Aged sorption in groundwater assessment for pesticide registration in Great Britain and Northern Ireland

When you are applying for pesticide registration in Great Britain and Northern Ireland you must demonstrate that use of the pesticide does not result in unacceptable risk of groundwater contamination. Guidance is available on Groundwater assessment for pesticide registration in Great Britain and Northern Ireland.

If a first-tier groundwater assessment gives an unacceptable risk assessment, the regulatory process allows you to refine the assessment. One way to refine the assessment is to use data on aged sorption of the substance. Aged sorption is a process whereby substances become more strongly adsorbed to soil over time.

In depth guidance is available at Guidance on how aged sorption studies for pesticides should be conducted, analysed and used in regulatory assessments. The guidance is currently in a draft stage and holds no official status in pesticide regulatory procedures in Great Britain/Northern Ireland or Europe at the time of writing. Until the guidance is officially noted, it is strongly advised that you contact HSE to discuss its use beforehand.

Using aged sorption parameters in pesticide leaching assessments

Aged sorption (or time dependent sorption) is a natural environmental process by which substances can become more strongly adsorbed to soil over time. This can result in reduced leaching to groundwater. First tier FOCUS groundwater modelling does not take aged sorption into account, but the models do have the capability to take this process into account at higher tiers. The data requirements in Regulation (EC) 283/2013 do not specifically require applicants to generate aged sorption data. However, with relatively simple modifications to standard soil degradation studies you can generate data on aged sorption to use in higher tier FOCUS groundwater modelling. Guidance on how to generate and use aged sorption data in FOCUS groundwater models can be found in the document Guidance on how aged sorption studies for pesticides should be conducted, analysed and used in regulatory assessments.

Generating the experimental data does not guarantee being able to produce robust aged sorption information. In addition, new data does not always result in reducing predicted concentrations sufficiently to pass the risk assessment. You must be aware of this before undertaking such additional work.

At the time of writing, the guidance is in a draft stage and holds no official status in pesticides regulatory procedures in the GB/NI or Europe. Until the guidance is officially noted, it is strongly advised that you contact HSE to discuss its use beforehand.

Background to the aged sorption guidance

Two initial research and development projects funded by Defra investigated aged sorption of pesticide substances (reports available for PS2206 and PS2228). These projects led to the development of an initial draft guidance document on how aged sorption studies for pesticides should be conducted, analysed and used in regulatory assessments under Defra funded project PS2235. The guidance document developed is available by contacting HSE.

A workshop was subsequently held in 2010 to assess the proposed new guidance document. The proceedings of this workshop and associated can be made available by contacting HSE. The guidance was amended to incorporate the recommendations from the workshop and new information from an additional Defra funded project (PS2244, and associated annex and technical report). The guidance was submitted to be assessed by the Panel on Plant Protection Products and their Residues (PPR) of the European Food Safety Authority (EFSA). Further investigations on generating aged sorption information for metabolites and field dissipation studies were conducted under Defra funded project PS2254 (and associated technical reports on field data and metabolites). The PPR issued an initial statement (Statement on the FERA guidance proposal: 'Guidance on how aged sorption studies for pesticides should be conducted, analysed and used in regulatory assessments' (FERA, 2012)) which resulted in a revision of the draft guidance. The revised guidance was the subject of a definitive PPR opinion (Scientific Opinion about the Guidance of the Chemical Regulation Directorate (UK) on how aged sorption studies for pesticides should be conducted, analysed and used in regulatory assessments). The current guidance is the result of a further revision to take the PPR opinion into account.

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Updated 2021-08-10