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 On 13 February 2014, TEPCO reported 37 kBq (1.0 microcurie) of caesium-134 and 93 kBq (2.5 microcuries) of caesium-137 were detected per liter of groundwater sampled from a monitoring well. Dust particles gathered 4 km from the reactors in 2017 included microscopic nodules of melted core samples encased in caesium. After decades of exponential decline in ocean caesium from weapons testing fallout, radioactive isotopes of caesium in the Sea of Japan increased after Fukushima from 1.5 mBq/L to about 2.5 mBq/L and are still rising as of 2018, while those just off the western coast of Japan have declined. According