It has come to my attention that cesium-137 and some other radioisotopes of cesium have escaped from the stricken plant in Japan. These radioisotopes have been deposited onto land, where they might now be able to pose a threat to humans.
While this event is not good it is not hopeless, I am imagining that farmland and urban areas in Japan may be subject to contamination with cesium. The cesium is likely to be deposited onto the surface of soil, where it poses two threats.
Firstly it is an external threat, the 700 keV photons from Ba-137m (which is formed by the beta decay of Cs-137) can whizz around and then hit people.
Secondly the radioactive cesium can be transferred from soil into plants, these plants can now be eaten by humans and/or animals. I am ignoring for a moment the threat to drinking water, as well water has been filtered through soil. As long as the soil has some clay it will remove the vast majority of the cesium. Most of the cesium will stay in the top layer as it has a high affinity for clay.
The first (external) and second (internal) threats can be mitigated in a simple method. I will not say that this method is a perfect cure as it may require hours of hard work. Also it may damage gardens, woodland and farmland.
I would say that for many cases that by mixing up the layers of the soil by digging it that the threat from the cesium can be lowered, by mixing up the soil by ploughing, using a spade or a rotorvator much of the cesium can be buried out of reach of the roots of grass and mushrooms. As a result the radioactivity level in these plants will be lower than if the plants were allowed to grow on undisturbed soil.
Also the gamma photons from the buried radioactive cesium will have to pass through soil, while the radioisotopes in the soil directly below your feet might not have to pass through much soil. However the photons from soil which is some distance from you will have to pass through a much thicker layer of soil. As a result many of the gamma rays will be absorbed in the soil before they reach the person.
If the contamination is dire then you may need to go to the next level, by scraping the top layer of the soil off the land the cesium can be removed, if a hole is dug then the cesium contaminated soil can then be dumped into the hole. The removed top soil will then need to be replaced.
The digging may disrupt the land, and in some cases it will not be possible. For example on a steep hill side it may be impossible to plough the land. Also in some areas of land the idea of digging it up would be an outrage. Imagine the outrage at the idea of digging up the local grave yard, but for many areas of land the use of digging can be used to create lower radiation areas. I imagine that land near houses and schools could in some areas be subject to deep digging to bury the cesium out of harm’s way.
Also some plants are potassium hyper accumulators, all plants have a tendency to accumulate potassium but some have evolved over the years into super accumulators of potassium. This allows these plants to grow on low potassium soils, sadly these plants also tend to be very good at absorbing cesium. One cure is to use a high potassium fertilizer to reduce the absorption of the cesium, sadly this treatment will alter the soil chemistry greatly, this in turn will allow new plants to grow on the land. This change may cause chaos with the ecology.
Another method is to use prussian blue to lower the transfer of cesium from grass into milk and meat in farmyard animals. Sadly in the case of wild boar it is impossible to get the wild pigs to eat up their prussian blue each day. I hold the view that after a nuclear accident or war that wild game animals will be more cesium rich than farmyard animals which have well controlled diets.
Right now I think that the farming community in Japan and the people in charge of urban areas need to educate themselves on how to take countermeasures against radioactive contamination. For example people need to be careful about a meal of elk and mushroom soup !
For urban areas it is important to choose the right clean up method, some expensive methods may not give a good reduction in the human exposure while other cheaper methods might work very well.
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