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.
Iodine-125
To isolate radioiodine, the irradiated capsule is first cooled (to collect free iodine gas on the capsule sides) and the remaining Xe gas is allowed to escape. The inner walls of the capsule are then rinsed with dilute NaOH solution to collect iodine as soluble iodide and hypoiodite OI, according to the standard disproportionation reaction of halogens in alkaline solutions. Any cesium immediately oxidizes and passes into the water as Cs. In order to eliminate any long-lived Cs and Cs which may be present in small amounts, the solution is passed through a cation-exchange column, which exchanges Cs for another non-radioactive cation. The radioiodine (as anion I or OI ) remains in solution as iodide/hypoiodite.