Australia refines run-off assessments for pesticides in dryland cropping regions

The Australian Pesticides and Veterinary Medicines Authority (APVMA) is going to set out a framework and methodology for refining aquatic exposure assessment for application in environmental risk assessments of pesticides undertaken for the APVMA. The approach is designed to move away from the current default-based deterministic assessment method to a more evidence based approach through use of long-term river (stream flow) and rainfall data.
 

The current methodology used for environmental risk assessments of pesticides utilises a deterministic approach which does not take into account temporal and spatial variables that occur in the real-world environment in which pesticides are used.
 

Publicly-available Australian environmental datasets can be used to conduct regulatory environmental risk assessments which better reflect actual environmental conditions. Such an approach has now been developed for assessing pesticide runoff risk to waterways using real world-data sets for stream flow in dryland cropping regions of Australia.
 

For assessing run-off risk, this new framework proposes several steps. The first step still relies on a standard default receiving water body, as is applied in current assessments. The second step considers the probability of rainfall events that may result in an unacceptable risk in the standard water body (as used in the current deterministic method), with a particular focus on chemical persistence. This allows identification of regions where a run-off risk assessment is best focused, and identification of those regions where based on the probability of rainfall, a run-off risk is unlikely. The third (and final) step involves the in-stream assessment through application of the long-term rainfall and stream flow data.
 

This final step applies several conservative assumptions to ensure adequate environmental protection is maintained.  These assumptions include:-
 

a) Application of the pesticide to 20% of the catchment area

b) The full treated area contributes to run-off

c) Daily rainfall is assumed to fall over a period of one hour.
 

To develop the flow data for streams in dryland cropping regions of Australia, long-term daily data from between 570 and 580 stream monitoring stations in Queensland, New South Wales, Victoria and Western Australia were assessed.  Cumulative frequency distributions for receiving water concentrations resulting from run-off were developed from these data, allowing more quantitative assessments of exposure, and hence risk.
 

Several case studies are included in the paper to demonstrate the application of the data libraries and the run-off risk assessment framework.
 

Depending on the outcomes of this pilot project which focuses on the development of the method for dryland cropping regions of Australia, the APVMA may investigate options for extending the method to other agricultural areas where tropical/sub-tropical, temperate horticultural and forestry plantations are grown.