Satellite image courtesy of GeoEye; graphic by Stephen Shankland/CNET
This illustration, based on GeoEye satellite photo viewed through Google Earth, shows the locations of the six Fukushima Daiichi nuclear reactors. The reactors are about 140 miles northeast of Tokyo.
Last week I wrote a blog post about the radiation dangers in Japan as a result of the problems with the Fukushima reactor. In that article I pointed out that there were spots just outside the 30 km shelter-in-place zone that were receiving significant amounts of radiation. Unfortunately, it would appear the Japanese government is coming to the conclusion that the risks of radiation outside the 30 km zone may be significant.
Now, I did make a mistake in that post: I stated the chances of getting cancer, when indeed the numbers I was giving were the chances of dying from cancer. So, in fact, I was underestimating the cancer risk by a factor of 2.5. For example, with 1 rem of exposure, the chances of getting cancer are 1/1000 (the chances of dying from cancer are 1/2500, although this depends on the cancer survival rate you presume).
This week, the Japanese broadcaster NHK has reported that the government now estimates that people outside the 30 km zone could receive a radiation dose of 10 rem (100 millisieverts). A radiation exposure at that level has a 1/100 (1 percent) chance of inducing cancer during a person’s lifetime. That is a significant risk, and certainly not one I would be willing to take. The article goes on to report that Cabinet Secretary Yukio Endano “cited a lack of data and the need for more precise calculations, and said there is no need for immediate evacuation or to seek shelter indoors.”
I find this last statement somewhat confounding. It is straightforward to estimate the radiation doses that have been received by using the measurements the Japanese Ministry of Education, Culture, Sports, Science and Technology are making available on their website. Simply extrapolating those numbers into the future shows that there are people who will receive significant amounts of radiation if they are not evacuated.
Unfortunately, not all members of society are at equal risk. Children are much more vulnerable to the effects of radiation. This was a clear lesson from the Chernobyl incident, where children who ingested radioactive iodine have shown a very dramatic increase in the incidence of thyroid cancer. That, of course, is why the Japanese government has issued warnings about children drinking Tokyo tap water.
This crisis will continue. One can only hope that the Japanese government will be more proactive in protecting its citizens from long-term health risks. Signs that they are beginning to accept the true scope of the danger appeared earlier today when the government began evacuating people from from the 30 km shelter-in-place zone.
Paul Padley, Ph.D., is a professor of physics and astronomy at Rice University.