Whole-body counter surveys of Miharu-town school children for four consecutive years after the Fukushima NPP accident

Abstract

Comprehensive whole-body counter surveys of Miharu-town school children have been conducted for four consecutive years, in 2011-2014. This represents the only long-term sampling-bias-free study of its type conducted after the Fukushima Dai-ichi accident. For the first time in 2014, a new device called the Babyscan, which has a low (134/137)Cs MDA of <50 Bq/body, was used to screen the children shorter than 130 cm. No child in this group was found to have detectable level of radiocesium. Using the MDAs, upper limits of daily intake of radiocesium were estimated for each child. For those screened with the Babyscan, the upper intake limits were found to be ≲1 Bq/day for (137)Cs. Analysis of a questionnaire filled out by the children's parents regarding their food and water consumption shows that the majority of Miharu children regularly consume local and/or home-grown rice and vegetables. This however does not increase the body burden.

Figure 1.

A map of the air dose rate (µSv/h) estimated from airborne monitoring, as of November 19, 2013.¹¹⁾ The locations of the Fukushima Dai-ichi nuclear power plant (FDNPP), the town of Miharu, Fukushima City, Koriyama City, and Hirata Central Hospital (Hirata CH) are indicated.

Figure 2.

The age distribution of the subjects. The gray (pink) bars are for those measured with the Fastscan (Babyscan).

Figure 3.

The distribution of age vs height of the subjects. The subjects shorter than 130 cm were scanned with the Babyscan.

Figure 4.

Weight (kg) vs measured amount of ⁴⁰K (Bq) in the subjects’ body.

Figure 5.

Weight (kg) vs ¹³⁷Cs MDA (Bq/body).

Figure 6.

Weight (kg) vs ¹³⁷Cs MDA (Bq/kg).

Figure 7.

Circles: The equilibrium plateau values of ¹³⁷Cs body burden calculated using Mondal3 software.¹⁵⁾ Curve: interpolating curve, shown with a 1-σ uncertainty band, obtained by fitting a cumulative Gompertz distribution to the Mondal3 outputs.

Figure 8.

Blue (orange) curve: The age dependence of the estimated upper limit of ¹³⁷Cs daily intake, for the detection limit of 300 (50) Bq/body. Gray (pink) dots: upper limits of ¹³⁷Cs daily intake estimated using the actual Fastscan (Babyscan) MDA of the Miharu-town school children.

Figure 9.

Graph showing results of questionnaire concerning water, rice, and vegetable consumption of Miharu families.

Figure 10.

A graphical representation of the result of a correspondence analysis performed on the cross table (Table 2), showing the correlation between the choice of “bottled water” (left) and “well water” (right) with the choice of rice and vegetables. For details, see text. Abbreviations are, AF - avoid Fukushima, BF - buy Fukushima, NC - do not care about the source, Home - local/home, UT - eat untested.