Food safety in Japan – experts respond

Expert reaction to measurements of radioactivity in food near Fukushima

The quotes below were gathered by our colleagues at the UK Science Media Centre. Feel free to use them in your coverage.

Prof Steve Jones, independent nuclear and environmental consultant, said:

[In response to figures obtained by the Associated Press on Saturday from the Japanese Ministry of Health]

“Results have been reported for samples of milk taken in Fukushima prefecture on 16, 17 and 18 March, and for leek and spinach taken from Ibaragi prefecture on 18 March.

“Milk samples show concentrations of iodine-131 ranging from 932 to 1,510 becquerels per kilogram, averaging 1,210 becquerels per kilogram; there is one caesium-137 measurement at 18.4 becquerels per kilogram.

“Spinach samples show concentrations of iodine-131 ranging from 8,400 to 15,000 becquerels per kilogram, with an average of 10,450 becquerels per kilogram; caesium-137 concentrations range from 140 to 520 becquerels per kilogram with an average of 350 becquerels per kilogram.

“Leek samples show concentrations of iodine-131 ranging from 200 to 690 becquerels per kilogram, with an average of 450 becquerels per kilogram; caesium-137 concentrations range from 5 to 18 becquerels per kilogram with an average of 7 becquerels per kilogram.

“The higher concentrations in spinach arise because the large leaf area of this vegetable is effective in intercepting any contaminants that are deposited from the atmosphere. Leafy green vegetables and milk may be expected to show the highest initial levels of radioactivity immediately after a nuclear accident; concentrations in milk may reach a peak several days after radioactivity is initially deposited onto pasture.

“In the aftermath of a nuclear accident, action to prevent distribution of foodstuffs in Europe is governed by agreed Community Food Intervention Levels (CFILs). The relevant CFILs are:

“So, in the UK and Europe, distribution of milk and spinach (but not leeks) would be restricted, on the basis of the high concentrations of iodine-131.

“To give a perspective on the hazard involved, let’s assume an individual were to consume these foods at a higher than normal rate – taken to be the 97.5th percentile of individual consumption rates in the UK. Further, assume that spinach is consumed at the relevant rate for all green vegetables. The radiation dose accumulated each day for consumption at these rates would be:

“Most of this dose arises from iodine-131; the higher dose calculated for a one year old infant reflects both an assumed high rate of milk consumption (nearly one litre a day) and also a greater accumulation of iodine in the infant thyroid gland.

“Concentrations of iodine-131 in food may be expected to decline rapidly due to its short radioactive half-life. Caesium-137 concentrations may also decline rapidly as the initial deposit is washed off foliage and becomes bound to minerals in the soil.

“Some idea of the scale of the release involved may be gained by noting that substantially higher peak concentrations of caesium-137 in milk were seen in parts of the UK after the Chernobyl accident; peak concentrations of iodine-131 in the UK were a substantial fraction of the average concentrations reported here for Fukushima prefecture.”

Dr Jim Smith, Reader in Environmental Physics, University of Portsmouth said:

“The release of measurements of radionuclides in food is a very significant development because it gives us an indication of the scale of release from the reactor. As many scientists were expecting last week, these results confirm that has been a very serious release of radioactivity from the Fukushima plant. It seems that the radioactive iodine concentrations in some foodstuffs in some areas are very high and there is also an indication of significant radiocaesium release. This doesn’t mean that consumption of these products is necessarily an immediate threat, as limits are set so that foodstuffs can be safely consumed over a fairly long period of time. Nevertheless, for foodstuffs which are found to be above limits, bans on sale and consumption will have to be put in place in the affected areas. A key problem for the Japanese will be the large-scale monitoring this requires, particularly in the current situation. Iodine-131 has a half life of about 8.1 days, so I wouldn’t expect these bans to last more than a few weeks, perhaps up to 2-3 months if the levels are very high. But, if land and foodstuffs are significantly contaminated with Caesium-134 and -137, this would be a much longer-term problem.

“It has been known for a long time that a key route of contamination of people after a nuclear accident is ingestion of radioactive iodine (I-131) in contaminated milk. Because non-radioactive iodine is needed to produce a thyroid hormone, almost all of the iodine you eat goes directly to the thyroid, so ingestion of I-131 carries a risk of developing thyroid cancer in later life. After the 1957 Windscale accident in the UK, a ban was placed on consumption of milk and this has been shown to have significantly reduced the health impact from this accident. Unfortunately, after Chernobyl, there wasn’t a systematic distribution of potassium iodide tablets (to block I-131 uptake by the thyroid) nor was there an effective ban on milk consumption. The increased incidence of thyroid cancer seen in people who were children at the time of the Chernobyl accident could have been significantly reduced if more effective countermeasures had been taken.

“In the initial period after a nuclear fallout, radioactivity is deposited on grass and crops: leafy vegetables such as spinach are particularly vulnerable because the edible leaf surface becomes contaminated. Subsequent (radioactively “clean”) rainfall can wash off much of the surface contamination into the soil where it is absorbed by soil particles. In the longer term, plant roots absorb radioactivity from the soil, generally at much lower levels than are seen initially.”

For more information

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