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For the last couple weeks, Japan has been gripped by a scare over radioactive beef, after it came to light that the existing system for testing beef allowed some contaminated cows to be slaughtered and sold to stores across the country. The situation has caused prices of domestic beef to plummet, and many consumers are turning to imported meat instead.
While contaminated food is a cause for concern, it is no where near as scary as some people are making it out to be. The beef contains radioactive cesium that exceeds Japanese safety standards, but the level of contamination is so low that eating one, two, or even ten contaminated steaks would not be dangerous.
To help put the situation in perspective, here are several different estimates for the amount of radiation exposure one is likely to face from contaminated beef, plus some information about how cesium is expelled from the human body.
Estimates of Radiation Exposure
The Japan Times has a Q&A article that provides some basic facts about the risks of contaminated meat. Its estimate for radiation exposure from eating “highly” contaminated beef is particularly noteworthy:
As of Thursday, the most highly contaminated beef found contained radioactive cesium of 4,350 becquerels per kilogram, according to the Health, Labor and Welfare Ministry. The meat did not reach the market.
Eating 1 kg of the meat is roughly equal to a radiation dose of 82.65 microsieverts (0.08265 millisieverts) for a period during which radioactive cesium remains in one’s body. If a person eats food with radioactive cesium, half the amount remains in the body for nine days for a baby younger than 1. But the duration gets longer as people age, and it takes 90 days for those aged 50.
The 82.65 microsieverts compares with the 100 microsieverts (0.00065 millisieverts) of radiation a person would be exposed to during a one-way flight from Tokyo to New York.
Mainichi’s News Navigator has an estimate for those who have eaten the same contaminated beef every day for a month or a year:
Let’s calculate the amount on the assumption that all the cesium contained in 1 kilogram of beef tainted with 4,350 becquerels per kilogram is cesium 137. If a person eats 100 grams of the meat every day for a month, they will be exposed to about 0.17 millisieverts, and if they eat the same amount of meat for a year, they will be exposed to some 2 millisieverts, according to a calculation method employed by the National Institute of Radiological Sciences. The International Commission on Radiological Protection sets the upper limit on an individual’s exposure to radiation at 1 millisievert a year.
An Asahi Shimbun article has some estimates for beef containing 500 becquerels per kilogram of radioactive cesium. Eating 100 grams of contaminated meat would yield an estimated exposure of 0.65 microsieverts (0.00065 millisieverts). Eating 100 grams of contaminated meat a day for an entire year would yield an estimated exposure of 237 microsieverts (0.237 millisieverts).
A Sankei Shimbun article contains an estimate from Ikuro Anzai of Ritsumeikan University. For beef containing 3,200 becquerels per kilogram of radioactive cesium, eating 200 grams a day for a year would result in a total exposure of 0.01 millisieverts. Although he feels the beef contamination is a serious problem, he nonetheless points out that there is already naturally occurring radiation in the food we eat. Each year, you are likely to be exposed to 0.2 millisieverts of radiation from food containing potassium-40.
A Mainichi Shimbun article has some estimates for beef containing 3,240 becquerels per kilogram of radioactive cesium. It doesn’t contain a single meal estimate, but it does not that one would need to eat 500 grams of contaminated beef a day for an entire year to reach an exposure level that exceeds the official annual exposure limit (1 millisievert?).
[Note: 100 millisieverts a year of radiation exposure is the lowest level at which any long-term increase in cancer risk is clearly evident (1% increase in cancer in a population).]
Expelling Radioactive Cesium From Your Body
From the EPA:
Compared to some other radionuclides, cesium-137 remains in the body for a relatively short time. It is eliminated through the urine.
From the CDC:
Once cesium enters your body, your kidneys begin to remove it from the blood; some cesium is quickly released from your body in the urine. A small portion is also released in the feces. Some of the cesium that your body absorbs can remain in your body for weeks or months, but is slowly eliminated from your body through the urine and feces.
And a quote from the Mainichi, on how eating fruit and vegetables is important:
The structure of cesium 137 is similar that of potassium — which is contained in vegetables and fruits. If you are not following a nutritious diet, you tend to absorb cesium 137 in place of potassium.
The good thing about this scare is that it is pushing the government to expand and improve food testing. Measures are being taken to prevent it from happening again, and the government is facing enormous scrutiny from the media and consumers. The government has already announced that farmers will be paid compensation, and it may even purchase and destroy all beef that exceeds radiation limits.
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