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Feasibility study for using modelling rather than monitoring to refine pesticide leaching assessments - PS2249

Since 2000, the regulatory assessment of pesticide leaching to groundwater has been based on the FOCUS Groundwater Scenarios. Subsequent work identified that four of the nine scenarios are relevant to UK conditions. The regulatory endpoint for pesticide leaching is both challenging and unrealistic in the majority of situations (concentration in soil pore water at 1-m depth should not exceed 0.1 ìg/L for the parent compound and 10 ìg/L for metabolites). Recent changes to EU guidance on soil persistence will generally lead to larger concentrations of a particular active substance being simulated using the FOCUS groundwater (e.g. due to changes to assumptions on washoff). It is widely anticipated that a significant number of widely-used products will fail the FOCUS GW assessment during re-registration and that the requirement to address the concern will be large, expensive monitoring programmes to assess presence of individual active ingredients in groundwaters across Europe. This places a large financial and manpower burden on industry and also on regulators who will need to review complex monitoring protocols and review the resulting studies. This increase in regulatory burden seems unreasonable without further analysis given that pesticide concentration at 1 m below a single field is an extremely crude surrogate for concentrations in actual groundwater.
The aim of this project will be to assess the feasibility of introducing a higher-tier of modelling with a more realistic endpoint as an additional step before proceeding to groundwater monitoring. The project will couple soil and groundwater models to describe pesticide leaching to the surface of the groundwater body. Case studies will be developed based on two pilot areas in the UK overlying regionally-important Chalk or Sandstone aquifers. The case studies will account for spatial variation in soils, land use and hydrogeology as well as temporal variation in weather. Resulting simulations will be evaluated against groundwater monitoring data and the approach compared with current regulatory practice. The project will conclude with a workshop to disseminate results to a range of stakeholders.
1.Assess possibilities for alternative prediction endpoints;
2. Select pilot areas as representative of UK conditions and assess the distribution of land use and groundwater depth within those areas;
3. Generate and evaluate case study assessments for three pesticides to demonstrate effect of endpoint and environmental conditions on PECgw; and
4. Report findings to a stakeholder workshop and propose options for regulatory development.
Project Documents
• EVID4 - Final project report : PS2249 Final report   (1917k)
Time-Scale and Cost
From: 2013

To: 2013

Cost: £32,923
Contractor / Funded Organisations
University of York
Pesticide use              
Fields of Study
Pesticide Safety