By Giuliana Miglierini
The presence of residues of veterinary medicines, feed additives and pesticides in food of animal origin may pose exposure risks for human health. The topic has been historically approached under different perspectives according to the specific reference legislative framework and the respective authority involved in regulating and monitoring the products. The European Medicines Agency (EMA) and the European Food Safety Authority (EFSA) are among the main regulators involved in setting and verifying the legally binding maximum residue limits (MRLs) for chemical substances, together with the European Chemicals Agency (ECHA).
EMA and EFSA received in 2020 a mandate by the European Commission to work at the development of a harmonised approach to the assessment of dietary exposure to residues of veterinary medicines in food of animal origin. The comparison of the current situation run by the two agencies included only exposure assessment methods used in the regulatory areas, which are all based on traditional deterministic approaches. The resulting recommendations have recently been published in the form of a joint report.
EMA/EFSA experts focused on key concepts and features in order to provide a general agreement on the basic “building blocks” of a recommendable harmonised methodology, leaving the setting up of more detailed methodological aspects targeted to the different sectorial applications to a further phase of discussion. The document shall now be assessed by the European Commission and, if adopted, may request the implementation of specific action targeted to the different sectors to reach a better harmonisation. The Technical Report to be submitted to the Commission may also contain other elements to be considered.
Meanwhile, on 9 February 2023 the Commission implementing Regulation (EU) 2022/1255 designating antimicrobials or groups of antimicrobials reserved for treatment of certain infections in humans entered into force. The regulation lists a wide range of antibiotic, antiviral and antiprotozoal active substances. Those use is from now on excluded to treat animals, so to preserve their efficacy in humans. The measure is part of the broader approach against antimicrobial resistance, and it aims to promote a more prudent and responsible use of antimicrobial medicinal products in animals, including very strict rules on their veterinary prescription for prophylactic and metaphylactic use.
The main issues examined by the EMA/EFSA report
Sectorial legislations in the field of medicinal products (managed by EMA), food (EFSA) and chemicals (ECHA) may greatly differ from one another in the approach and methodologies chosen to define exposure limits and to run risk assessments referred to residues of veterinary medicinal products, feed additives, pesticides and biocides. This lack in harmonisation may lead to significantly different outcomes in the assessment of the same active substance, especially when it is characterised by a dual use for applications in different sectors.
There are several pieces of legislation in place aimed to guarantee a high level of protection of both human and animal health and the environment [Commission Regulation (EU) 2018/7829, Regulation (EC) No 1107/200910 and Commission Regulation (EC) No 429/2008], as well as sectorial legislations in the pharmaceutical, food, and feed additives fields that may diverge at the level of data requirements, purpose of the required studies, methodologies for exposure assessment, consumption models, etc.
In general terms, exposure studies are usually run using radiolabeling to trace the fate of a substance and to characterise its metabolites and their concentration in edible tissues/food commodities from target animals. The “residue of concern” (RoC) considered in the dietary exposure assessment is most commonly estimated assuming that metabolites have the same pharmacological/ toxicological potential as the parent compound. The difficulty of measuring the concentration of all compounds in residue monitoring often leads to the selection of a marker residue to be traced.
Health Based Guidance Values (HBGVs, or Reference Values) corresponds to the concentration of a chemical that may present hazards for the human, animal or environmental health; they are listed in the EFSA Open Food Tox Database, as well as in similar WHO and US-EPA databases.
HBGV, as well as acceptable daily intake (ADI) in case of chronic risk and the acute reference dose (ARfD) in case of acute risk, can be used in association with the estimated dietary exposure to the RoC to evaluate the risk of exposure.
The report initially discusses the different approaches and models currently in use by EMA, EFSA, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and the Joint Meeting on Pesticide Residues (JMPR). Reference is made to the alternative definitions for the establishment of residue limits related to veterinary medicinal products charactering the different sectorial legislation, as well as to methods to assess the related hazard.
The Theoretical Maximum Daily Intake model (TMDI, or diet-based approach), for example, is used by EMA to estimate the risk from life-long exposure to residues in food commodities from animals treated with veterinary medicinal products. This model has been already abandoned by JECFA and EFSA, that switched respectively to the Feed Additives Consumer Exposure (FACE) and Pesticide Residue Intake Model (PRIMo 4), as better suited to estimate age-dependent exposure scenarios based on individual food consumption data. The report also discusses the Global Estimated Chronic Dietary Exposure (GECDE) model, and the International Estimated Daily Intakes (IEDI) model. This last one is based on the WHO GEMS Food Cluster diets, estimating average per capita consumption figures based on international trade and production statistics of foods.
A further level of complexity in the assessment has to be considered for substances with dual uses, such as veterinary medicines and pesticides. In such instances, it is important to note that maximum residue limits/levels may vary for the same substance in the same animal commodity, as their concentration may differ in different tissues and/or organs (i.e., muscle, fat, liver, kidney, eggs, or milk). This may result in uncertainties at the level of the enforcement of the appropriate level and residue definition by different authorities.
The recommendations for future harmonization
The analysis and evaluation of the performance of the many available methods led EMA and EFSA to conclude that the observed differences in exposure assessment could be primarily attributed to the type and use of consumption and occurrence data. Other possible elements impacting on the obtained result may include the chosen calculation model and exposure model, the exposure to residues from multiple uses, and the use of commodity definitions and combined exposure from multiple species. Different timelines in the implementation of scientific innovation may have also contributed to the observed divergences.
The final goal of the exercise was to obtain a most realistic exposure assessment possible based on the available methodologies. The so identified “preferred methodology” focuses on data sources and models, includes also alternative proposals on a number of items, and it might represent the “blueprint” for a future harmonised methodology. EMA and EFSA’s recommendations pay particular attention to exposure assessment as the first step of a risk assessment; as for risk characterisation, no specific recommendations have been developed during this round of discussions.
