2011 Tōhoku earthquake and tsunami
It was reported that radioactive iodine was detected in the tap water in Fukushima, Tochigi, Gunma, Tokyo, Chiba, Saitama, and Niigata, and radioactive caesium in the tap water in Fukushima, Tochigi and Gunma. Radioactive caesium, iodine, and strontium were also detected in the soil in some places in Fukushima. There may be a need to replace the contaminated soil. Many radioactive hotspots were found outside the evacuation zone, including Tokyo. Food products were also found contaminated by radioactive matter in several places in Japan. On 5 April 2011, the government of the Ibaraki Prefecture banned the fishing of sand lance after discovering that this species was contaminated by radioactive caesium above legal limits. As late as July 2013 slightly elevated levels of radioactivity were found in beef on sale at Tokyo markets.
Isotopes of iodine
Iodine-135 is an isotope of iodine with a half-life of 6.6 hours. It is an important isotope from the viewpoint of nuclear reactor physics. It is produced in relatively large amounts as a fission product, and decays to xenon-135, which is a nuclear poison with a very large thermal neutron cross section, which is a cause of multiple complications in the control of nuclear reactors. The process of buildup of xenon-135 from an accumulated iodine-135 can temporarily preclude a shut-down reactor from restarting. This is known as xenon-poisoning or "falling into an iodine pit".