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Preliminary investigations for reducing uncertainties in estimates of non-target contamination by pesticide sprays - PS2025

Assessments of potential off-target exposures from spray drift, for the regulatory approval of pesticides, require the use of models. For bystander and resident exposures, the computer-based BREAM model has been recently developed. Potential exposures of surface water are determined from a combination of empirical field data and a physical model based on a wind tunnel configuration that uses a single stationary nozzle.

There are uncertainties in the use of such models, some of which arise from differences between the model system and reality which are an inevitable consequence of our incomplete understanding of reality, and some because of necessary simplifications of the real system in order to produce a practical model. It is important to quantify such uncertainties by wherever possible comparing model predictions with real data. Reductions in uncertainties will ensure that risk assessments are not unnecessarily precautionary and that valuable active ingredients can be registered.

The BREAM model, which is being considered as a regulatory tool in the UK, has a number of sources of uncertainty, some of which can be reduced by further investigations. Development of the spray drift model on which the BREAM model is based has now stopped under the existing BREAM project. There are, however, areas where the model can be improved, particularly relating to the modelling of variability using distributions of inputs and to the characterisation of the airflows around a boom of nozzles and their interaction with the wind and forward motion. Some preliminary investigations are proposed in order to enable possible approaches to improving the model to be defined.

The LERAP scheme for risk assessments for surface water has been well established for specific situations, but it is likely its use will need to be extended to wider buffer zones and unconventional methods of operating nozzles, for which the existing model and methodology may not be appropriate.

This preliminary project aims to undertake some initial studies to explore:

1. Published information that can be incorporated into improving the simulation of variability from boom height and wind speed fluctuations in the BREAM model;
2. Wind tunnel techniques for making the necessary measurements to improve our understanding of the interactions between a spray and a cross wind and therefore our model of spray behaviour close to the nozzle;
3. The comparison between the BREAM models and data from Fera that has recently become available which will contribute to quantifying model uncertainties;
4. Methods of undertaking a LERAP assessment in the wind tunnel with alternative nozzle configurations
1. Review available data and literature relating to the two areas of variability that are currently included in the BREAM model
a. Boom stability
b. Wind characteristics
2. Investigate possible techniques for determining, in the Silsoe wind tunnel, the interaction between a cross wind and a moving boom of nozzles for improving nozzle characterisation in the Silsoe Spray Drift Model
3. Compare a proposed alternative wind tunnel configuration for a LERAP test with the existing one for a nozzle where field data is available
4. Undertake an analysis of data obtained by Fera and compare with current model predictions to contribute to quantification of model uncertainty.
a. spray drift data, including tall crop
b. volatilisation data
Project Documents
• EVID4 - Final project report : PS2025 sid5 v2 Final Report   (503k)
Time-Scale and Cost
From: 2010

To: 2010

Cost: £36,170
Contractor / Funded Organisations
The Arable Group
Agricultural Land              
Environmental monitoring              
Environmental Protection              
Fields of Study
Pesticide Safety