Fukushima data show rise and fall in food radioactivity via Nature

Giant database captures fluctuating radioactivity levels in vegetables, fruit, meat and tea.


Little contamination

The safety effort has been commended for being very effective. It also produced a vast database. Stefan Merz, an environmental scientist at the Vienna University of Technology in Austria, and his colleagues have now analysed the database of almost 900,000 samples collected between 2011 and 2014, and publish their results in Environmental Science and Technology1.

The researchers found that during the first year after the accident, 3.3% of food from the Fukushima region had above-limit contamination — these products were then prevented from reaching the market. It rose slightly the following year but by 2014, the proportion had fallen to 0.6%. For Japan more widely, the figures were 0.9% falling to 0.2%, says co-author Georg Steinhauser, an environmental scientist at Colorado State University in Fort Collins. Combined with the fact that people need to eat huge amounts of above-limit food to exceed the annual permitted radiation dose, the chance of anyone exceeding it was very low, he says.

That conclusion fits with several studies, including one done in 20132 that showed that only members of the public who bypassed the monitoring by eating home-grown food — four older residents — showed any elevated radiation levels, and these soon returned to normal when eating food that had been regulated.


Of mushrooms and boar

From Chernobyl and weapons-testing sites in the twentieth century, scientists already knew that mushrooms, which soak up radioactive elements from the soil, have a tendency to accumulate more radionuclides than most other vegetables.

The data from Fukushima show that the radioactivity levels fell quickly in most vegetables: just five months after the disaster, only a handful of samples exceeded the limit. They also showed two peaks for mushrooms, one for fresh mushrooms and the other for dried mushrooms. Tea leaves showed a late spike — they were harvested later than other leafy plants, but retained some radioactivity because older leaves transferred the radioactive elements to younger leaves, says Steinhauser.

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