Refining the non-dietary risk assessment by using half-lives (DT50) from magnitude of residue studies as a surrogate to dislodgeable foliar residue (DFR) decline

This study addresses the refinement of non-dietary risk assessments for plant protection products (PPPs) by evaluating the use of total residue (TR) half-lives (DT50) from magnitude of residue (MOR) studies as surrogates for dislodgeable foliar residue (DFR) decline, which is critical for estimating worker, resident, and bystander dermal exposure. While DFR field studies are not routinely conducted for every PPP, supervised MOR field trials to determine TR are standard regulatory requirements worldwide. To assess the viability of using TR decline rates for DFR decline in risk assessment models, we analyzed a comprehensive dataset comprising 71 DFR and 275 MOR GLP-compliant paired trials across various crops. Statistical analysis revealed that DFR residues dissipate, on average, three times faster than total residues from MOR studies, with the 95th percentile indicating a 2- to 4-fold faster decline. These findings suggest that, in the absence of DFR field data, TR decline rates provide a conservative and protective surrogate for modeling DFR decline and refining non-dietary risk assessments. This approach could also inform the design and duration of future DFR studies, potentially reducing the need for extended GLP-complaint DFR field trials without compromising regulatory rigor or worker safety.