The table shows the annual mass of three agricultural pollutants (in thousands of tonnes) discharged into a freshwater river basin from 2012 to 2024:
| Year | Nitrates | Phosphates | Organophosphates |
|---|---|---|---|
| 2012 | 12.8 | 3.2 | 0.64 |
| 2015 | 11.4 | 2.8 | 0.52 |
| 2018 | 10.1 | 2.3 | 0.41 |
| 2021 | 9.2 | 1.9 | 0.33 |
| 2024 | 8.0 | 1.5 | 0.24 |
Calculate the percentage decrease in the annual mass of nitrates discharged into the river basin between 2012 and 2024. Show your working.
