A student investigated the impact of a sewage treatment works on a nearby river. They measured the phosphate concentration at five different sampling sites downstream from the outlet.
Table 1
| Sampling site | Phosphate concentration (mg/dm³) |
|---|---|
| Site 1 | 8.4 |
| Site 2 | 5.2 |
| Site 3 | 3.1 |
| Site 4 | 1.4 |
| Site 5 | 0.3 |
State how the phosphate concentration changes from Site 1 to Site 5.
