Friday, November 23, 2012

On Rice Contamination in Japan: Samples Dated Sep 29, 2011

Paddy-field contamination with 134Cs and 137Cs due to Fukushima Dai-ichi Nuclear Power Plant accident and soil-to-rice transfer coefficients Satoru Endo*, Tsuyoshi Kajimoto, Kiyoshi Shizuma Journal of environmental Radioactivity 116 (2013) 59e64

[Abstract] The transfer coefficient (TF) from soil to rice plants of 134Cs and 137Cs in the form of radioactive deposition from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011 was investigated in three rice paddy fields in Minami-Soma City. Rice crops were planted in the following May and harvested at the end of September.

Soil cores of 30-cm depth were sampled from rice-planted paddy fields to measure 134Cs and 137Cs radioactivity at 5-cm intervals. 134Cs and 137Cs radioactivity was also measured in rice ears (rice with chaff), straws and roots.

The rice ears were subdivided into chaff, brown rice, polished rice and rice bran, and the 134Cs and 137Cs radioactivity concentration of each plant part was measured to calculate the respective TF from the soil. The TF of roots was highest at 0.48 _ 0.10 in the field where the 40K concentration in the soil core was relatively low, in comparison with TF values of 0.31 and 0.38 in other fields.

Similar trends could be found for the TF of whole rice plants, excluding roots. The TF of rice ears was relatively low at 0.019e0.026. The TF of chaff, rice bran, brown rice and
polished rice was estimated to be 0.049, 0.10e0.16, 0.013e0.017 and 0.005e0.013, respectively

Excerpts from paper:

This paper presents our findings on the measured radioactivity of soil cores and rice plants and discusses the TF of radioactivity from the soil to rice plants....

The TF, which was first introduced by Myttenaere (1972), is a useful tool for estimating the radioactivity concentration in plants to determine the contamination density in the soil. The TF from the soil to rice plants is defined as the ratio of radioactivity concentration (Bq/kg) of the dried plant (or each part of the plant) to the average radioactivity concentration (Bq/kg) of the dried soil from
the surface to a depth of 15 cm....
In our investigation,we calculated the TF from the soil to rice roots, rice straws and rice ears separately. Similarly, the TF was calculated separately for the chaff, brown rice, polished rice and rice bran.

The radioactivity concentration of the whole rice plant, excluding the roots, was 113e186 Bq/kg for 134Cs and 160e197 Bq/ kg for 137Cs, respectively. Radiocesium concentrations in F3 rice samples were about 1e1.6-fold higher than those of F1 and F2. 

In summary, the TF of 134Cs and 137Cs in rice plants harvested from paddy fields contaminated by the FDNPP accident in 2011 was determined by measuring soil core and rice plant samples. The radiocesium concentration in soil cores and rice plants from paddies irrigated with dam water was 1e1.7-fold higher than that by well groundwater. The dam water might have contained small amounts of contaminated mud. The radiocesium concentration in the soil and/or plants in the paddy fields could have been affected by irrigation with dam water, which might have contained more radiocesium than the groundwater.

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