| Summary: | Paddy soils in some areas of southern China are contaminated by arsenic (As) and cadmium (Cd), threatening human health via the consumption of As- and/or Cd-tainted rice. To date, a quantitative understanding of how soil characteristics control As and Cd accumulation in rice grains under field conditions is still deficient. Based on 31 paired soil-grain samples collected in southern China, we statistically explored which soil parameter or parameter combination from various soil analyses best estimates As and Cd in rice. We found that CaCl<sub>2</sub> extraction of field-moist soil collected at rice harvest provided the best estimation (R<sup>2</sup><sub>adj</sub> = 0.47–0.60) for grain Cd followed by dry soil CaCl<sub>2</sub> extraction (R<sup>2</sup><sub>adj</sub> = 0.38–0.49), where CaCl<sub>2</sub> extractable Cd from moist or dry soil was the dominant soil parameter. Compared to soil totals, parameters from neither dry soil ascorbate-citrate extraction nor anoxic soil incubation improved model performance for grain As (R<sup>2</sup><sub>adj</sub> ≤ 0.44), despite their closer relevance to soil redox conditions during plant As uptake. A key role of soil-available sulfur in controlling grain As was suggested by our models. Our approach and results may help develop potential soil amendment strategies for decreasing As and/or Cd accumulation from soils.
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