167
2.1 Correlations Between Th and U Concentrations
in Nonagricultural Soil Samples
Previously, we used init U/Th = 0.23 (Tagami and Uchida 2006) based on some nonagricultural soil U/Th ratios; we did a further data survey to get a more reliable init U/
Th ratio in soil (nonphosphate fertilizer affected). For this purpose, it is better to use
nonagricultural soil data. We selected
232
Th and
238
U activity concentrations in nonagricultural soil samples from Environmental Radiation Database (NRA 2018) if
these two radionuclides were measured in the same soil sample collected at the
same sampling time. We converted the database values of radioactivity concentrations (Bq kg
−1
-dry) into mass concentrations (mg kg
−1
-dry) by multiplying Th activity concentrations by 0.246 mg Bq
−1
and U activity concentrations by 0.0804 mg Bq
−1
before finally calculating 154 U/Th concentration ratios.
A further literature survey allowed us to add more U and Th concentration data
from 54 samples (Mizohata et al. 1977; Terashima et al. 2004; Kano et al. 2009;
Sahoo et al. 2011, 2013) and one U/Th ratio (Takeda et al. 2006). In total, 210 samples with U/Th data for nonagricultural soil samples from 21 out of 47 prefectures
in Japan were collected. The correlation of U and Th concentrations in the collected
nonagricultural soil samples is plotted in Fig. 3. We found a high correlation factor
of R = 0.873 (p < 0.001) just as found for river sediment samples. Thus, generally,
Th and U should be correlated well in soil, but in agricultural fields, they were not.
The obtained U/Th data are summarized in Table 1. The data is distributed lognormally (Fig. 4), and the distribution was narrow; therefore, the geometric mean
(GM) value of the U/Th ratio was calculated. Yamagata and Iwashima (1967) and
Minato (2005) also reported Th and U concentrations in nonagricultural soil samples in Japan so that their results are listed in the same table, too. For the data by
Yamagata and Iwashima (1967) and Minato (2005), we simply calculated the GM
Fig. 3 Correlation
between concentrations of
U and Th in
nonagricultural soils
Soil-to-Crop Transfer Factor: Consideration on Excess Uranium…
2.1 Correlations Between Th and U Concentrations
in Nonagricultural Soil Samples
Previously, we used init U/Th = 0.23 (Tagami and Uchida 2006) based on some nonagricultural soil U/Th ratios; we did a further data survey to get a more reliable init U/
Th ratio in soil (nonphosphate fertilizer affected). For this purpose, it is better to use
nonagricultural soil data. We selected
232
Th and
238
U activity concentrations in nonagricultural soil samples from Environmental Radiation Database (NRA 2018) if
these two radionuclides were measured in the same soil sample collected at the
same sampling time. We converted the database values of radioactivity concentrations (Bq kg
−1
-dry) into mass concentrations (mg kg
−1
-dry) by multiplying Th activity concentrations by 0.246 mg Bq
−1
and U activity concentrations by 0.0804 mg Bq
−1
before finally calculating 154 U/Th concentration ratios.
A further literature survey allowed us to add more U and Th concentration data
from 54 samples (Mizohata et al. 1977; Terashima et al. 2004; Kano et al. 2009;
Sahoo et al. 2011, 2013) and one U/Th ratio (Takeda et al. 2006). In total, 210 samples with U/Th data for nonagricultural soil samples from 21 out of 47 prefectures
in Japan were collected. The correlation of U and Th concentrations in the collected
nonagricultural soil samples is plotted in Fig. 3. We found a high correlation factor
of R = 0.873 (p < 0.001) just as found for river sediment samples. Thus, generally,
Th and U should be correlated well in soil, but in agricultural fields, they were not.
The obtained U/Th data are summarized in Table 1. The data is distributed lognormally (Fig. 4), and the distribution was narrow; therefore, the geometric mean
(GM) value of the U/Th ratio was calculated. Yamagata and Iwashima (1967) and
Minato (2005) also reported Th and U concentrations in nonagricultural soil samples in Japan so that their results are listed in the same table, too. For the data by
Yamagata and Iwashima (1967) and Minato (2005), we simply calculated the GM
Fig. 3 Correlation
between concentrations of
U and Th in
nonagricultural soils
Soil-to-Crop Transfer Factor: Consideration on Excess Uranium…