Risk assessment for birds and mammals: Seed dissipation residue trials

Wildlife may potentially be exposed to plant protection products on treated seeds.

One assumption of the Tier 1 EFSA long-term bird and mammal risk assessment is that residues of pesticides on treated seeds do not decline over time after they are sown in the field. Therefore, a worst case time-weighted average factor (fTWA) of 1 (i.e., no dissipation) is used to calculate residue concentrations on seeds for the chronic risk assessments. This worst case assumption is still present in the updated EFSA (2023) Guidance on the risk assessment for Birds and Mammals (EFSA Journal, 21(2) 7790).

However, based on a large residue dataset and supporting literature data, the default foliar DT50 value of 10 days equating to a 21-day fTWA value of 0.53 is used for foliar degradation following spray applications. This means that seed treatment chronic bird and mammal risk assessments are inherently more conservative and unrealistic compared to those for spray applications.

Seed dissipation residue trials may provide data that can refine the default fTWA value of 1 to values less than 1 for treated seeds.

To support refinement of the EFSA bird and mammal treated seed risk assessment, Staphyt can conduct field dissipation trials within its European GLP field stations network in Northern and Southern EU zones (France, Spain, Italy, Greece, Poland, Hungary, Germany and Austria). Treated seeds are sown or scattered on bare soil, covered with a net for protection, then sampled for residue analysis at various intervals. Residue decline of the active substance(s) present on the seed can then be determined from the analytical measurements made at each sampling time point.

If you want to read more about the EFSA Guidance Document (GD) ‘Risk assessment for birds and mammals’, please read what our experts has to say in this news on our website.