16 April 2011

Iodine 131 and a classic magicians' distraction technique.

This was posted to www.llrc.org today

Iodine 131 and a classic magicians' distraction technique. 

This post is about radio-Iodine but we have doubts about going with it. If the authorities can get us all thinking about Iodine and then reassure us that actually it's not a problem except for people in Japan (which is broadly true) then we might not realise that the really dangerous isotopes - Plutonium, Uranium, Strontium, Tritium in particular - are not even being reported. This is a massive failure of Governments' duty of care. 

However, with that caveat, we'll fall into the Iodine trap because we have received many requests for advice since the Fukushima emergency began. 

Our early advice on taking stable Iodine is unchanged. It is here

The European Committee on Radiation Risk has published amethod for calculating doses from drinking water or milk contaminated with Iodine 131. ECRR's main message is reassuring about the risks, so far as USA and Europe are concerned. They are not much different from what you hear from official sources.Calculating doses from Iodine.

Take the figure for Becquerels per litre (Bq/l). (There is information on the internet. LLRC has no resources for monitoring it all). If, as in USA, the radioactivity levels are expressed in picoCuries (pCi), convert pCi to Becquerels (Bq) by multiplying by 0.037.

To convert a dietary intake into a dose multiply the Becquerels by 0.11 and the answer will be the dose in microSieverts. For example, if a litre of water is contaminated with 0.5 Bq, drinking it will give 0.5 x 0.11 = 0.055microSv. (This uses the ECRR adult dose coefficient for Iodine 131 which is slightly different to the ICRP dose coefficient - see ECRR 2010 p. 244).

The cancer risk associated with this dose is small. It can be calculated by dividing the dose in microSv by 1 billion. For the above example this means that if a billion people each drank a litre of water contaminated with 0.5 Bq then 5.5 of them would develop cancer over a period of 50 years. The individual person would increase his or her chances of getting cancer by 1 in 182 million. (This uses the ECRR cancer risk coefficient of 0.1 per Sievert which is different to the ICRP risk coefficient 0.05 per Sievert - seeECRR 2010 p. 180).

Note that this calculation is for a single intake. Iodine 131 loses half of its radioactivity in 8.04 days. This means that if your water supply comes from rainfall and if the rain becomes contaminated in a single episode the radioactivity will decay to 1/16th of its original concentration during a month and so on. That's assuming no further releases from the reactor affect your region.

Black Ops on CRIIRAD?
In the last few days many websites and newspapers have misreported Iodine dose figures from the French NGO CRIIRAD. It is claimed that CRIIRAD has said if a child under 2 years ingested 50 Becquerels of Iodine 131 the dose would be
10milliSieverts. At best, this is a transcription error; at worst it's a propaganda attack intended to discredit good sources of independent advice by making them look like scaremongers. 

CRIIRAD actually said:

Les enfants en bas âge (0 – 2 ans) sont les plus vulnérables : l’ingestion d’une cinquantaine de becquerels d’iode 131 suffit à délivrer à leur organisme une dose de
10 µSv. (Children under the age of 2 are the most vulnerable. Ingesting about 50 becquerels of Iodine 131 is enough to give them a dose of 10 µSv.) 

That's 10 microsieverts, a thousand times smaller than 10 millisieverts. 
We have checked the calculation. It appears that CRIIRAD has used ICRP dose and risk coefficients and a ten-fold multiplier to correct for the small body mass of these little children. This is reasonable (for any given intake, a small body mass means a larger dose). According to LLRC's arithmetic the effective dose to the child is 11µSv. Using ECRR dose coefficients it would be 27.5µSv. 

So beware of nonsense on the net. The micro / milli confusion can arise because the International System of Units (SI) uses the letter m to stand for milli or 1/1,000. The Greek letter mu (µ) stands for micro or 1/1,000,000. Some software packages use the Symbolfont to allow Greek characters and the key you press to get µ is the "M" key. If someone pastes the resulting text into an editor that doesn't recognise Symbol it will give an m. It looks like a small error but in this case it's a thousand times wrong.

If you have more questions email us. We get a lot of emails. We can't answer them all, but we read them all and they influence what we write about here.

Bad news and good advice for Fukushima's refugees
Iodine131 affects the thyroid gland. A few years ago the New York Times reported that doctors had found a puzzling increase in thyroid cancer in New York State. Here's the link. The increased cancer rate was driven by immigrants from Belarus and Ukraine, many of whom settled in New York. Their doctors and, presumably, public health officials didn't realise that it was important to watch for changes to their thyroids, while back in the homeland the people who stayed behind were monitored closely and treated early. Eventually, the emigrés' thyroid cancers became impossible to ignore. Unfortunately, in many cases they were diagnosed too late. 

Apologists for nuclear power claim that the increase in thyroid cancer in the Chernobyl-affected territories is an artefact caused by increased vigilance - more thyroid cancers were detected because doctors were looking for them. (This quote is from the BBC's disgraceful Nuclear Nightmares mockumentary of 2006.) They think this gets radioactive fallout off the hook. The New York experience shows the opposite; radioactive fallout caused the cancers and lack of vigilance killed the victims. This is a powerful warning to people who have left the blighted parts of Japan. Don't think you have left the radiation problem behind; it might have come with you. If you think you have been exposed, make sure your doctor knows it. Get regular checkups long-term. If medical people on LLRC's circulations send us relevant advice we will post it later.

1 comment:

Anonymous said...

Hello -

Can you please explain how to convert micro Becquerels to picocuries?

I'm trying to compare Scotland's monitoring results with the U.S., and Scotland measures in micro Becquerels.

Thank you.