Due to their carcinogenic effect, nitrofurans were included in Annex IV (list of pharmacologically active substances for which no maximum limits can be fixed) of Council Regulation (EEC) No 2377/90 in the EU more than 15 years ago. The use of nitrofurans in food-producing animals is therefore prohibited. At the start of 2010 this prohibition was superceded by Regulation (EU) No 37/2010 (Table 2), which repeals the annexes of the above-mentioned regulation.
Nitrofurans are metabolised quickly in the organism by splitting the nitrofuran group in the molecule:
Parent substance Metabolite
Nitrofurazone (Nitrofural) Semicarbazide
A large proportion of the side chains released result in covalent bonding to proteins in tissue and is only broken down very slowly, e.g. in muscle and liver. Therefore the parent substances are not analysed but the metabolites in order to be able to detect improper use of nitrofurans over the longest possible time.
For the purpose of safeguarding health - in order to guarantee sufficiently sensitive analyses - an MRPL (minimum required performance limit) of 1 µg/kg was set for nitrofurans metabolites (Commission Decision 2003/181/EC). This limit is a minimum performance limit and not a limit value, i.e. the analytical methods applied must be able to detect at least 1 µg/kg. Results lower than 1 µg/kg are, as long as they are backed up by a confirmation method, also rated as positive.
If semicarbazide is found in foodstuffs of animal origin, then caution is required in the interpretation of the results. This relatively simple compound may not necessarily originate from illegal use of nitrofurazone, as there are other sources:
- Migration from synthetic packaging into foodstuffs, e.g. azodicarbonamide, which can react to a low percentage to produce semicarbazide, was used to make foamed synthetic seals in metal lids. Its use has been banned since August 2005.
- In some non-EU states, the use of azodicarbonamide as an oxidising agent in flour treatment is permitted; thus it is possible for instance that meat becomes contaminated from a breadcrumb coating.
- Semicarbazide may be formed during the production of egg powder.
In the interests of preventative consumer protection within the scope of the National Residue Control Plan (NRKP), there is a comprehensive testing plan for monitoring domestic foodstuffs for nitrofuran metabolites.
Furthermore, samples are examined within the scope of official foodstuff-monitoring activity and in cases of suspected contamination. Special attention is given to monitoring products from countries outside the EU (e.g. shrimps and prawns from South-East Asia).
The Department of Veterinary Drugs, Hormones and Contaminants at the Institute for Food Safety in Vienna analyses nitrofuran metabolites and nitrofuran parent substances in a wide variety of sample types and is also the National Reference Laboratory for these tests.
- Liver (due to the higher concentrations and thus better detectability of nitrofuran metabolites in liver than in muscle, liver samples are taken from slaughtered animals within the scope of the NRKP)
- Aquaculture (shrimps, prawns, fish)
- Eggs and egg products
- Baby food and other foodstuff samples
- Animal feeds (since no metabolisation occurs here, the nitrofuran parent substances are analysed)
When processing samples, the covalently bound nitrofuran metabolites are released using mildly acidic hydrolysis.
Following derivatisation using nitrobenzaldehyde, the corresponding derivatives of AMOZ, AOZ, AHD and semicarbazide are measured using LC/MS/MS.
(In accordance with Commission Decision 2002/657/EC, a mass spectrometric method of confirming detection of prohibited substances is required.)
The detection thresholds are less than or equal to 0.1 µg/kg.
- Commission Regulation (EU) No. 37/2010 of 22 December 2009 concerning pharmacologically active substances and their classification regarding maximum residue limits in foodstuffs of animal origin (OJ. EU No. L 15 of 20/1/2010).
- ommission Decision 2003/181/EC of 13 March 2003 regarding the setting of minimum required performance limits (MRPLs) for certain residues in food of animal origin (OJ EU No L 71 of 15/03/2003).
- Commission Decision 2002/657/EC of 12 August 2002 implementing Council Directive 96/23/EC concerning the performance of analytical methods and the interpretation of results (OJ EC No L 221 of 17/8/2002).