Assessment of Current Guidance and Potential Improvements for Aged Sorption Studies

August 23, 2016

A few years ago, a guidance proposal on how to conduct aged sorption studies for pesticides was published (FERA, 2012).  Since then several registrants have performed studies following the recommendations in this guidance.  However, last year the European Food Safety Authority (EFSA) scientific Panel on Plant Protection Products and their Residues (PPR) issued a statement (instead of a scientific opinion) on the FERA guidance proposal and concluded that they could not recommend the use of the guidance for the time being.  They expressed concerns about the interpretation of the experiments and how the results of these experiments should be used in the regulatory leaching models.  While they generally agreed with most of the recommendations in the FERA guidance, the PPR also saw what they felt were ways the guidance could be improved upon and provided a set of conclusions and additional recommendations designed to do so. Through investigating possible options for improvement, the PPR was unable to complete its evaluation due to non-availability of relevant data needed to test these options.

The PPR recommended that the current FERA draft guidance document be updated, taking into account the conclusions and recommendations for improvement provided in their statement.  In, a recent update provided by EFSA (18th International Fresenius AGRO Conference, June 2016), it was reiterated that the PPR scientific opinion will be prepared when the FERA draft guidance document has been updated.

The two major recommendations are related to the optimization procedure as summarized below:

  1. The panel was not in agreement with the guidance recommendation on the minimum sampling time points to be included in the fitting procedure.  More specifically, the panel disagreed with the idea of excluding earlier sampling points by default in order to obtain a better fit.  Their recommendation is to always check whether or not the PEARLNEQ model is capable of describing the entire period of the experiment adequately.  If the model fails, then a stepwise approach may then be taken, excluding certain points in a second step.  In order to perform a thorough evaluation of this approach, original data from aged sorption experiments should be submitted.
  2. The Panel recommends always performing an initial check as to whether or not the fitted model is capable of adequately describing the measured data without excluding any time points and fixing KOM, EQ to that measured at day 0 of the time-dependent sorption experiment. Original data from aged sorption experiments were requested by the panel in order to test this recommendation.


Once the draft guidance is updated to address these two recommendations, along with all the other suggestions, an EFSA scientific opinion will then be issued. 


FERA (Food and Environment Research Agency), 2012. Guidance on how aged sorption studies for pesticides should be conducted, analysed and used in regulatory assessments. The Food and environment Research Agency, Sand Hutton, York, UK.

To discuss these and other testing strategies in detail, contact:

Dr. Kalumbu Malekani  
+1 508-295-2550

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