Uncertainty as to the Risk of Contamination

The winds turn and uncertainty persists concerning the risks of contamination of Japanese populations. Since the authorities have not yet communicated the figures for the composition and quantities of ejection of radioactive substances, only independent estimates and measures can give an appreciation of the situation. Yesterday, after the winds turned inland, the independent commission for research and information on radioactivity (CRIIRAD), openly alarmist, reported a peak of activity of iodine 131 in Tokyo. On Sunday morning its activity climbed to 15.6 Becquerels per cubic meter, compared with 0.1 Bq/m3 on Saturday. This level decreased to 8 Bq/m3 at 14h. These measures were made by a Tokyo institute, assures the CRIIRAD.

This organization also denounces the contamination of spinach and of milk, at levels more dangerous than the Japanese authorities have let it be understood. On Saturday the authorities spoke only of "traces" of radioactivity. But, "on samples of spinach collected on 18 March in Hitachi [1] the activity of iodine 131 is 54100 Bq/kg", emphasizes the CRIIRAD. "It suffices for a young child to ingest 103g, a child of 5 years of age to ingest 185g, or an adult, 840g in order to reach, in a single meal, the annual limit fixed in Japan of 2000 Bq/kg."

On Monday the World Health Organization wished to be less alarmist. According to them, foodstuffs exposed "briefly" to radiation in Japan can be consumed. The organization recognizes, however, that the discovery of food contaminated at a distance of 120 km from the power plant was unexpected, so the Japanese government acted correctly, on Monday, by withdrawing these crops from the markets.

It is difficult, then, to obtain a clear idea of the situation. For a week, now, the Institute for Radiological Protection and Nuclear Security (IRSN, a French public surveillance organization) has constructed models for trying to evaluate the level of exposure of the local populations. According to their projections, the levels of damaging exposures (50 millisieverts per hour for a child of 1 year of age, permanently exposed) will be present only in a circle of radius 20 km about Fukushima. This does not exclude an impact in a larger area. Traces of iodine in the water in Tokyo, a net increase in radioactivity in a village situated at 40 km from the power plant, such examples indicate that the outcome will not be negligible.

"However the situation develops, Japan will have to manage, over the long term, deposits of radioactivity due to these ejections," adds the French Nuclear Safety Agency (ASN).

One thing, however, seemed certain yesterday: the radioactive cloud expected over France, tomorrow [2], according to the projections of the IRSN, should not present any danger. Diluted, the radioactivity will not exceed 0.001 Bq/m3. In comparison, after Tchernobyl, the values measures in France were of the order of 1 to 10 Bq/m3.