The European Food Safety Authority (EFSA) has lowered the toxicological reference value for phosphonic acid as part of its current peer review of the active substance choline hydrogen phosphonate. An initial assessment indicates that the current maximum residue levels (MRLs) may lead to exceedances of the new acceptable daily intake (ADI) for certain consumer groups. EFSA therefore recommends reviewing the existing MRLs for phosphonic acid and its salts.
Choline hydrogen phosphonate is a new active substance for which approval for use in plant protection products has been applied for. As the substance is a salt of phosphonic acid, phosphonic acid was a key focus of the toxicological assessment.
Based on a developmental toxicity study in rabbits, EFSA derived an ADI of 0.69 mg/kg body weight (bw) per day, thereby replacing the previous EFSA ADI of 1 mg/kg bw per day established in 2018. Furthermore, EFSA still considers the derivation of an acute reference dose (ARfD) unnecessary (EFSA Journal. 2026;24:e10288).
The potential implications for the existing MRLs are particularly relevant with regard to the residue definition “phosphonic acid and its salts, expressed as phosphonic acid”. Since the ADI was lowered, EFSA updated the chronic exposure by using the new ADI. This screening exercise showed exceedances of the new ADI for certain consumer groups. Therefore, EFSA recommends a revision of the assessment of existing MRLs for phosphonic acid.
However, any changes to the current MRLs will take time. First, the new ADI needs to be formally endorsed at EU level. This may then be followed by a review of the existing MRLs, whereas any amendment of Regulation (EC) No 396/2005 would come at a later stage. It is therefore likely to take several years before revised MRLs apply.
