GRG Position on Grass Residue Decline Data for Chronic Wild Mammal Risk Assessment
In the 2021 dRAR for glyphosate, the RMS requested that the grass residue decline data, used to refine the level of residues anticipated on dietary items for the chronic wild mammal risk assessment, may need to be re-assessed using current kinetics analysis approaches.
In the chronic mammal risk assessment, a refined residue decline DT50 value of 2.8 days is used to replace a default DT50 value of 10 days that is used in the calculation of a time weighted average value (fTWA) and applied in the chronic risk assessment, principally for the small herbivorous mammal (common vole -Microtus arvalis).
The GRG performed a kinetics re-analysis of the data from 22 sets of grass residue trials on which the mean DT50 value of 2.8 days is based as presented in the EFSA (2015) conclusion on glyphosate.
This historical data set comprises 18 non-GLP and 4 GLP sets of data. The non-GLP trials were conducted before GLPs were implemented. The re-analysis of the residue decline data was conducted according to the kinetics analysis requirements highlighted by the RMS in the 2021 dRAR. The GRG have concluded that there are sufficient robust data that provide a strong weight of evidence, to support the use of a DT50 of 2.8 days to refine the chronic wild mammal risk assessment. All 22 trials are considered to support a DT50 < 10 days. The four GLP trials were considered the most reliable for DT50 determination, with a worst maximum DT50 value of 2.6 days and a range of DT50 values of between 0.41 to 2.6 days.
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