More about prussian blue

Dear Reader,

Now some of my readers have become interested in Prussian blue, this is the miracle drug which removes cesium from human bodies. I was recently reading the work of Peter W. Stephens et. al., Inorganic Chemistry, 2010, 49, pages 1524 to 1534. His paper is about the crystal structures and magnetic properties of mixed oxidation state manganese versions of Prussian blue. This has allowed us to use X-ray technology to look inside a prussian blue crystal.

Here is a chance to look at the potassium version of the prussian blue, it is clear that the potassium atoms are in channels which run through the solid.

K2Mn{Mn(CN)6}

The way in which the prussian blue works is to allow out the potassium, the cesium ions then diffuse in to take the place of the potassium ions. When the potassium ions are replaced in this solid with cesium the larger cesium ions cause the solid to change slightly. Here is a picture of the cesium solid.

Cs2Mn{Mn(CN)6}

I checked the literature and other prussian blue like model compounds have similar structures, one early report was made by R. Rigamonti, Gazzetta Chimica Italiana, 1938, 68, 803-809. Where this italian reported a potassium salt of Co[Fe(CN)6]. I think that due to the ligand field energy effects this was a simple cubic solid which looked just like the cesium one which I showed above.

Now I am going to tell you the story about how I found out about Prussian blue, years ago in 1999 I went on an adventure to eastern europe. I joined Josef Novosad’s research group for a while. While I worked with Josef on phosphorus chemistry (we both share an affinity for this element), between making some interesting compounds which may have improved our understanding of dithioimidodiphosphinates and enjoying the delights of Brno (it is a very wonderful place) we did talk about chemistry.

One of the things which Josef told me about was what he did in his youth, he told me that he was given a job by the communists working on uranium in farmyard animals at a research centre close to Brno. But after the Chernobyl accident he was moved onto cesium in farmyard animals. What used to happen at Josef’s research site was that an animal would be given a dose of 1 MBq of Cs-137, then using additives to the animal’s feed the workers would then try to remove the cesium from the animal.

Before anyone gets worried about the effect of the cesium on the farmyard animal lets do an estimate of the dose which the animal gets. If we assume that the animal is identical to a typical human in size and that it is identical to a human then we can use the data for humans. Using the radiation protection advice from a US university we can get a thing called an ALI for oral exposure to Cs-137. The ALI is the Annual Limit of Intake which for Cs-137 in the US is 100 microcuries. As 1 Ci = 37 GBq this works out as a dose of 3.7 MBq to the animal being the limit. The US limit is worked out based on a 5 rem dose to the body. So the animal will get 1.35 rem. Now some of you might be getting a bit confused with the different radiation units. Here is a look up sheet

100 rem = 1 Sv

100 rad = 1 Gy

1 Curie = 37 GBq = 37000 MBq = 37000000 KBq = 37000000000 Bq

1 milli Curie = 37 MBq

1 microcuries = 37 kBq

So our “animal” will have got a 13.51 mSv dose, this dose is far too small to cause “radiation sickness”. If we repeat the calculation using the ALI value used in Sweden (based on a 20 mSv dose) which is 1.5 MBq then our animal gets a dose of 13.33 mSv. This is not a dose which will make the animals die of radiation sickness and if we use the accepted dose to chance of cancer conversion factor of 5 % for a 1 Sv dose then if we assume that the LNT model is right then if the animal was a human then it would have a 1 in 1500 chance of getting cancer as a result of the cesium intake. As most farmyard animals weigh more than a human the real dose to the animal would be likely to be lower.

To put it in perspective if I got a dose of 13.3 mSv at work then I know that my radiation protection officer would be very very concerned about me but I would not have gone over the yearly limit for a classified radiation worker, but if I got that dose in one month in Sweden then it would trigger an investigation into me. Such a dose is in the range where the national radiation protection authority would want to know what I was doing and how I got the dose. However if a member of the public got that dose at work then I imagine that the national radiation protection would be hopping mad to say the least ! The occupational dose for a non radiation worker is only 1 mSv per year, as a non-radaition worker is unlikely to be wearing a film or TLD badge then it might take quite a lot of extra work to work out the dose compared with the effort needed to estimate a dose for a dosemeter wearing radiation worker.

But lets get back to the prussian blue.

