Defra - Department for Environment, Food and Rural Affairs.

Science Search

Science and Research Projects

Return to Science Search homepage   Return to Project List

Characterisation and Modelling of Time-dependent sorption of pesticides - PS2228

Description
A large number of studies have shown that the sorption of pesticides in soils increases with time, thereby reducing the availability of a compound to move to surface water and groundwater. The inclusion of time-dependent sorption in pesticide fate models would significantly improve the accuracy of environmental risk assesments for pesticides. However, the mechanisms controlling kinetic sorption are not fully understood and it is not clear which mathematical description gives the best reflection of the underlying processes. There is a need for (i) comprehensive evaluation of alternative descriptions to allow recommendation of the most robust, and (ii) development of guidance on how to select parameters for input to pesticide fate models.

The aim of the project is to deliver knowledge on the factors controlling time-dependent sorption and to propose a robust approach to incorporate descriptions of time-dependent sorption into pesticide fate models. This will be achieved by exploiting existing sources of data including the dataset generated within PS2206. The work divides into four components:

[1] Data on time-dependent sorption will be collated and analysed. The extent and rate of time-dependent sorption will be compared for various pesticides and soils. Attempts will be made to identify the main controlling factors.

[2] The next phase of the project will involve mathematical modelling. A number of alternative mathematical descriptions of time-dependent sorption will be evaluated against the experimental datasets. The model that gives the most robust description of time-dependent sorption will be recommended for implementation into pesticide fate models. Attempts will be made to identify relationships between the model parameters and soil and/or pesticide properties.

[3] Based on the results from [1] and [2], guidance will be developed on the experimental design and modelling approach to derive parameters for new compounds. If possible, default approaches to generate parameters from basic soil and pesticide properties will be proposed.

[4] New data on time-dependent sorption for selected pesticides and soils will be generated. The proposed guidance will be evaluated against the new dataset and refined if necessary.

The project will provide valuable information on the controlling factors and best descriptions of time-dependent sorption and develop guidance on how to generate input parameters. The output will underpin a UK position on whether and how to consider time-dependent sorption in regulatory assessments. The work relates to Defra research objectives: “to develop techniques to model the movement of pesticides in soils and water`; and `to ensure the underlying scientific basis for regulatory decision making is sound thereby ensuring PSD is able to form well-grounded policies and to contribute to EU and international discussion on the basis of sound scientific advice`.
Objective
The overall aim of the proposed research is to deliver knowledge on the factors controlling time-dependent sorption and to propose a robust approach to incorporate descriptions of time-dependent sorption into pesticide fate models.
The specific objectives are:
1. To use existing data to identify the main controls on time-dependent sorption;
2. To identify the most appropriate mathematical description of time-dependent sorption;
3. To develop generic guidance on how to generate parameters to give a robust description of time-dependent sorption;
4. To generate new experimental data to independently test the guidance.

Project Documents
• Final Report : Characterisation and Modelling of Time-Dependent Sorption of Pesticides   (380k)
Time-Scale and Cost
From: 2007

To: 2008

Cost: £59,150
Contractor / Funded Organisations
Central Science Laboratory
Keywords
Agricultural Land              
Environmental Impacts              
Environmental Protection              
Land              
Modelling              
Pesticides              
Risk assessment and management              
Soil              
Soils              
Fields of Study
Pesticide Safety