After the Chernobyl nuclear power plant accident, relatively high radioactive cesium levels were detected in various mushrooms produced in many countries. Mushrooms have a high transfer factor, showing a relatively high uptake of cesium from wood and soil from which they grow.
In the present investigation, we analysed radioactive cesium concentrations contained in the dried Lentinula edodes (Shiitake) produced in various prefectures all over Japan, and examined the effectiveness of this mushroom as an indicator of radioactive contamination of environment due to nuclear explosion tests and Chernobyl power plant accident.
We collected dried Lentinula edodes (Shiitake) grown on the wood from 32 prefectures from north to south, and measured ¹³⁷Cs and ¹³⁴Cs concentrations with high purity Ge-detectors. Levels of ¹³⁷Cs concentration were found to vary from 3.4 to 33.6 Bq/kg, while those of ¹³⁴Cs were less than detectable.
¹³⁷Cs concentrations in Lentinula edodes (Shiitake) samples showed a statistically significant positive correlation with those in rain and dry fallout at 1% significance level. They also proved to have been inversely correlated with atmospheric temperature at 10% significance level, but it could not be determined whether it was only an apparent correlation or not because no information of ¹³⁷Cs concentrations in wood was available. Multiple correlation coefficient of ¹³⁷Cs concentrations with atmospheric temperatures and fallout levels was 0.54 which was statistically significant at 2.5% level. A variance analysis based on the ¹³⁷Cs concentrations in Lentinula edodes (Shiitake) classified into 7 groups (Hokkaido-Tohoku, Kanto, Chubu, Kinki, Chugoku, Shikoku and Kyushu) showed that the variance between the groups was significantly greater than that within each group, which suggested, together with the above-mentioned information regarding the correlation of ¹³⁷Cs concentration in Lentinula edodes (Shiitake) with average temperatures and fallout levels, that the ¹³⁷Cs levels in Lentinula edodes (Shiitake) are possibly related with these two factors.