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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.

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2 Responses

  1. Unbelievable Comment by Mr. Yamashita

    • Thank you for your comment; if the subtitles are a truthful translation of Mr Yamashita then I think his comments are not reasonable. But I would like to make you aware of the fact that the European Committee on Radiation Risk is not part of the EU or the European Commission.

      The European Committee on Radiation Risk is an organisation which expresses a series of views which are very far removed from what the majority of scientists working on radiation biology hold. I will confine my response to a view based mainly on UK law.

      In this case the idea that 100 microSv per hour is harmless is not reasonable. While much of the data on the induction of cancer in humans has been obtained investigating events such as radiotherapy, atomic bombings and other events where humans have been exposed to high doses of radiation at high dose rates

      The work on high doses has been extrapolated to low doses, thus making the LNT model.

      If we use the LNT (Linear No Threshold) model then it does suggest as a general rule that the general public should not be allowed to enter an area where the dose rate is 100 microSv per hour. Normally radiation workers will avoid entering any area which such a high dose rate or at least limit the time they are exposed at such a high level.

      In only ten hours a non radiation worker will reach their yearly occupational limit if the dose rate was 100 microSieverts per hour. A classified worker in the UK could work for 200 hours (5 working weeks) in such a place without reaching the 20 mSv limit.

      But UK and Swedish radiation rules require that radiation work should be done in such a way that the dose is kept as low as is reasonable (ALARP = As Low As Reasonably Possible), I think that working up to the 20 mSv limit under non emergency conditions strongly goes against the sprit of the ALARP.

      I know that in the UK and Sweden that at doses of 15 mSv year-1 and about 7 mSv month-1 that the national radiation protection authorities will start to investigate the work that a person is doing. Using the Swedish rules a person could not work for two weeks in a radiation field of 100 microSv per hour without reaching a trigger point for further investigation.

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