Internal Exposure

5.2.2.1 Targets and Methods

Local governments were strongly encouraged to monitor the specific radioactivity (Bq kg−1, becquerels per kilogram) of local food and drinking water under the present popular policy of “Local Production for Local Consumption” in Japan.

Fig. 5.1 Annual average dose at schools in Kashiwa City measured by personal dose meters from September 1, 2011 to August 31, 2012. Kashiwa City is located in the northwest part of Chiba Prefecture in the metropolitan area of Tokyo, Japan, roughly 200 km to the south of the TEPCO Fukushima Dai-ichi Nuclear Power Plant

In parallel with the national survey and the relating prefectures' survey, the three cities have been continuing to monitor various materials and to announce the results to their citizens. The target materials are school lunch and food items, local food items, tap water, and supplied water, water in school or public pools, waste disposal, etc. For example, the actual lunch supplied for 1 week in each school was monitored by a Ge semiconductor or NaI(Tl) scintillation spectroscopy system.

The sampling procedures of local food items are as follows: for example, in Kashiwa City, (1) the types of food to be monitored from the representative four areas of the city are discussed and selected among agricultural cooperatives, farmers, and city officers; (2) city officers ask the selected farmers for basic information on these food items, for example, the planting season; and (3) local food items are sampled, weighed, and passed on to monitoring rooms. The food samples are then measured by a NaI(Tl) scintillation spectroscopy system (a 15-min measurement with a 500-ml Marinelli beaker, where the minimum detectable limit concentration

Table 5.2 Specific radioactivity of service water in Nagareyama purification plant in April, 2011

–, no data

ND, less than lower detectable limit concentration

is estimated as 6 Bq kg−1). As of the end of August 2012, about 800 local food samples have been monitored using this procedure in Kashiwa City. These data have been reported on the city website as well as in a bimonthly report in the public relations magazine of the local government.

Nagareyama City and Bunkyo ward have also monitored their food materials and opened all data to the public similarly.

5.2.2.2 Data and Information

The following data are major results of activities conducted by the three local governments as described in the earlier section.

The specific radioactivity of the drinking water and of the local food items has been surveyed since March 2011 and since April 2011, respectively, for example in Nagareyama City. As of March 23, 2011, only one sample of service water showed 110 Bq kg−1 of 131I; no water sample other than this has been found to exceed the limits until now, 2013, as shown in Table 5.2.

The highest specific radioactivity was 831 Bq kg−1 of 134+137Cs, measured for a flat Japanese mushroom that was cultivated on Japanese oak logs, which were sampled in Nagareyama City on November 16, 2011. This was detected during the monitoring carried out for Chiba Prefecture. In addition, the radioactivity levels of an outdoor bamboo shoot and a flat mushroom also temporarily exceeded the acceptable limits for the specific concentration of food items. These were also detected by Chiba Prefecture. According to the monitoring results for Nagareyama City, disaster-induced specific radioactivity of all surveyed food items (excluding the items listed above) was found to be below the limits for intake dose (see Tables 5.3 and 5.4).

In Kashiwa City, about 800 samples of the local food items, which were grown and circulated in the city as of the end of August 2012, have been checked using a NaI(Tl) scintillation spectroscopy system. An outdoor bamboo shoot sampled in the city on April 9, 2012 showed 170 Bq kg−1 as the specific radioactivity of 134+137Cs. In addition, a crucian carp sampled in Teganuma Lake on June 23, 2012 showed 241 Bq kg−1. Specific radioactivity of all surveyed samples, other than these three, has been below the limits.

In Bunkyo ward, no water sample supplied to the city has exceeded the national limits for intake dose, based on the monitoring at their local purification plants. The specific radioactivity of school lunches was also surveyed four times (in December

Table 5.3 Specific radioactivity (134+137Cs) of local food items in Nagareyama City, measured after April 13, 2012

This monitoring was carried out by the Nagareyama City local government

Table 5.4 Specific radioactivity (134+137Cs) of local food items in Nagareyama City, measured before April 13, 2012

This monitoring is carried out by the Nagareyama City local government

2011, and May, July, and September 2012) by the local government. Thus far, 162 sets of school lunches in the city have been checked using a Ge spectroscopy system. The highest specific radioactivity of 134+137Cs was detected as 2.5 Bq kg−1 in a school lunch and 15.4 Bq kg−1 in milk, which were recorded in December 2011.