Harmonizing maximum residue limits for pesticides in animal-derived foods

Many regulatory agencies establish maximum residue levels (MRLs) for pesticides in livestock products to protect human health. However, the relationships between pesticide MRLs across different products from the same livestock animal and their impact on animal health remain unknown. To address these questions, we developed compatibility, livestock-health, and human-health mechanisms within a regulation-oriented framework. For the compatibility mechanism, which aims to prevent inconsistencies in the MRLs of pesticides set for raw livestock products, we simulated uncertainty intervals for the suggested MRL ratios in raw products from cattle and sheep. For the livestock and human-health mechanisms, we introduced pesticide-specific elimination-equivalent (PSEE) exposure slopes to evaluate animal exposure risks, based on the legal limits of pesticides. Simulation results find that the median suggested MRL ratio of bovine meat (with ~ 20% fat content) to liver (with ~ 3.6% fat content) was 4.90, while the median ratio of liver to kidney was 1.18, indicating that the ratios were determined by the log KOW of the pesticides and the fat content of livestock products. The compatible intervals for DDT's suggested MRL ratios were [3.80, 6.42] for meat/liver and [4.51, 7.62] for meat/kidney. The calculated PSEE exposure slopes reveal that, in general, lipophobic pesticides have steeper PSEE exposure slopes, meaning higher exposure is required to reach the default residue level. For example, assuming a reservation coefficient (ζ) of 1.0, the PSEE exposure slopes of oxamyl (log KOW = − 0.47) are 0.12 and 0.16 kg kg⁻1d⁻1 for bovine milk and liver, respectively, while DDT (log KOW = 6.91) shows values of 0.066 and 0.064 kg kg⁻1d⁻1. These findings provide a new perspective for improving the comprehensive regulatory process.