I would like to express my thanks to Dr Susan K Burton (Associate Professor, Faculty of Foreign Languages, Bunkyo Gakuin University) who has provided me with a link to an English translation of an article based on a book by Kunikazu Noguchi (Nihon University) which is about how to reduce the amount of radioactivity you get from your diet. Kunikazu Noguchi’s book is aimed at the general public who quite understandably are worried about radioactive food.
You can read part of it at http://www.japantimes.co.jp/text/fs20110920a2.html
He wrote about vegetables, the release from the Fukushima plant was as a result of overheating fuel. This boiled the more volatile radioisotopes out of the fuel and formed some aerosol particles. These aerosol particles were able then to escape from the plant. Knowing what I know about iodine chemistry during a serious accident I suspect that much of this radioactive pollution was in the form of cesium iodide particles.
He suggests that vegetables should be washed before eating to remove the cesium, I hold the view that produce which was harvested shortly after the accident may have some cesium on the outside. As the cesium from the accident is in the form of a water soluble compound it should be simple to wash it off. I would like to point out that this washing will only remove the cesium which is on the outside of the plant tissue, some of the cesium may have been absorbed into the plant through the leaves. This fraction of the cesium will be impossible to remove by simple washing.
Next years fruit and veg will only be able to absorb radioactivity via the roots. So for next year’s crop the need to wash it to remove radioactive dust will be smaller. I would still advise you to wash your salad vegetables before eating them. This is mostly to remove the creepy crawlies.
The absorption of radioactivity through the roots will be controlled by the soil chemistry, in general the more clay in the soil the smaller the fraction of cesium which will go from the soil into the plants. What will happen is that the clay acts as a ion exchange material, according to L.N. Maskalchuk (Nuclear Engineering International, Soil Contamination in Belarus, 25 Years Later, 2012, page 16.)
I have explained already how the clay traps cesium, the illite clay is able to bind 1+ cations and it has the following strength of binding.
Cs+ > Rb+ > NH4+ > K+
I have already discussed this matter before so we are going to move onto something else. While the Fukushima event has released very little strontium into air, I will explain how we can do something about strontium in the soil. The strontium can exchange for calcium in minerals such as calcite and dolomite, in a similar way to the way in which strontium can mimic calcium in the minerals in bone it can swap with calcium in calcite and dolomite.
The domolite unit cell has the following dimensions
a = 4.795 Å
b = 4.795 Å
c = 15.87 Å
alpha = 90 degrees
beta = 90 degrees
gamma = 120 degrees
The volume of this cell is 315.998
The calcium atoms are at the following locations
0, 0, 1/2
The magnesium atoms are at the following locations
0, 0, 0
2/3, 1/3, 1/3
1/3, 2/3, 2/3
The carbon atoms are in the following locations
0.6666, 0.3333, 0.0733
0.0000, 0.0000, 0.2600
0.3333, 0.6666, 0.4067
0.6666, 0.3333, 0.5933
0.0000, 0.0000, 0.7400
0.3333, 0.6666, 0.9267
The oxygen atoms are in the following locations
0.9167, 0.5833, 0.0733
0.4167, 0.3333, 0.0733
0.6667, 0.0833, 0.0733
0.2500, 0.0000, 0.2600
0.0000, 0.2500, 0.2600
0.7500, 0.7500, 0.2600
0.0833, 0.6667, 0.4067
0.5833, 0.9167, 0.4067
0.3333, 0.4167, 0.4067
0.6667, 0.5833, 0.5933
0.4167, 0.0833, 0.5933
0.9167, 0.3333, 0.5933
0.7500, 0.0000, 0.7400
0.0000, 0.7500, 0.7400
0.2500, 0.2500, 0.7400
0.5833, 0.6667, 0.9267
0.3333, 0.9167, 0.9267
0.0833, 0.4167, 0.9267
The calcite has roughly the same cell. Now some of you good people will have drawn out the unit cell for your selves (well done you good and worthy people !) but for the rest of us who find cells where at least one of the angles is not 90 degrees a real pain. Here is the unit cell. The cell has blue calcium atoms, golden magnesium atoms, orange oxygens and dark gray carbons.
What I think will happen is that some of the calcium sites in the dolomite will be replaced with strontium. I have checked the crystalographic literature and strontium carbonate has a very different unit cell to either dolomite or calcium carbonate (calcite).
Here is the calcite cell for you to look at, please compare with the dolomite cell.
The strontium carbonate (Strontianite) has a very different cell, all the angles for the cell are 90 degrees. Here is the cell for you to look at and enjoy.
Now what I thought would happen is that the occasional calcium atom in calcite at the surface will be replaced with a strontium atom. I had these thoughts when I was out walking the dog, I later looked in the literature and saw that N.E. Pingitore et. al., Geochimica Et Cosmochimica Acta, 1992, 56(4), 1531-1538 which explains how EXAFS shows that the strontium forms a very dilute solid solution in the calcite.
If we start with a pure calcite then a face of it would look like this.
Now if we randomly replace some of the calcium atoms with strontium we get a solid solution of strontium and calcium carbonate which has a calcite structure. Now here it is, I have replaced four calciums with strontium.
What this means is that if we add powdered lime (crushed chalk or limestone) to a soil then whatever strontium is present in the soil will be more likely to be absorbed onto the surface of lime and thus be more unavailable to the plants than it would be before the lime was added. The key thing to understand that this is all about solid solutions, a solid solution is a solid which is part way between two solids with identical strucutres. The best way to think of it is to have an array of tennis balls on a table and to randomly swap some of the tennis balls for cricket balls. Sadly I do not have a pile of tennis balls or cricket balls, but here is a photo of some of my weekly fruit supply.
Now we replace one of the oranges with a lemon, note that the array of
atoms fruits are unchanged in terms of how each one relates to the others. Then we can have a solid solution of oranges and lemons. Here is the photo of the solid solution.
Well I will have more to show you soon, so stay tuned !