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Correlations of fluoride levels in acid insoluble substances with those in soils and non-carbonates.
| Correlation coefficient | Surface soil | Soil in the mineral horizon | Farmland soil | Non-carbonates |
|---|---|---|---|---|
| r | 0.7120** | 0.8899** | 0.7264** | 0.9421** |
**Indicate correlation at P < 0.01.
