Masashi sent another update today - this time providing some information about the conditions affecting the spread of radioactivity in the region.
He wrote that extremely high level of radioactive materials were found in Iitate which is about 30-40 km away from the nuclear plant. Today's Japanese TV program explained the mechanism by which Iitate had such a high level of radioactive materials. It is a combined effect of wind and rain. Radioactive materials tend to move sporadically and in an uneven manner. They tend to concentrate in certain areas depending on the weather conditions.
Iitate was affected by the weather condition of March 20th (south-east wind and rain afterward). Attached is the map of the eastern part of Fukushima prefecture showing the regions for evacuation and the region where they are advised to stay indoors. You can see from this map that only the southeast corner of Iitate is within the latter zone.
There are many concerns about the radioactive materials detected in vegetables and tap water that are spread along the food chain, through restaurants and importers of Japanese food. For example, one major Italian restaurant chain restaurant has announced it will stop using vegetables grown at its own farms in Fukushima.
Details of restrictive measures to distribute vegetables can be found at the website of Ministry of Health.