Situation in Austria
For the control of domestic foodstuffs for nitrofurans, there is a testing program within the framework of the National Residue Control Plan (NRKP) in the sense of preventive consumer protection, which comprises approx. 230 samples per year (animal tissues, milk, eggs, honey and animal feed).
Furthermore, samples are examined within the scope of actions of the official food control as well as in case of suspicion. Special attention is paid to the control of products from countries outside the EU (e.g. shrimps and prawns from the Southeast Asian region).
Residues of nitrofurans in food
By splitting off the nitrofuran group in the molecule, nitrofurans are rapidly metabolized in the organism:
A large part of the released side chains binds covalently to proteins of the tissue and is degraded only slowly, e.g. in muscle and liver. Therefore, not the parent substances but the metabolites are analyzed in order to be able to detect misuse of nitrofurans for as long as possible.
In order to ensure a uniform approach with regard to the performance of the analysis and the interpretation of the results within the EU, an RPA (reference point for action) of 1 µg/kg has been set for nitrofuran metabolites (Commission Regulation (EU) 2019/1871; the RPA will be reduced to 0.5 µg/kg from 28.11.2022). This means that, firstly, the detection limits of the laboratories must be below the RPA and, secondly, results above the RPA must be judged as positive ("non-compliant"). Foods with nitrofuran metabolites below the RPA are marketable, but the cause of the residues is being investigated.
If semicarbazide is found in foods of animal origin, caution should be used in interpreting the result. This relatively simple compound does not have to come from an illegal application of nitrofurazone; there are other sources:
- Migration from plastic packaging into food, for example, azodicarbonamide, which can react to a small percentage to form semicarbazide, was used to make foamed plastic gaskets in metal lids. Its use has been banned since August 2005.
- Semicarbazide can occur naturally in shrimp.
- In some non-EU countries, azodicarbonamide may be used as an oxidizing agent in flour treatment; for example, contamination of meat from breading may occur.
- Semicarbazide may be formed during the production of egg powder.
- Semicarbazide can be carried into honey by bees from certain flowers.
In the Department of Veterinary Medicines, Hormones and Contaminants of the Institute of Food Safety Vienna we analyze nitrofuran metabolites and nitrofuran parent substances in diverse sample types and are also the National Reference Laboratory for these investigations.
- Liver (due to the higher concentration and thus better detectability of nitrofuran metabolites in liver than in muscle, liver samples from slaughtered animals are examined within the framework of the NRKP )
- Aquaculture (shrimps, prawns, fish)
- Eggs and egg preparations
- Baby food and other food samples
- animal feed (since no metabolization takes place here, the nitrofurans are analyzed as such)
Method of analysis
In animal matrices, the nitrofuran metabolites are released by mild acid hydrolysis and derivatized with nitrobenzaldehyde. After purification with ethyl acetate, the derivatives are measured by LC-MSMS. According to Commission Implementing Regulation (EU) 2021/808, a mass spectrometric method is required for the confirmation of banned substances.
The detection limits are at or below 0.1 µg/kg.
Commission Regulation (EU) No. 37/2010 of 22 December 2009 on pharmacologically active substances and their classification with regard to maximum residue limits in food of animal origin (OJ EU No. L 15, 20.1.2010).
Commission Implementing Regulation (EU) 2021/808 of 22 March 2021 concerning performance criteria for methods of analysis for residues of pharmacologically active substances in food-producing animals and the interpretation of results and methods to be used for sampling and repealing Decisions 2002/657/EC and 98/179/EC.
Last updated: 20.12.2021