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Fukushima and the smell of iodine

Dear Reader,

Recently one person claimed to have smelled the iodine from the Fukushima accident in the first few weeks, I wanted to consider if this was possible.

Sheng Xu et. al. Environmental Science and Technology, 2014, 49, 1017-1024 states that the atom ratio of I-129 to I-131 is 16:1. We can calculate the I-131 activity per gram of iodine if we make the assumptions that all of the I-127 and I-129 formed as fission products is stable in the reactor.

The fission yeild of I-127 is 1.24657 x 10-3 for U-235 with thermal neutrons, the fission yeild of I-129 is 7.17849 x 10-3 so the I-127 to I-129 ratio will be 0.17 to 1.00. So the iodine chemical concentration from fukushima will be largely dictated by the I-129.

As iodine can be smelled when the concentration is greater than 1 ppm. This is about 10 mg per cubic meter, this is expressed for elemental iodine (natural iodine), which is 7,874 x 10-5 moles per cubic meter. So we should expect 4.92 micromoles of I-131 atoms per cubic meter.

This is 2.96 x 1018 atoms of I-131 per cubic meter.

As

A = Nλ

And λ = ln(2) / t½ = ln(2) / 691200 seconds = 1 x 10-6 s-1

So the activity will be about 3 TBq per cubic meter. Or 3 GBq per litre. If a typical man at rest inhales 0.5 cubic meters per hour (8.33 litres per minute) then he will get a large dose of radioactive iodine. It is worse if you use the assumption made by divers that a typical diver needs about a cubic foot of air per minute.

Lets assume that a human retains 50 % of the iodine which they inhale and then exhale the other half without absorbing it. Then in one minute our 8.33 litre per minute man will absorb a dose of 12.5 GBq of I-131.

The atom ratio was for the iodine on the day of the earthquake, if we assume that the person was exposed to two week old iodine then at the threshold of being able to smell it they would then get a dose of 3.125 GBq of I-131. I think it is safe to assume that very quickly they will get a very large dose in the range of 100s of GBq (within an hour).

I have never worked out how many GBq of I-131 would be required to kill a typical human (I will not publish an estimate for public safety reasons) but the I-131 dose is greater than the amount I would expect to kill off the thyroid. From what I know about chemistry and biology I think it is safe to say that this intake of radioactive iodine will require specialist treatment for the person to stay alive for weeks, months and years. This is because this dose will at the least cause thyroid gland failure.

As large numbers of people with total thyroid failure have not appeared I think it is safe to say that this extreme iodine exposure of the public did not occur either in Japan or the USA. I would ignore the population who have been diagnosed or treated for thyroid failure by alternative medicine for several reasons. My main reason is that I do not think that alternative medicine would be able to cope with keeping a person with no thyroid alive.

I thus hold the view that anyone who claimed to have smelled the iodine from Fukushima is mistaken.

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