Estimate the contribution of water-derived ¹³⁷Cs in the total ¹³⁷Cs in brown rice using water-to-brown rice transfer parameters and the ratio of ¹³⁷Cs/¹³³Cs

Figures & data

Table 1. Physical and chemical properties of the soils in the pot experiment (mean ± sd, n = 3)

Soil properties	Soils
Soil pH (H2O)	5.4
Soil pH (KCl)	4.4
Exchangeable K (mg kg^−1)	270 ± 10
Cation exchange capacity (cmolc kg^−1 dry soil)	17.6
Total of carbon (mg g^−1)	7.1
Total of nitrogen (mg g^−1)	0.4
Coarse sand (0.2–2.0 mm) (%)	31.8
Fine sand (0.02–0.2 mm) (%)	31.9
Silt (0.002–0.02 mm) (%)	18.7
Clay (< 0.002 mm) (%)	17.6
Soil texture	Sandy Clay Loam (SCL)

Table 2. The concentrations of ¹³⁷Cs and ¹³³Cs in soils, as well as the exchangeable fraction of soils in the pot experiment (mean ± sd, n = 3)

Elements	Soils	Exchangeable fraction
^137Cs (Bq g^−1) dry wt	0.43 ± 0.03	0.0386 ± 0.0005
^133Cs (ng g^−1) dry wt	2910	54 ± 2
^137Cs/^133Cs (Bq ng^−1)	0.00015	0.00072 ± 0.000037

Table 3. The concentrations of cations, ¹³⁷Cs, and ¹³³Cs in water supplied to the pots

Pot experiment	Cations (mg L^−1)					^137Cs (Bq L^−1)	^133Cs (ng L^−1)	^137Cs/^133Cs (Bq ng^−1)
	Na^+	NH4^+	K^+	Mg^2+	Ca^2+
Pot A	3.43	ND^†	0.39	0.90	5.25	ND ~ 0.0028^†	14	ND ~ 0.0002
Pot B	3.54	ND^†	1.0	0.93	5.39	ND ~ 0.0028^†	14	ND ~ 0.0002
Pot C	3.42	0.064	1.0	1.0	5.44	5.6	29	0.19

^†The activity concentration of ¹³⁷Cs in tap water in Fukushima was referred from Shizuma et al. (2018). The detection limit (ND) of ¹³⁷Cs in tap water in Fukushima is 0.002 Bq L^−1. The detection limit (ND) of NH₄⁺ calculated from the calibration curve is 0.039 mg L⁻¹.

Table 4. Total dry mass, transfer factors of ¹³⁷Cs from soils to brown rice (pots A and B) and transfer parameters of ¹³⁷Cs from water to brown rice (mean ± sd, n = 3, except TF_soils-rice: mean ± sd, n = 6)

The total mass of brown rice (g, dry wt)			TFsoils–rice	CR–water–rice	MB–water–rice
Pot A	Pot B	Pot C
23.5 ± 3.5	20.0 ± 4.2	21.7 ± 3.0	0.0053 ± 0.0009	0.73 ± 0.30	0.0005 ± 0.0002

Figure 1. Activity concentrations of ¹³⁷Cs in rice components. The standard deviation (n = 3) is represented by the vertical lines. The symbols (?, ??) indicate the significant differences in the activity concentrations of ¹³⁷Cs in rice components between pots A, B, and pot C (P < 0.05).

Figure 2. Concentrations of ¹³³Cs in rice components. The standard deviation (n = 3) is represented by the vertical lines.

Figure 3. The ratios of ¹³⁷Cs/¹³³Cs in rice components. The standard deviation is represented by the vertical lines. The symbols (?, ??) indicate the significant differences in the ratios of ¹³⁷Cs/¹³³Cs in rice components between pots A, B (n = 6), and pot C (n = 3) (P < 0.05).

Figure 4. The relationship between the CR_{−water-rice} parameter and exchangeable K in soils. The K content in fertilizer was also included in the exchangeable K in our study. The triangles represent the CR_{−water-rice} parameters calculated from the data of Suzuki et al. (2015). The circle represents the CR_{−water-rice} parameter in this study.

Figure 5. The activity concentration of ¹³⁷Cs in soils collected from pot C after harvesting rice. The standard deviation (n = 3) is represented by the vertical lines. The symbols (?, ??) indicate the significant differences in the activity concentration of ¹³⁷Cs between the 0-1 cm soil layer and the underneath soil layers.

Table 5. The concentrations of ¹³⁷Cs, ¹³³Cs, and other cations in irrigation water that was collected from Minamisoma, Fukushima

Year	Cations (mg L^−1)					Dissolved ^137Cs (Bq L^−1)	^133Cs (ng L^−1)	^137Cs/^133Cs (Bq ng^−1)
	Na^+	NH4^+	K^+	Mg^2+	Ca^2+
2020	5.49	ND^†	0.62	1.17	5.75	0.032	5.17	0.00619

^†The detection limit (ND) of NH₄⁺ calculated from the calibration curve is 0.039 mg L⁻¹.

Table 6. The concentrations of ¹³⁷Cs and ¹³³Cs in soils, the exchangeable fraction of soils, and brown rice that was collected from Minamisoma, Fukushima (mean ± sd, n = 3)

	Soils	Exchangeable fraction	Brown rice
^137Cs (Bq g^−1) dry wt	1.04 ± 0.06	0.078 ± 0.004	0.0012
^133Cs (ng g^−1) dry wt	2620 ± 790	45 ± 1	0.75
^137Cs/^133Cs (Bq ng^−1)	0.000397 ± 0.000105	0.00173 ± 0.00007	0.00162

Shizuma, K., Y. Fujikawa, M. Kurihara, and Y. Sakurai. 2018. “Identification and Temporal Decrease of 137Cs and 134Cs in Groundwater in Minami-Soma City following the Accident at the Fukushima Dai-ichi Nuclear Power Plant.” Environmental Pollution 234: 1–8. doi:10.1016/j.envpol.2017.11.018.

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Suzuki, Y., T. Yasutaka, S. Fujimura, T. Yabuki, M. Sato, K. Yoshioka, and K. Inubushi. 2015. “Effect of the Concentration of Radiocesium Dissolved in Irrigation Water on the Concentration of Radiocesium in Brown Rice.” Soil Science and Plant Nutrition 61 (2): 191–199. doi:10.1080/00380768.2014.1003192.

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