Mud in Fukushima

Dear Reader,

It has come to my attention that mud at the bottom of swimming pools at Fukushima has been found to contain cesium. A film has appeared on another blog which claims to be a reading of the work of a Masakazu Honda. In this film and the text it points out that the mud at the bottom contains lots of cesium while the film suggests that nothing was noted when the water was tested.

This is perfectly reasonable in terms of chemistry, I have been saying since the accident occurred that the cesium will stick to soil minerals. I would say that it is important to consider both the water in the pools and the mud at the bottom. I think that the best thing might be to use a swimming pool vacuum cleaner to suck out the mud. The mud will then have to be sent away as radioactive waste. It may be best to condition the mud with cement (plus put it into plastic drums) before sending it away as these actions will make a release of radioactive muck less likely during transport.

The cement will not bind the cesium, but it will hold the radioactive soil particles in a solid which will not form mobile dust. The best thing may be to put the waste into a waste store. If this is left for 300 years then the cesium will decay away and the drums will be giant paperweights.

Be careful of two groups of people, one lot to watch out for are the professional doomsayers. They seem to be unable or unwilling to find a real and useful job and then they make their money by scaring the wits out of people. They will tell you that the Fukushima accident has extinguished all hope and that there is nothing which we can do to protect ourselves or clean up our environment. The second lot are those who claim that there is absolutely nothing to worry about and that you should ignore the results of the Fukushima accident. My advice is do not trust either of these “friends”, they are false friends who will lead you into different but equally bad places.

Cesium chemistry in Japanese soils

Dear Reader,

After having spent much of sunday in a fruitless search for a storage box for my garden tools, I get the chance to write to my beloved readers another blog entry. Now all along I had been making the prediction that the cesium would stick like glue to the soil and stay in the top layer. Some workers have examined soil samples and in a paper (Takeshi Fujiwara, Takumi Saito, Yusa Muroya, Hiroyuki Sawahata, Yuji Yamashita, Shinya Nagasaki, Koji Okamoto, Hiroyuki Takahashi, Mitsuru Uesaka, Yosuke Katsumura and Satoru Tanaka, Journal of Environmental Radioactivity, 2012, 113, 37-44) an examination of soil samples from the Fukushima area has been reported. In this paper it has been shown that the cesium is concentrated in the top layer of the soil.

Circa 70 % of the cesium is in the top 2 cm in the soil, while the iodine was more mobile. The good news is that the cesium will not enter ground water, further good news is that plants with deep root systems are unlikely to absorb much cesium. The bad news is that the cesium will be in the right part of the soil to enter grass via its shallow roots and the fact that the cesium is in the upper layers of the soil will increase the external threat due to gamma photons.

It is interesting to note that the Japanese may not worked out a sensible way to store the contaminated soil which is removed during the clean up of land. It has been reported that people are being required to store contaminated soil from cleaning up their own gardens on their own land. I think it would be better if industrial estates were used as places to store the contaminated soil while the government find a place to store the soil for the next 300 years.

I have spoken to my legal advisor about human rights, and my advisor told me that the right to have a safe environment could override the right to object to a waste store in a given town. I hold the view that if the waste stores are sited well away from homes and other places where the general public spend a lot of time, then it is OK to raise the dose rate in the waste store. The waste store should be designed to avoid releasing cesium into the environment and the construction of the waste store should be done in such a way that it does not increase the dose rate at the edge of the site. I think that the reference dose rate for the latter point should be the dose rate at the edge of the site before the clean up is done.

If the dose rate at the edge of the site is 2 microSv per hour, then this will give a person a dose per year of 17.5 mSv which is a big dose for the general public. But if the dose rate at the same spot was 2 microSv per hour before the clean up which generated the waste which will go into the store is conducted then the clean up will have a neutral effect at the edge of the waste store but will have a good effect on the majority of the land.

I may do some calculations on the subject if I get time in the near future.

Palomares and the H-bombs

Dear Reader,

Now some doomsayers may have tried to tell you that once radioactivity appears in soil that you should give up all hope, also on the otherhand some false prophets of insincere reassurance will just tell you to stop worrying and that “everything will be OK”. My advice is not to trust either of these two false friends.

The story of the air crash which involved four H-bombs has popped up again, the BBC report that the local people in Spain are fifty years after the air crash unhappy about what has been done.

The BBC report suggests that the local farmers have a problem getting a good price for their produce at market. I would like to point something out.

