Radioactive tests on rice have been completed in more than half of the Tohoku and Kanto regions, and radioactive cesium has been detected in 4 percent of the samples. But the highest level detected so far is about a quarter of the government's safety limit. Based on the interim results, shipments of rice have started in municipalities in 15 prefectures.
A preliminary examination is conducted while the rice is still growing and another test is carried out after the harvest. Rice can only be shipped if the amounts of cesium in the post-harvest test are below the government-set safety limit of 500 becquerels per kilogram in all the locations within a municipality. Preliminary tests have been completed in 7 prefectures, but not in Fukushima or Miyagi.
Radioactive cesium has been detected in 72 places so far, including 64 locations in Fukushima Prefecture, where the Fukushima Daiichi power plant is located. But the highest level detected was 136 becquerels per kilogram, which is about a quarter of the government's safety limit.
The main test is being conducted in 17 prefectures, and has been completed in more than half of them. Radioactive materials were detected in rice harvested in 22 locations. But the highest level detected so far is 101.6 becquerels per kilogram, or one fifth of the government's safety limit.
http://www3.nhk.or.jp/daily/english/18_20.html