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 |