3.1.2. 137Cs and 134Cs Levels after the FDNPP Accident

We obtained 42 TDS samples from Sendai City, Fukushima City, and Tokyo in October and November of 2011, approximately six months after the FDNPP accident. According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) [21], the total release of 137Cs, 134Cs, and 131I in the atmosphere resulting from the FDNPP incident was estimated to be 8.8 PBq, 9.0 PBq, and 124 PBq, respectively. Immediately after the FDNPP accident, some foodstuffs, such as spinach and milk, were highly contaminated with 131I, which accumulates in the thyroid gland and may increase the risk of thyroid cancer [22–24]. However, 131I levels decreased rapidly and became undetectable [25–27], owing to its short half-life of 8.02 days. Therefore, 131I was not observed in the present study.



for each food group. \*5 This food group was categorized as "Seasonings and beverages" in 2006. \*6 This food group was categorized as "Others" in 2006.

Cesium-134 was not detected in any of the TDS samples between 2006 and 2010, but was observed in all food groups, with the exception of "fats and oils", in 2011 as a consequence of the FDNPP accident. Table 2 shows the 137Cs and 134Cs activity concentration of the TDS samples after the FDNPP accident. The detection rates of 137Cs and 134Cs were 88% and 69%, respectively. No sample exceeded the 137Cs level of 0.1 Bq/kg during 2006 to 2010, whereas 19 samples exceeded this level in 2011. The activity concentrations of 137Cs (Bq/kg) were in the range of <0.041–6.400 in Sendai City, <0.089–4.100 in Fukushima City, and <0.045–2.100 in Tokyo; while those of 134Cs (Bq/kg) were <0.011–5.400 in Sendai City, <0.040–3.500 in Fukushima City, and <0.025–1.700 in Tokyo. The activity concentration ratios of 134Cs to 137Cs in the TDS samples were ranged from 0.38 to 0.94, and the mean and standard deviation values were calculated to be 0.73 and 0.14, respectively.

The highest activity concentration of radioactive Cs (137Cs + 134Cs) among the 42 TDS samples was 12 Bq/kg, and found in the "milk and dairy products" group from Sendai City. This food group also showed the highest Cs activity concentration in Tokyo (3.8 Bq/kg), while fruits carried the highest activity concentration in Fukushima City (7.6 Bq/kg). Cs activity concentrations in the fruits of Fukushima City were characteristically higher than those in Sendai City (0.093 Bq/kg) and Tokyo (0.17 Bq/kg). Although "green and yellow vegetables", such as spinach, showed extremely high Cs activity concentrations, with values exceeding 10,000 Bq/kg immediately following the FDNPP accident, their levels declined rapidly [26–28]. Thus, Cs activity concentrations in "green and yellow vegetables" were at most 0.58 Bq/kg in our TDS samples. The "meat and eggs" group was found to have higher Cs activity concentration before the FDNPP accident, while the relatively low activity concentration after the accident is due to the import of animal feed from foreign countries. Interestingly, 137Cs and 134Cs were not found in any "fats and oil" samples before or after the accident. This may be due to their poor solubility in lipids.

After the FDNPP accident, regulation of the levels of radionuclides in food was established by the MHLW. On 17 March 2011, the provisional regulation value (RPV) for radioactive Cs was established to be 200 Bq/kg for "drinking water" and "milk and dairy products", and 500 Bq/kg for vegetables, grain, meat, eggs, and fish [28,29]. Presently, the standard limits, which were put into place on 1 April 2012, are 100 Bq/kg for general foods, 50 Bq/kg for milk and infant foods, and 10 Bq/kg for drinking water [30,31]. In the present study, although Cs activity concentrations of the TDS samples increased significantly after the FDNPP accident, the concentrations were well below the regulatory levels. The highest radioactive Cs value of 12 Bq/kg in this TDS was 17 times lower than the RPV for "milk and dairy products", and four times lower than the standard limit for milk.
