Seafood and drug residue

The worldwide food and drink industry is one of the largest of the manufacturing sectors. It is the largest within the UK, accounting for 15% of all manufacturing and a total turnover of over £70bn (1), which ranks the UK's food and drink industry as fourth in the world (2). Spending on food and drink increases year after year, accounting for a large percentage of customer expenditure. As such a large industry, this sector employs 13% of the UK manufacturing workforce alone (1).

Following BSE and Foot and Mouth disease food scares in recent years, consumers are becoming increasingly aware of food contamination and the existence of veterinary drug residues, microbiological contamination, mycotoxins, pesticides and disease carry-over implications of food. A large food analysis testing market exists, with a wide range of tests available. Drug residue testing has been regularly tested under government initiatives since the early 1980s, when reports confirmed the potential damage residues could cause to human health. Drug residue testing is performed in public and private laboratories, with many large retail chains and producers creating in-house laboratories.

Seafood accounts for a portion of the food industry along with meat, honey and dairy. Although a smaller portion of the mix, seafood testing is crucial as evidenced by recent reports of contaminated shrimp from Bangladesh that was reported to contain nitrofurans and chloramphenicol. The UK seafood market was worth approximately £5.2bn in 2004 (3). Salmon has the largest farm fish value in the UK (4) with an estimated retail value of over £700m in 2004 (3).

UK aquaculture produce have recently proved they are free from all drug residues with zero positive samples detected, however, it is important to note that this does not mean that all seafood in stores is safe. Rigorous food analysis in conjunction with effective drug residue testing must take place worldwide. It is not enough to know that the seafood produced in our respective countries is safe due the high amount of importing and exporting, the food on our shelves may well be contaminated.

Drug residue food analysis laboratories require reliable and accurate testing as well as cost-effective screening methods. Drug residue screening in seafood should include the following the following compounds:

Quinolones are a group of synthetic antimicrobials that inhibit the activity of bacterial DNA gyrase enzymes. The earliest members of this group of compounds are active against gram-negative bacteria. The newer fluoroquinolone antibiotics, a fluorine-containing subclass of the quinolones, have been found to have enhanced antibacterial activity against gram-negative bacteria and they are also active against gram-positive bacteria.

Chloramphenicol is a broad spectrum antibiotic isolated from the soil bacterium Streptomyces venezuela. It is bacteriostatic in action and inhibits bacterial protein synthesis by binding to the ribosomal 50S subunit. Chloramphenicol has been used to treat a wide range of human and animal conditions.

Malachite green is a triphenylmethane dye which is used extensively in the aquaculture industry for the treatment of fungal and protozoal infections (5). The toxicity of the dye increases with exposure time, temperature and concentration and has been reported to cause carcinogenesis, mutagenesis, chromosomal fractures, teratogenicity and respiratory toxicity (6). Malachite green has a high level of abuse due to its efficacy and the lack of equally effective alternatives. (7) It is easily absorbed during waterborne exposure (3) and metabolised to the colourless compound, leucomalachite green, which can persist in fatty fish tissue for long periods of time. (8).

Nitrofurans have been widely used in veterinary practice as antibacterial agents in the treatment of pigs, poultry, fish and shrimp. Bans on nitrofurans were introduced within the EU primarily because of concerns about their carcinogenicity and mutagenicity. Several other Non-European countries have also banned all uses of nitrofurans in food producing animals.

Ivermectin is a broad spectrum anti-parasitic agent and is widely used in human and animal medicine. It is used for treating sea lice infestation of farmed fish. Residues of Ivermectin can persist in fish tissue for long periods of time, therefore can cause a potential risk to human health.

Sulphonamides are synthetic bacteriostatic antimicrobial agents with a wide antibacterial spectrum encompassing most gram positive and many gram negative organisms. They are widely used for the therapeutic and prophylactic treatment of animal diseases. World wide there are concerns that the widespread use of antibiotics such as these Sulphonamides would result in a toxic or allergic reaction or the possible development of resistance factors in the human population.

1. David Boothley, et al., 2007, 'Research into UK Food and Drink Manufacturing', ADAS UK Ltd

2. Defra website, 2009, www.defra.gov.uk

3. Seafood Choice Alliances, April 2007, 'The UK Marketplace for Sustainable Seafood'

4. Steve R. Knight, 2006, 'Fishery Products, Annual Report', USDA Foreign Agricultural Service, GAIN report

5. Tarbin, Jonathon A. et al, (1998) The Analyst, 123, 2567-2571.

6. Srivasta S., Sinha R., and Roy D., (2004) Toxicological effects of malachite green. Aquat Toxicol. 66(3): 319-29.

7. Mitrowska, A., Posyniak A., Zmudski J., (2006) J. Vet. Pharmacol. Therap. 29 (Suppl. 1), 173.

8. Turnipseed, Sherri B., Andersen, Wendy C., Roybal Jose E., (2004) Laboratory Information Bulletin Vol 20, No.11