Distribution of 137Cs in Environmental Soil and Crude Drugs

Radioactivity of 137Cs and 40K was determined on commercially available products of Houttuynia Herb which were imported from China and Taiwan or processed in Japan, and of Houttuynia cordata harvested in 15 places in Japan and the surrounding soil. On Houttuynia Herb, the concentrations of 137Cs and 40K were LTD (less than detectable)-7.6 Bq/kg dry and 743-1964 Bq/kg dry, respectively, suggesting that the concentration of 137Cs was less than 1% of that of 40K. The domestic products were found to contain higher concentrations of 137Cs and 40K than the imported ones. The concentration of 137Cs of Houttuynia cordata harvested in Japan ranged from 0.8 Bq/kg dry to 172 Bq/kg dry, while the concentration of 40K was almost the same as that of the commercial products. The concentration ratio of 40K in Houttuynia cordata to that in the soil was correlated with the moisture content and the ignition loss of the soil. However, the concentration ratio of 137Cs did not show a very clear correlation. When 15 g of Houttuynia Herb or Houttuynia cordata was daily decocted and given for 1 year the former showed the committed dose equivalent of 0.02-0.5 μSv and the latter 0.06-12 μSv. Both of these values were less than 0.5% of the annual effective dose equivalent from the nature, 2.4 mSv.