The Japanese government has said it will likely ban beef shipments from Fukushima, the site of the nuclear disaster that followed the March 11 tsunami. The proposed ban, which is expected to be announced tomorrow, follows the discovery of high levels of radioactive caesium in meat that had already made its way to the food supply, The Guardian reported today. The contamination apparently comes from rice straw fed to the cattle after the tsunami caused a meltdown at the plant that released radiation into the atmosphere. And Fukushima might not be the only beef source where cattle have been affected.

Local media reported that the contamination risk could be more widespread, affecting farms 60 miles from the power plant. Kyodo news agency said it had calculated that as many as 143 cows sent to all but 10 of Japan's 47 prefectures may have been exposed to radiation via feed.

Tests on straw at a farm in Koriyama city in Fukushima prefecture showed caesium levels as high as 500,000 becquerels per kg. Those readings are about 378 times the legal limit set by the government.

Farmers in the area said they had not been told about a government warning, issued days after the nuclear accident, not to give their animals feed that had been stored outside.

Radiation levels of 500,000 becquerels of caesium per kilogram have been found in straw from Fukushima, while meat has been tested with 2,400 becquerels. The government has set a limit of 500 becquerels per kilogram. According to an earlier Guardian article, the radioactive isotope caesium-137 "can cause burns, acute radiation sickness and even death at high doses. It can contaminate food and water and, if ingested, gets distributed around the body, where it builds up in soft tissues, such as muscles."