One mother had lived in Hiroshima since before the March 11 nuclear accident. The expert at Hiroshima University who measured the density of radioactive cesium suspect it is internal radiation from ingesting contaminated food.
Hiroshima is over 840 kilometers from Fukushima I Nuclear Power Plant.
From Chugoku Shinbun (10/12/2011):
A citizens' group called "Tsunagaro Hiroshima (Let's connect, Hiroshima" announced on October 11 that a minute amount of radioactive materials has been detected from the breast milk of two mothers who live in Hiroshima Prefecture. One of them escaped from Tokyo after the March 11 disaster; the other had lived in Hiroshima since before the disaster. The researcher at Hiroshima University who measured the breast milk says there is no problem feeding their babies with the breast milk.
The survey was done in early October on 4 people who evacuated to Hiroshima from the Kanto region after the March 11 disaster, and on 2 people who had lived in Hiroshima since before the disaster. 100 cc of the breast milk was taken from each mother, and tested by Professor Kiyoshi Shizuma of Hiroshima University Graduate School of Engineering.
A minute amount of radioactive cesium was detected from two mothers in their thirties. The Ministry of Health and Labor uses the provisional safety limit for milk and dairy products for radioactive cesium (200 becquerels/kg) for the breast milk. The citizens' group has not disclosed the detailed numbers as the mothers do not wish the numbers to be disclosed, but says they are well below the standard set by the Ministry of Health and Labor.
Professor Shizuma will continue to monitor the mother who has lived in Hiroshima since before the accident, as "It is possible that radioactive cesium came from ingesting the contaminated food."
The leader of the citizens' group says he will ask the prefectural government to set up a system to test the breast milk and urine, and to measure the radiation in food.