20 September 2020
The fact that the concentration of cesium, a radioactive substance dissolved in seawater along the coast of Fukushima Prefecture, temporarily increased by 4.3 times due to Typhoon No. 19 last fall was a specially appointed associate professor at the Fukushima University Institute for Environmental Radioactivity (Ocean). It was found in the investigation by (Chemistry) et al. Sediment runoff due to heavy rain seems to be one of the causes.
The research group collected seawater from June to October last year at a total of 25 locations near the mouth of rivers such as Tomioka Town and Iwaki City, along the coast, and offshore, and investigated the cesium concentration. In October after the typhoon passed, the average concentration at three locations near the mouths of the Tomioka, Natsui, Same, and Hikita rivers was 39 millibecquerels per liter, which was much higher than the average of 9 millibecquerels from June to September.
Cesium is attached to the sediment deposited on the bottom of the river. Associate Professor Takada analyzed that the record heavy rain caused by the typhoon caused sediment to flow out of the river into the sea, and cesium was dissolved in response to potassium ions in the seawater. It is estimated that about 30% of the increase in concentration is due to this mechanism.
Associate Professor Takada said, “Although there is a study that the amount of cesium discharged from the Fukushima Daiichi Nuclear Power Plant is decreasing year by year, there are many unclear points about the increase in concentration derived from typhoons. Collect data and dispel rumors. I want to connect to. “
The research was published in a magazine published by the Chemical Society of America in early August.