環境

Based on the results of “Behavior analysis of radioactive cesium in sediment sampled at Tamagawa River Watershed for 30 years later”, radioactive cesium in river water and sediments sampled at 50 points in Tamagawa River watershed, concluding main and tributary stream, were measured for behavior analysis in December 2017.

Furthermore, seasonal variation in the concentration of radioactive cesium in rivers was observed by conducting quarterly surveys at 25 selected locations.

Dissolved and suspended cesium concentration in the present Tamagawa River watershed exists in very low order.

The dissolved cesium was detected from Lake Okutama and the upper tributaries.

The concentrations of radioactive cesium in sediments sampled at the tributaries and lower main stream were high compared to upper and middle main stream.

Monitoring result suggested that Lake Okutama and the tributaries are considered to be one of the sources of radioactive cesium to the mainstream.

Considering the concentration distribution of radioactive cesium in rivers and chemical analysis of sediment samples, it is estimated that radioactive cesium is accumulated in Lake Okutama and upper tributary basin.

Kenta Hagiwara