2012年04月05日 (木)

Commentary: How strict are the new radioactivity food-safety criteria?

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On April 1, the criteria on radioactive cesium allowable in foodstuffs were tightened. For example, its density in rice and other common food must be lower than 100 Becquerel per kilogram. The new criteria took effect one year after the accident at the Fukushima No.1 nuclear power plant. The question is how strict they are. NHK science reporter Yuya Inagaki speaks.  

What is the basis of the new criteria? 

The new criteria on radioactive cesium in foodstuffs are based on the desire to limit exposure to radiation to a maximum 1 millisievert. That is one fifth of 5 millisieverts, the ceiling provisionally set in emergency after the nuclear accident. 

The new criteria divide foodstuffs into four categories:

Vegetables, rice and other common food: allowable radiation dose up to 100Bq/kg.

Milk heavily consumed by children: allowable radiation dose up to 50Bq/kg.

Tap water drunk continually: allowable radiation dose up to 10Bq/kg.

Food for infants considered more vulnerable to radiation than adults: allowable radiation dose up to 50Bq/kg.

The last category was added for the first time to the new criteria.   

Authorities estimate the total sum of exposure per year by different age groups, based on the assumption that half of digested food is contaminated with radiation.

They also take into account the ratios between domestic and imported products available in corresponding categories.

The second most critical group are men aged 19 and over, with a maximum 0.78 millisieverts a year.

The third are women aged 13 to 18, with a maximum 0.68 mllisieverts a year.

The last are infants up to six years old, with a maximum 0.35 millisieverts or so. Note that they eat the least.  

Are the Japanese criteria stiffer than those in other countries? 

Let me compare the Japanese criteria with others. In the United States and the EU, for example, 1,200 Becquerel per kilogram and 1,250 Becquerel per kilogram apply to common food. These numbers are way over the Japanese ceiling of 100 Becquerel per kilogram. Since both regions are currently not involved in a nuclear accident, they can afford to assume a smaller percentage of food is contaminated than Japan can do. Japan assumes 50 percent of food in circulation is contaminated, as opposed to 30 percent in the United States and 10 percent in the EU. 

Let me turn to the Republic of Belarus, known for the Chernobyl nuclear meltdown. The country imposes the following limits:

10 Bequerel per kilogram on drinking water, exactly as in Japan.

40 Bequerel per kilogram on bread, compared to 100 in Japan, where bread is categorized as common food.

80 Bequerel per kilogram on potato, compared to 100 in Japan, where potato is categorized as common food.

100 Bequerel per kilogram on milk and dairy products, compared to 50 in Japan.

Since the Chernobyl accident, Belarus has gradually revised the criteria upwards to the current numbers.   

 

Many people voice their concerns about what will happen to radioactive cesium after being taken into their bodies with food. Scientists say the substance will spread into all muscles, half of it likely to go out in 100 days, 90 percent in 300 days. They say, however, it will take almost two years until 99 percent of cesium goes away.  

投稿者:かぶん |  投稿時間:10:15  | カテゴリ:ニュース解説
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