| Sources | Concentration |
| Ultramafic igneous rock | 1800 mg kg−1 |
| Basaltic igneous rock | 200 mg kg−1 |
| Shales and clays | 120 mg kg−1 |
| Black shales | 100 mg kg−1 |
| Sandstone | 35 mg kg−1 |
| Granitic igneous rock | 20 mg kg−1 |
| Limestone | 10 mg kg−1 |
| Fresh water | 0.1 - 117 mg L−1 |
| Sea water | 0.2 - 50 mg L−1 |
| Earth crust | 0.1 - 0.3 mg kg−1 |
| Air (urban) | 0.015 - 0.03 mg m−3 |
| Air (rural) | 59 × 10−6 mg m−3 |