Residues in trout persist

Data collected by the UK’s Veterinary Medicines Directorate has revealed the presence of malachite green (MG) and leucomalachite green (LMG) in farmed fish. Government officials have been concerned for some time but residues continue to be found. 

In spite of attempts to reduce residues of unregistered or unauthorised chemicals, the latest research shows eight samples out of 70 contain residues of LMG, and two of these also contained MG(1). MG has never been authorised as a veterinary medicine (a chemical used to control veterinary pests and diseases). It has industrial/chemical uses including as a dye, and as an acid-base indicator. LMG exists as a chemical in its own right but is mainly found as the major metabolite of MG. Because the chemical is not authorised, there are no maximum residue levels set for trout. 
    The lack of authorised veterinary products available for use in the trout industry has meant that for many years producers have opted to use MG. Fish farmers had noticed, probably by accident, that it had particular curative properties.
    In 1993, and the again in 1998, the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) expressed its concern about the presence of MG residues in farmed trout. COT said that: ‘this material has not been proved safe for use in fish farming’(2).
    The Committee on Mutagenicity (COM) has also concluded that MG may be a mutagen (a chemical that increases genetic mutations by causing changes in DNA). Long-term animal cancer tests on MG and LMG are underway in the US, and due for publication in 2002(3). 
    Officials at the Ministry of Agriculture, Fisheries and Food (MAFF) met with the British Trout Association and, in February 2000, revised guidelines in an attempt to reduce MG and LMG levels in trout. Unfortunately residues are still being found. In April 2000 the government’s Food Standards Agency (FSA) came into force in order to help solve food safety problems (see page 14). At an October 2000 meeting, the FSA expressed concern over the continued presence of MG and LMG. 
    If the US cancer tests prove positive, then stronger action will have to be taken. 
    The industry does not have a safe chemical that can be used for treatment of the parasitic and fungal diseases. Some environmentalists are concerned about the intensive nature of fish farming.

References
1. The Veterinary Medicines Directorate, Annual Report on Surveillance for Veterinary Residues, July 2000 p34, www.vmd.gov.uk.
2. Ibid.
3. FSA News, Jan. 2001, www.foodstandards.gov.uk.

[This article first appeared in Pesticides News No.51, March 2001, p16]