Caesium-137 alienation around the Chernobyl nuclear power plant. Together with caesium-134, iodine-131, and strontium-90, caesium-137 was among the isotopes distributed by the reactor explosion that constitute the greatest risk to health. The mean contamination of caesium-137 in Germany following the Chernobyl disaster was 2000 to 4000 Bq/m. This corresponds to a contamination of 1 mg/km of caesium-137, totaling about 500 grams deposited over all of Germany. In Scandinavia, some reindeer and sheep exceeded the Norwegian legal limit (3000 Bq/kg) 26 years after Chernobyl. As of 2016 the Chernobyl caesium-137 has decayed by half, but could have been locally concentrated by much
Fukushima Daiichi nuclear disaster Cs in the fish caught were not lower than immediately after the disaster. On 26 October 2012, TEPCO admitted that it could not stop radioactive material entering the ocean, although emission rates had stabilized. Undetected leaks could not be ruled out, because the reactor basements remained flooded. The company was building a 2,400-foot-long steel and concrete wall between the site and the ocean, reaching below ground, but it would not be finished before mid-2014. Around August 2012 two greenling were caught close to shore. They contained more than 25,000 becquerels (0.67 millicuries) of caesium-137 per kilogram (), the highest measured