All four reactors immediately shut down on Friday after the earthquake, but the reactor cores have not cooled, in part because pumps that were meant to drive water into the reactors failed. The reactors overheated and turned the water into steam, which in turn built up pressure.
Engineers had to release some of the steam — also releasing some radioactive caesium and iodine into the air. Amid explosions and fears of meltdowns, here’s what we know about potential threats to human health:
1. One major concern is exposure to radioactive iodine. If iodine is absorbed by the thyroid gland it leads to an increased risk of thyroid cancer. The Japanese government has handed out iodine pills because they can decrease the risk of the radioactive form being absorbed. The real worry is not inhaled iodine, though it’s the possibility of iodine contaminating dairy supplies.
2. To be cautious, Japanese authorities have evacuated people in the immediate area — we already know that some, including members of clean-up crews are thought to have radiation poisoning.
3. At greatest risk are little kids and fetuses, because children have such rapidly dividing cells, connecting brain regions, and growing bodies (including their little radiation-sensitive thyroid glands) that the potential for impact is exponential.
4. The World Health Organization has said that the public health risk is “quite low,” as the radiation levels outside the plants have remained at safe levels. The Chernobyl incident caused an epidemic of thyroid cancer, but the radiation levels in Japan at this point seem to be close to one million times lower, according to The New York Times.
5. Iodine has a short half-life, but the possible release of caesium is a bigger worry, because the half life is 30 years. Japan continues to work at cooling the plants and containing all forms of radioactive material.