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A Statistical Approach to Estimating Soil-to-Plant Transfer Factor of Strontium in Agricultural Fields

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This study, published in Japanese with English abstract and tables, measured stable strontium in soils and the edible parts of crops from 142 Japanese farm fields as a stand-in for radioactive strontium-90. Crop calcium was the strongest predictor of how much strontium a crop took up from soil, and a two-variable regression on soil strontium and crop calcium predicted transfer factors well.

Key numbers

  • Soil strontium: geometric mean 78 mg/kg, range 12 to 360 mg/kg (n = 142) (Table 1, p. 2).
  • Crop strontium (edible parts): geometric mean 1.6 mg/kg dry weight, range 0.13 to 88 mg/kg dry weight (n = 146) (Table 2, p. 2).
  • Geometric mean dry-weight transfer factors: brown rice 0.0032 (n = 61), wheat 0.014, potato 0.020, soybean 0.077, tomato 0.048, cabbage 0.17, spinach 0.27, Chinese cabbage 0.50 (Table 3, p. 3).
  • Crop calcium correlated strongly with the transfer factor (rank correlation 0.88) and with crop strontium (0.91); soil strontium and crop strontium were not correlated (p above 0.05) (Results, pp. 2 to 4; Fig. 1).
  • Regression: log TF = -0.88 log(soil strontium) + 0.93 log(crop calcium) - 2.53, adjusted R squared 0.91 (Results, p. 4).

Methods (brief)

Soils (0 to 20 cm) and edible crop parts were sampled at harvest from 142 fields; soil properties and element concentrations in soils and crops were measured as described in an earlier institute report. Spearman correlation, stepwise selection and multiple linear regression were used; crop calcium from the Japanese food composition table was substituted to predict transfer factors without measuring crops.

Evidence fitness

Supports background stable strontium levels in Japanese agricultural soils and crops, crop-specific soil-to-crop transfer factors, and the controlling role of crop calcium. Stable strontium is used as an analogue for strontium-90; the paper does not measure radiostrontium, intake or health effects.

Limitations

Analytical methods and detection limits are described in a separate report not archived here. Several crops have only one or two samples. Crop concentrations are on a dry-weight basis, which limits direct comparison with fresh-food data. The work was funded by a national radioactive-waste research budget.

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