| Value | Category | Cases | |
|---|---|---|---|
| 1 | Air | 9 |
30%
|
| 2 | Soil | 3 |
10%
|
| 3 | Water | 2 |
6.7%
|
| 4 | Don't know | 16 |
53.3%
|
| Sysmiss | 532 |