nCi per year, I would reason that the longer effective half life of the polonium in a human is likely to be responsible (at least in part) for this difference.
So I went and looked for a short lived noble gas, so I looked at the limit for xenon-133 (5.2 day half life), while there is no ALI for this isotope there is a DAC of 100 nCi (0.1 μCi) per litre. The DAC is a derived air concentration which is the limit for the air which you can breathe for 40 hours a week for one year.
I checked the DAC for radon-222 and it was much lower at 0.00003 μCi per litre (when the daughters are present), which works out as 0.03 nCi per litre or 3 pCi per litre. Now it should be clear to you that the USA’s goverment (NRC) hold the view that radon is very much worse for your health than xenon-133 is.
Even if we use their DAC for radon when the daughters are absent (400 pCi per litre) it is a lot worse than the xenon. We need to ask ourselves why.
Lets start by considering the decay energy, the xenon isotope is a mixed beta / gamma emitter which has an average beta energy of 100 keV. If we ignore skin exposure for a moment and only consider the beta dose to the lungs then 100 nCi (3700 Bq) of xenon-133 in air will deliver 370 MeV of energy into your lungs per second.
The alpha decay energy of the radon is 5489.52 keV, 14.8 Bq (400 pCi) of radon-222 will deliver 81.244896 MeV of energy into your lungs (call that 81.2 MeV) which is less energy. But alpha (α) is a high LET radiation which is considered (on the basis of energy delivered) to be 20 times more harmful to your cells than beta (β) or gamma (γ) radiation. So the effect of the radon on the lungs at the limit will be 4.4 times as harmful as the effect of the beta decay of the xenon.
The biggest problem with the radon is that it forms solid radioactive daughters which emit alpha particles, these daughters can lodge in the lungs where they continue to deliver radiation to the lung tissue. The atoms of radon are likely to come out of you when your breath out (some will diffuse into your blood and then go into the fatty tissues). So as a result you can imagine that radon is considered to be a grave threat to the lungs, it is worst when smoke or dust is present.
I recently spoke with a medical doctor from the Czech republic who runs a radon bath treatment site. He told me that in the Czech Republic that inhalation therapy was banned, he told me that one reason was worker safety. He told me that a patient is immersed in a bath of water (circa 5 kBq per litre) in a air conditioned room. The person is kept very still in the bath, I imagine that by avoiding splashing and stirring of the bath that the rate at which the radon is transferred into the air is reduced.
I also imagine that the Czech treatment room is a damp place which should reduce the number of dust particles per litre of air, this dampness will reduce the likelihood of radioactive dust entering a person’s lungs. I think that a bad environment for radon is always a dry and dusty place, the addition of smoke to radon containing air will always make it even worse. I have horrible visions of a uranium miner having a smoke in the mine while driving a poorly maintained diesel truck in the mine. Both the diesel and the tobacco smoke will increase the harm which the radon will do to his lungs.
A better situation would be the same miner now wearing a dust mask driving a well maintained truck in the mine. While I hold the view that it would be best if the miner gave up smoking totally, if he (or she) abstains from smoking in the mine then it would very good for the worker’s health.
So at least in the Czech Republic some steps have been taken to reduce the amount of lung damage.
Now from what I have read so far it is clear that radon therapy does bring with it a risk. I am sure that the supporters of radon treatment and others will point out that no medical treatment is totally without risk. I agree fully on this point, I have never heard of a medical procedure which is perfectly risk free.
But for a medical procedure to be justified, the benefits must out weigh the risks and costs. I will move onto benefit vs cost later.