Monitoring of Radioactive Substances in Foods Distributed in Kyoto, Japan (1991–2011): Comparison of Detection Rates and Concentrations before and after the Fukushima Daiichi Nuclear Power Plant Accident

Since the Chernobyl Nuclear Power Plant accident, radioactive substances have been continually monitored in foods collected in the city of Kyoto, Japan. The importance of the monitoring was increased by the Fukushima Daiichi Nuclear Power Plant accident in March 2011. Here, the detection rates and concentrations of radioactive substances were compared among food samples collected before and after the accident in Fukushima prefecture. Before the accident, 137Cs was the only radioactive substance detected in foods. The detection rate was 70% for fish and shellfish samples and the highest concentration was 1.7 Bq/kg. It was also 83% for fresh mushroom samples and the highest concentration was 7.5 Bq/kg. In contrast, the detection rate was low for vegetables and the concentrations were also lower than those of the above samples. On the other hand, after the accident, 131I was detected in food produced in the Tohoku and Kanto areas. Actually, 131I (3,400 Bq/kg), 134Cs (280 Bq/kg), and 137Cs (280 Bq/kg) were detected in mizuna, a leaf vegetable, on March 23, 2011. These radioactive substances were detected in all leaf vegetable samples examined in March and April 2011, but they were not detected in samples examined in November 2011. 131I was not detected in any food sample examined after May 2011. However, 137Cs (average=7.9 Bq/kg) was consistently detected in fish and shellfish samples until November, although the concentrations were less than the regulatory limits. It appears unlikely that foods containing radioactive substances over the regulatory limits are currently being distributed in Kyoto.