Washing of the spinach with water by the Nishizawa method resulted in the removal of about 13 ± 2% of the 131I and 45 ± 20% of the 134Cs and 137Cs. Removal rates of 131I of approximately 76 ± 3% after further washing with 1.2 wt% Na2S2O4 for 2 days and 47 ± 2% washing with 10 wt% Na2S2O4 for 2 days were obtained. These values agreed with the dissolution rates of 131I in the liquid used for washing within 2 to 3% error. The removal rates of 134Cs and 137Cs after washing with 1.2 wt% Na2S2O4 for 2 days were 69 ± 47% and 100 ± 52%, respectively, which were in poor agreement with the corresponding dissolution rates. The removal rate of 131I after brief washing with 10 wt% Na2S2O4 was negligible and the dissolution rate was 5 ± 2%. The removal rates of 134Cs and 137Cs for 10 wt% Na2S2O4 increased from 26 ± 11% to 42 ± 11% and from 30±20% to 42 ± 20% after washing with Na2S2O4 for 2 days. The high removal rates in 1.2 wt% Na2S2O4 may be due to the effective reduction of the I2 on the surface of the leaves by Na2S2O4 (1.2 wt%) during the 2 day immersion, which occurred without the bleaching of the leaves and stalks, which occurred in the case of 10 wt% Na2S2O4.
At a location in the central mountain area of the Chugoku region (Bihoku area), concentrations of 131I, 137Cs and 134Cs in rain and air dust were measured before and after the Tohoku-Pacific Ocean Earthquake that occurred on 11 March 2011. Rainwater was also sampled at a location near the Inland Sea. The rainwater was dried on a Naflon sheet. Airborne particles were collected using an air dust sampler. A pure Ge detector shielded by lead blocks was used to measure the gamma rays from the samples. In both locations of the Chugoku region, initial detections of 131I in rainwater occurred on 8 April 2011. On this date, the 131I concentrations in rainwater were 0.23 ± 0.03 Bq/kg in the mountain area and 0.19 ± 0.01 Bq/kg near the Inland Sea. The concentrations of radioactive cesium in rainwater were high from 19 April to 23 April 2011, and were 0.12 ± 0.02 Bq/kg of 134Cs and 0.12 ± 0.03 Bq/kg of 137Cs at maximum, respectively. The atmospheric concentration of 131I was 9 ± 2 mBq/m3 at maximum (6 April 2011), which was estimated without evaluating the 131I activities of the gaseous molecules that passed through an ordinary filter used in the air dust sampler. Maximum concentrations of 134Cs and 137Cs on 7 April 2011 were 10.2 ± 1.3 mBq/m3 and 9.7 ± 1.4 mBq/m3, respectively. Few radioactive cesium and iodine were observed in March. Western and northwestern winds in March probably prevented these artificial radioactive materials from the Fukushima Daiichi Nuclear Power Plant from reaching the mountain area of the Chugoku region.
Distribution of radioactive Cs was investigated in the surface soils of urban and vicinity areas of Shizuoka city, Japan. Concentration of 134Cs and 137Cs showed values in the range of 37 to 2435 Bq/m2 (1 to 95 Bq/kg) and 57 to 2242 Bq/m2 (2 to 98 Bq/kg), respectively. The original production ratio of 134Cs and 137Cs was estimated to be 1:1. The high activity areas were mainly observed along the Warashina area and southern slope of the Udo Hills. The pollutant fine particles with radioactive Cs released from the Fukushima Dai-ichi nuclear power plant were arrived at Shizuoka city by northwest wind in the morning and southwest wind in the afternoon on March 15, 2011. The radioactive Cs distribution pattern indicates that these pollutant particles were dropped on land surface of the Warashina area and southern slope of the Udo Hills during ascending wind in the afternoon on March 15, 2011.
We examined the characteristics of the radioactive contamination and the physical removal of radioactivity from contaminated cabbage and spinach. In a distribution imaging study, there were two types of contamination, spot type and spread type, of cabbage and spinach. The relative radioactivity (PSL) of the face of the leaf was much higher than that of the back of a leaf of cabbage. The ratio of relative radioactivity (PSL) between spot contamination and spread contamination in a leaf of spinach was 9.4% and 90.6%, respectively. More than 80% of radioactivity attaches to the surface of leaves of spinach. There was no significant difference of radioactivity removal between hand-washing and rinsing with running water. The degree of removal of radioactivity from contaminated spinach depended on the length of time between contamination and rinsing. When contaminated spinach was rinsed within 1 week after contamination, the removal ratio of 131I and 137Cs was high, with 50% and 70%, respectively. When rinsing contaminated spinaches more than 2 weeks after contamination, the removal ratio of 131I and 137Cs was low, approximately 34% and 69%, respectively.
We examined a simple and effective removal method for contaminated farm products to ensure the relief of farmers and the security of consumers. Removal of radionuclides from spinach by chemical methods was investigated. The result of chemical removal showed that antioxidant agents removed radionuclides from spinach by 70–80% for 131I and more than 80% for radiocesium. In particular, ascorbic acid is promising as a safe and versatile option.