Sampling sites | World average shale | Lowest concentration in the present study | |
1 | 0.89 | 2.45 | |
2 | 1.78 | 4.92 | |
3 | 1.45 | 4.01 | |
4 | 0.49 | 1.35 | |
5 | 1.58 | 4.35 | |
6 | 0.85 | 2.34 | |