Tasmanian River Catchment Water Quality Initiative

Final Report
Department of Environment, Water, Heritage and the Arts, January 2009
ISBN 978 0 642 55482 6



The Tasmanian River Catchment Water Quality Initiative aimed to improve understanding of the pesticides used in Tasmania, the fate of pesticides in the Tasmanian environment and the risk of waterway contamination by pesticides.

A major component of the initiative was adapting the Pesticide Impact Rating Index (PIRI) to Tasmanian environmental conditions. PIRI is a risk indicator developed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) that helps the user evaluate the potential risk that a pesticide will move away from the area where it was applied and into surface or groundwater. PIRI assists with decision making, so that pesticide users can select the most appropriate pesticide or the best time for pesticide application.

Each component of the initiative was carried out by a different organisation:

  • The Department of Primary Industries and Water (DPIW) determined the nature and extent of agricultural and forestry pesticide use in Tasmanian river catchments.
  • The Tasmanian Institute of Agricultural Research (TIAR) studied the half-life (days required for a pesticide to decrease in the soil by half of its initial amount) and sorption (how the pesticide molecules bind to the different soil types) of selected pesticides and soils in Tasmania.
  • Forestry Tasmania gathered historical water quality monitoring data and corresponding site and climate data.
  • CSIRO used the information from the previous three projects to adapt PIRI to Tasmanian conditions and compare the predictions of the new tool, PIRI-Tas, against the historical monitoring data.

The DPIW project compared two methods for estimating the nature and extent of pesticide use in Tasmania’s river catchments. The grower survey method best informed conclusions on pesticide use in Tasmania, and DPIW identified ways to further improve this method for more reliable estimates. Nine pesticides were added to PIRI-Tas as a result of this project.

The TIAR project demonstrated that the sorption and half-life values for pesticides in Tasmanian soils were different to those found in previous studies in other locations. This highlights the importance of including local data in risk-assessment tools like PIRI. The project also clarified some processes that affect the environmental fate of pesticides, including the important role of soil pH for some pesticides.

Forestry Tasmania collated existing data on water quality, site conditions and climate. These data were used to validate and refine PIRI for use in Tasmania. Forestry Tasmania found that buffer zones were effective in reducing the risk of contamination after a spray operation, and that most contamination occurred when drainage lines were sprayed or buffer zones were not vegetated.

Through this project, CSIRO has substantially improved PIRI to make it more suitable for use in Tasmanian conditions. Although appropriate data for validating a model like PIRI are difficult to obtain, the available data demonstrated that PIRI-Tas was effective at estimating the risk of waterway contamination by pesticides under different conditions.

PIRI-Tas offers a major advance from the previous version, and has set the foundation for further improving the usefulness of PIRI for pesticide risk reduction in Australia and overseas. Although PIRI-Tas does have limitations and requires further validation, the science behind its development and testing provide a basis for use with reasonable confidence. It offers an advance over alternative methods of assessing the likelihood of pesticides migrating into waterways.