The plutonium in the H-bombs would have been in the form of the metal, during the accident this would have been burnt into plutonium dioxide. Now the thing to note about plutonium dioxide is that it is very hard to dissolve in acid, also it is not mobile in soil. Any plutonium which was in a water soluble form is likely to have bonded to the soil minerals thus making it impossible for plants to absorb it via their roots.

M.I. Sheppard and D.H. Thibault, Health Physics, 1990, 59, 471 to 482 gives the binding constants for most metals to the four common soil types. It lists for plutonium the following Kd values.

Sand, 150 L/kg

Loam, 1200 L/kg

Clay, 5100 L/kg

Organic, 1900 L/kg

This means in a bucket containing a mixture of clay type soil and water that the plutonium content of the soil (Bq per kilo) will be 5100 times higher than the plutonium content of the water (Bq per litre).

Hence when 1000 Bq of plutonium is added to a litre of water mixed with a kilo of clay type soil, then the soil will absorb 999.8 Bq of plutonium while 0.2 Bq of plutonium will stay in the water. This calculation is for a static batchwise experiment but it will help experts in the field make predictions about the mobility of plutonium solutions in soil.

Another good bit of news is the fact any plutonium dioxide in the dust will not be well absorbed if it is swallowed (dust on the surface of the food), so orally the plutonium dioxide is not a great threat to life and limb. If you were to swallow a well sintered particle of plutonium dioxide it will pass unchanged through your digestive system.

However plutonium dioxide in the lungs is very dangerous to a persons health, I think that a key thing to do in Spain is to keep the plutonium in the most contaminated soils from entering the air as a dust. I think that the ban on building, farming or walking in the contaminated area is a good idea. But I think that it might be a good idea to pour concrete or asphalt onto the worst hot spots to try to fix the soil to keep it from becoming mobile again.

One of the problems with plutonium is that the colloidal particles of clay can make the plutonium mobile, while the plutonium does not move freely through the soil in aqueous solution the colloidal particles can move through the cracks in the soil. Thus sealing the soil would help to stop the plutonium from reaching the surface again in the form of dust.

Gamma spectrum of Fukushima soil

Dear Reader,

In case you want to look at a gamma spectrum for the soil from about 20 km from the Fukushima site then I suggest you look at the paper published by Keiko Tagami, Shigeo Uchida, Yukio Uchihori, Nobuyoshi Ishii, Hisashi Kitamura and Yoshiyuki Shirakawa, Science of the Total Environment, 2011, volume 409, pages 4885 to 4888.

The paper concludes that the only isotopes released from the plant were noble gases and volatile elements such as I, Te and Cs. The isotopes detected in large amounts were I-131, Te-129m, Cs-134, Cs-136 and Cs-137. Very small traces of Nb-95, Ag-110m and La-140 were detected but these levels were too low for measurement.

No Zr-95, Ru-103 or Ru-106 was detected which suggests that it is very unlikely that a large scale release of plutonium has occurred. If anyone suggests to you that plutonium has been released in large amounts then bear in mind that Zr-95 is a good mimic for plutonium in nuclear fuel. It forms a dioxide and a Perovskite SrZrO3 both of which are very similar to the plutonium dioxide in their boiling points and water solubilities. If a large scale plutonium release was to occur from a nuclear power plant accident then I would expect zirconium-95 to be found in the same places as the plutonium. The zirconium-95 is much more easy to find as it is a strong gamma emitter while plutonium is only a weak gamma emitter.

Molecular boxes

OK a bit more about prussian blue and what are known as coordination polymers. The idea of a coordination polymer is that it is a repeating network where bridging ligands link each metal centre to the next, thus making a polymer.

To understand them we need to build up to it, it is not a good idea to try to run before you walk. Lets start with a metal complex which has lone pairs poking out into space ready to bind to something else. Err Oh Err how about [CpFe(PR₃)(CN)₂]^- this is a 18 VE complex. For those of you who do not know what the 18 VE rule is then I suggest that you read Tony Hill‘s book which will explain the 18 VE rule. A copy of organotransition metal chemistry by Anthony Hill can be obtained from the RSC.

Here is a picture of the anion, you can see it has the two nitrile groups which each have a lone pair on the nitrogen atom.

The cyclopentadienyl iron triphenylphosphine dicyanide anion

Now here is a complex where the Cu(PCy₃) group is used, this group is a weak lewis acid so it has the ability to bind to lewis bases such as the lone pairs of the cyanide groups of the iron fragment.

