Field measurements of pesticide drift and dissipation and regulatory exposure assumptions

Abstract Background The authorisation of current-use pesticides (CUPs) is based on standardised datasets that only partly reflect field conditions. Drift and dissipation are key processes determining the environmental presence of CUPs, yet field-based evidence of their fate is limited. This study aimed to provide best-case real-world drift and dissipation values after simultaneous application of one insecticide (pirimicarb) and three fungicides (bixafen, fluopyram and prothioconazole) in winter cereal fields. Application was performed under agricultural best practices, including the use of 90% drift-reducing technology and best-case weather conditions. Relative drift deposition into adjacent meadows was assessed using Petri dishes and environmental samples (bare topsoil, covered topsoil and vegetation) at distances of 1, 5 and 20 m downwind of the treated fields. Dissipation was monitored for up to 128 days. Residues were analysed via high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC–MS/MS). Dissipation was also evaluated with a model named MITAS (MIxture Toxicity of Application Spray series) and measured residues were compared with literature values. Results Under a best-case application scenario, measured relative drift deposition rates exceeded benchmark values in environmental samples (topsoils and vegetation) in some cases, but not in Petri dishes. Environmental samples additionally contained residues of pesticides not applied during the experiment, demonstrating cumulative off-field contamination from other nearby sources. Dissipation in in-field soils was faster than literature-based DT 50 . Although the investigated fields differed in soil type, no substantial differences in dissipation were observed. Dissipation in vegetation samples was in line with literature. Off-field samples showed substance-specific dissipation patterns and were often slower or not detectable. Conclusion Overall, our results indicate that off-field transport of current-use pesticides may occur even under agricultural best practice with drift reducing technology and optimal conditions. Moreover, concentration decrease in environmental samples may be influenced by additional atmospheric inputs, which can complicate the distinction between applied and background-derived CUPs. This highlights that environmental compartments integrate multiple exposure pathways, including direct drift deposition and diffuse environmental sources. Consequently, regulatory approaches may not fully capture the complexity of real-world exposure scenarios. Field-based measurements incorporating landscape-based exposure scenarios therefore remain essential to complement regulatory modelling approaches and to ensure that environmental risk assessments adequately reflect real-world exposure scenarios.