According to Miyagi prefecture, 86 Bq/Kg of Iodine-131 was measured from sewage sludge in Iwanuma city Miyagi.
Iodine-131 is from nuclear reaction or medical treatment.
The sample was collected from 10/23 to 10/25/2012.
https://www.r-info-miyagi.jp/site/wp-content/uploads/2012/11/happyou1102.pdf
Iori Mochizuki