You can now see the square-ish arrangement of two copper atoms (green) and two irons (yellow), what you are looking at may be a bit of an “atomic fog” but do not worry yourselves too much.

The diiron dicopper square complex

As I feel kind here is a picture of the inner core of the complex, I have removed the carbon groups attached to the phosphorus atoms.

Copper iron square complex without some of the groups to give you a better look

Now if we use three cyanides to link a metal to three other metals we can make a cube, well it is a bit of a distorted cube. I am sure that the more able minded persons reading this can understand how this is step towards a infinite solid with lots of cubes in it. Here is a picture of it. Before you ask the cage is anionic, and the atom at the centre of the cage is a potassium. This complex was published by T.B.Rauchfuss in the Journal of the American Chemical Society, 2007, 129, 1931.

The cube of eight cobalt atoms bridged by 12 cyanide ligands

The cube is capped with cyclopentadienyl and tetramethylcyclobutadiene ligands. For those of you who can not see through the atomic soup (or atomic fog) here is the cube without the capping ligands.

The cobalt cage without the capping groups

* If as a university teacher you do not get on with Tony Hill’s book then you can always replace this with another book.

Prussain blue

Dear Reader,

I have explained how cyanide can bind to metals such as iron to form complexes, these complexes have lone pairs poking out which can bind to other metals. Here is a picture of a unit cell of prussian blue.

A unit cell of a cesium nickel iron cyanide

The carbons are black, the nitrogens are blue, the irons are purple, the nickels are gold coloured and the green atoms are the cesium.

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.

Have the sunflowers failed

Dear Reader,

I have read that the sunflower plants in Japan have failed to remove much cesium from the soil, it was reported in a Japanese news paper that suggested that if 10 kilos of sunflowers are grown per square meter that only 0.2 % of the cesium will be removed. The problem with phytoremediation is that ability of the sunflower plants to remove the cesium will depend a lot on the Kd value for the soil. I know that sunflowers which are grown under soil free (hydroponic) conditions are very good at absorbing the cesium.

This failure of the sunflowers to absorb the cesium may in some ways be a good thing, it may suggest that the Kd value for cesium on the Japanese soil is very high. In some ways a high Kd value for cesium is good, if the cesium sticks like glue to the soil then it will be less able to enter plants. The best possible soil for the Japanese to have would be a potassium rich soil which has plenty of clay in it.

I predict that for farming that this year will be the worst for cesium, this year cesium will have been able to absorb through leaves and the other surfaces of plants which are above the ground. In future years the cesium will have to pass through the soil, the soil will act as a filter which will reduce the uptake of the cesium by the plants.

The Japanese have found that by removing the top layer of the soil that they are able to greatly lower the cesium contamination level, but they will create vast amounts of contaminated soil. I would suggest that for the worst hot spots that the Japanese should scrap the soil but for less contaminated areas they should deep plough the soil to put the cesium out of reach of the roots of grass. An alternative is to only grow oil crops like sunflowers / rape or plants which have very deep root systems.

It has been shown that sunflowers can be grown on radioactive land with very little of the cesium entering the plants, which sets us up well for biodiesel production.

Very little cesium is transferred into the part of the plant which is pressed to provide the oil. So the sunflowers could play a role in the cleanup of the area. The farms near to the stricken reactors could be used to grow vast fields of oilseed rape. This oilseed rape could then be pressed to give oil which will be very low in cesium. The oil could then be converted into FAME diesel, the conversion process is likely to lower the cesium content yet further.

The FAME biodiesel could help Japan as it normally has to import lots of motor fuel, so the product of these farms would have a use rather than being a crop which has no use. So maybe together with things like prussian blue the sunflowers may have a role to play in the recovery.

Iodine

Dear Reader,

I have reader that iodine was been detected in the soil south of the stricken nuclear plant in Japan. The problem is that due to radioactive decay of the iodine-131 it has not been possible for a long time to detect the iodine-131. For those who do not know it, this isotope of iodine is the isotope from a nuclear accident which tends to cause the most harm to the health of the general public.

But it is possible to make an estimate of how much iodine-131 contamination occurred to enable retrospective dosimetry to be done, the way to do it is to measure the very long lived iodine-129. In the areas of the former USSR which were strongly contaminated by the Chernobyl accident some soils samples have been examined. R. Michel et. al. in Science of the Total Environment, 2005, 340, 35-55 reported how the man made long lived iodine-129 has been used to make an estimate of the shorter lived iodine-131.