Josef told me that he tried almost every transition metal, I think that he did not try using nickel as nickel is toxic. He then used the batches of the “prussian blues” to try to clean the animals up. What Josef found was that no two batches of prussian blue which he made worked quite the same way in the experiments. So my advice to anyone planning on making prussian blue for medical use in Japan is that the production of the medical grade solid is not a simple matter, I have to confess that I do not know how to reliably make medical grade prussian blue.

If you want to read about Josef’s cesium work then see  H. Prochazka, J. Jandl, J. Novosad, O. Neruda, J. Hejzlar and S. Spelda, Veterinarni Medicina, 1991, 36, 341 to 348. The paper is entitled “Affection of Radiocesium Retention in Miniature Pigs”

The abstract of this paper comments that stable cesium (1 mg per kilo of body weight) is not effective as a means of removing cesium from pigs. Josef and J. Jandl published another paper in which they used a modified zeolite to treat sheep which were contaminated with cesium. This paper can be found at “In-Vivo Reduction of Radiocesium by Modified Clinoptilolite in Sheep”, Veterinarni Medicina, 1995, 40, pages 237-241.

Energy units

OK we need to measure energy sometimes in life, dieters, electric power bills and scientists all need a means of expressing how much energy.

There is the joule (defined by a force and a distance), the foot pound, the electron volt, British Thermal Unit (defined as the energy required to heat a volume of water by 1 degree F),  calorie, the horsepower-hour, kilotons of TNT (for nuclear bomb yields), ergs and some others.

I am not sure what would be the most silly energy unit, but my suggestion if anyone wants a silly unit is the elephant inch. It is the energy required to lift the average elephant one inch and we will define the standard as being done at Camden lock which is close to London Zoo. Please write in using the comments if you think you can devise a more silly unit of energy, please do not worry I will not be replacing the joule and the electron volt in my teaching with the elephant inch.

Units and contamination

Dear Reader,

The IAEA have reported at distances between 35 and 68 km from the stricken plant that the level of contamination by beta / gamma emitters are at levels between 80 and 900 kBq per square meter.

At this point I would like to point out that until we know which isotopes have landed on the land that nobody can make a good assessment of the threat posed to the general public.

But we need to stop for a moment and consider what the symbols T, G, M k, m, n and p mean.

If you have a T before a unit then it means that the unit is 1000,000,000,000 times larger than the ordinary unit which does not have a prefix.

If you have a G before a unit then it means that the unit is 1000,000,000 times larger than the ordinary unit which does not have a prefix. For example the 3 cm microwaves used for both satellite TV and police radar speed guns have a frequency of 10 GHz.

If you have a M before a unit then it means that the unit is 1000,000 times larger than the ordinary unit which does not have a prefix. For example medium wave AM radio broadcasts are at about 1 MHz, for example virgin 1215 was always at 1.215 MHz.

If you have a k before a unit then it means that the unit is 1000 times larger than the ordinary unit which does not have a prefix. For example virgin 1215 in the 1990s was first at 1215 KHz, now the smarter ones of you reading will understand how 1.215 MHz and 1215 KHz are the same value.

If you have a m before a unit then it means that the unit is 1000 times smaller than the ordinary unit which does not have a prefix. For example the millimeter is 1000 times smaller than a meter. The width of a finger is about 10 to 15 millimeters

If you have a funny looking u (micro symbol) before a unit then it means that the unit is 1000,000 times smaller than the ordinary unit which does not have a prefix.

If you have a n (nano) before a unit then it means that the unit is 1000,000,000 times smaller than the ordinary unit which does not have a prefix. A medium sized molecule such as benzene is typically in the nanometer size range.

If you have a p (pico) before a unit then it means that the unit is 1000,000,000,000 times smaller than the ordinary unit which does not have a prefix.

I am sure that you can make up or find some more examples to use the different prefixes.

A final word of warning about the Bq and the curie. For many purposes the Bq is very small it is like trying to express the weight of a man in terms of grains of rice while expressing many everyday levels of radioactivity in curies is like expressing the weight of a cat in tons.

One curie is the same amount of radioactivity as is in one gram of radium-226 (Nightmare isotope), which is the old fashioned unit for radioactivity levels. While people in Europe tend to use Bq the americans still use curies. 

The Bq (becquerel) is one radioactive decay event per second which is a lot smaller.

One curie (Ci) is 37 GBq, now I imagine you can see why I think that the curie is too big for many uses while the Bq is a bit on the small side for many purposes. The way to deal with this problem is to use the prefixes.