National differences in drift reduction classification of plant protection technologies in Europe: implications for...

Spray drift is a key pathway for pesticide entry into non-target compartments such as surface waters and semi-natural habitats. Across Europe, national schemes use different reference nozzles and operating parameters to assess drift reduction. We provide a head-to-head, standardised comparison of national reference systems in the wind-tunnel to quantify how reference selection and parameterisation shape the drift potential (DP) of identical nozzles. Using national reference parameterisations (e.g., pressure, driving speed, boom height) in a single wind-tunnel, we measured DP with three technical repeats per setting and report DP as mean with replicate range [min-max]. Reference definitions and operating parameters produced order-of-magnitude shifts in DP: for the same nozzle (TeeJet TP 11003-SS), DP ranged from 55 (NL) to 717 (EFSA) (≈13× difference); a 0.7 km h^-1 speed change (DE vs. NL) halved DP. We did not assign DR classes from tunnel data because uniform DIX thresholds are not available for all references. Instead, we show that the DP sensitivity observed under identical conditions explains the cross-country DR discrepancies documented in national listings. Divergent reference systems - not intrinsic nozzle performance - drive much of the variation in measured drift potential and thereby explain practical differences in listed DR classes across countries. We outline elements for EU-wide harmonisation: standardised field protocols, conversion factors between methods, a common reference set (nozzles/parameterisations), and transparent publication formats to improve comparability, regulatory consistency, and environmental protection.