Abstract
Sumida and Ohta wards in Tokyo and Shobara City in Hiroshima are approximately 220 km, 238 km and 775 km away from the Fukushima Daiichi Nuclear Power Plant (FDNPP), respectively. Drinking water (DW) samples were obtained from the taps at these three locations during the period from late March 2011 until early March 2013. The concentrations of the 131I, 134Cs and 137Cs activities in the DW samples have been measured. The radioactive cesium (Cs) concentration at Sumida ward had decreased until the end of 2011, and showed a repeated trend of increase and decrease afterward. During the early period after the Great East Japan Earthquake, the 131I concentration had more acutely decreased at Sumida ward. On 3 April 2011, the 131I concentrations in the DW samples at Sumida and Ohta wards agreed with each other within uncertainty. The radioactive Cs concentration at Ohta ward has tended to be less than that at Sumida ward during the two-year period. In Shobara, the 131I concentration in a DW sample on 7 April 2011 was possibly greater than 0.01 Bq/kg. This implies that the 131I activities included in air dusts and rain might have entered into the river water in Shobara in early April 2011. The radioactive Cs concentrations in the six DW samples at Shobara City during the period from 24 March 2011 to3 March 2013 were regarded as zero within uncertainty ranging from 0.001 Bq/kg to 0.007 Bq/kg.
