The European Food Safety Authority (EFSA) has derived crop-specific conversion factors for setting maximum residue levels (MRLs) of the fungicide prothioconazole, concluding that existing EU uses will not pose a risk to consumers' health. In a reasoned opinion published on 8 July 2026, EFSA assessed data submitted by Bayer AG Crop Science Division to address data gaps from the MRL review, confirming tentative MRLs for leek, Brussels sprouts, barley, oat, wheat, rye grain and animal commodities, while revising conversion factors for root crops and oilseeds. The findings are provisional pending the European Commission's decision on the renewal of prothioconazole approval.
The application, submitted under Article 6 of Regulation (EC) No 396/2005, did not propose changes to existing EU MRLs set in Regulation (EU) 2024/1318 but sought to confirm the margin of safety of conversion factors. The dossier was submitted to EFSA on 3 January 2023, declared admissible by France on 24 May 2023, and followed by a public consultation from 20 July to 10 August 2023. The French evaluation report was submitted to the European Commission and EFSA on 30 April 2025, and the Commission mandated EFSA to assess the application on 20 June 2025. EFSA performed the assessment as a follow-up of the Article 12 MRL review, focusing on crops with tentative MRLs and addressing confirmatory data gaps.
EFSA derived conversion factors for 18 crop groups, including a factor of 1 for beetroot, carrots, wheat grain, and Brussels sprouts; 2 for barley and oat grain; 2 for oilseed rape and soybeans; and 4.9 for wheat and rye straw. For onions, shallots, flowering brassica, head cabbage and dry pulses, data were insufficient to confirm tentative MRLs or derive reliable conversion factors. The updated livestock dietary burden indicates that lower EU MRLs would be sufficient in liver, kidney and edible offal of ruminants, swine and poultry, and in fat of ruminants and swine. The assessment used the existing residue definitions for enforcement and risk assessment, though EFSA noted that a broader risk assessment residue definition was proposed during the renewal process, pending data on genotoxic potential of certain metabolites.
The opinion impacts several stakeholders. For Bayer and other pesticide manufacturers, the confirmed conversion factors provide regulatory clarity for MRL compliance, though the provisional nature pending the renewal decision introduces uncertainty. EU farmers benefit from continued use of prothioconazole under existing MRLs, but may face future adjustments if the renewal leads to stricter limits. National authorities gain updated tools for MRL enforcement, but must manage the transition if conversion factors change after renewal. Consumers are reassured of no health risk from current uses, though the unresolved genotoxicity data on metabolites M15 and M17 could prompt future restrictions. The European Commission will decide on the renewal of prothioconazole approval, which may require revisiting these conclusions.