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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