First-tier regulatory risk assessments for pesticides assume that pesticide sorption is instantaneous and fully reversible. In Europe, a change in sorption over time (aged sorption) is increasingly considered at the higher tier to revise predicted environmental concentrations in groundwater. To address a need in regulatory guidance in this area, the UK Chemicals Regulation Directorate (CRD) commissioned research that formed the basis of a guidance document. The guidance proposes (i) protocols on how to measure aged sorption, (ii) procedures to fit kinetic models to the experimental data, (iii) criteria to test the reliability of the model parameters, and (iv) procedures for use of the parameters in the groundwater exposure assessment. The draft guidance was presented to and discussed with European stakeholders at a workshop. The participants were positive about this initiative and agreed that the proposed principles should be applied to real datasets to gain more practical experience. Members companies of the European Crop Protection Association (ECPA) provided datasets and funding for testing of the guidance against 127 studies by an independent organisation (Battelle UK Ltd). The results were peer reviewed by Fera. Comments from the workshop and the results of the evaluation and peer review were incorporated into a revised guidance. This document is now under consideration for further development at EU level. The evaluation of aged sorption studies, estimation of model parameters, and their incorporation into regulatory assessments is detailed and complex. The current guidance applies to laboratory studies with directly dosed substances. Further UK Defra funded research is ongoing to investigate the estimation of aged sorption parameters for metabolites formed from dosed parent substances and for substances in field dissipation studies. The guidance document will be summarised and first results of the ongoing research will be presented.

Guidance on how aged sorption studies for pesticides should be conducted, analysed, and used in regulatory assessments

246th National Meeting (2013)

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