"You'd have to eat 500 burgers a day to even get a trace of this bute." David Dimbleby, Question Time, February 14, 2013
Widespread outrage over the presence of horse DNA in Tesco's burgers and Findus' lasagne has seemingly opened a Pandora's box of revelations about the food industry in Britain.
However on yesterday's BBC Question Time, host David Dimbleby suggested that the flurry of media stories about the presence of a drug called bute (full name: Phenylbutazone) in samples of the meat might be an over-reaction, given that you'd have to eat 500 burgers before the drug showed up in a human. Is this sound advice?
What is bute?
Bute is a drug that was originally developed in the late 1940s for the treatment of gout and rheumatoid arthritis in humans. Howevert has been banned for human use in the United Kingdom for over 20 years, but is commonly used as a pain killer in horses, dogs and other animals.
How are horses tested for bute?
EU legislation requires the UK to monitor residues of veterinary medicines in horses. This is run by the Chemicals Regulation Directorate of the Health and Safety Executive and the Veterinary Medicines Directorate. Since 2009, horse owners and keepers are required to identify each horse, pony or donkey with a passport, and to declare whether the horse is intended for human consumption.
Vets are advised to check the animal's identification before prescribing any medicine, and to assume that it is intended for human consumption if it doesn't hold a passport. Slaughtering an animal that has been given bute for food is an offence.
Is bute carcinogenic?
The Shadow Environment Secretary Mary Creagh revealed last month that she was in receipt of evidence "showing that several horses slaughtered by UK abattoirs last year tested positive for phenylbutazone —or bute—a drug that causes cancer in humans and that is banned from the human food chain." The presence of bute in horsemeat has since been confirmed.
The International Agency for Research on Cancer (part of the World Health Organisation) classifies it as a Group 3 substance, which means that it is "not classifiable as to its carcinogenicity to humans." This in turn means the evidence of carcinogenicity is inadequate in humans (see the definition here). This doesn't mean that bute is safe, but that there isn't enough evidence to say it causes cancer in humans.
However, adverse effects such as blood discrasia have been registered in past as a result of residues of bute entering the food chain. The Veterinary Residues Committee - an independent scientific advisory committee that advises the Government - has expressed concern over this risk last year.
How much bute is dangerous?
The Chief Medical Officer Sally Davies announced on the Deaprtment of Health's website that:
"at the levels of bute that have been found, a person would have to eat 500 to 600 burgers a day that are 100% horse meat to get close to consuming a human's daily dose. And it passes through the system fairly quickly, so it is unlikely to build up in our bodies."
Though it's safe to assume that eating 500 burgers in one day would be harmful in itself whether or not they contained any bute - Sally Davies also added that the levels found could be more harmful for "patients who have been taking phenylbutazone as a medicine" as it could have "serious side effects". She clarified that "it is extremely unlikely that anyone who has eaten horsemeat containing bute will experience one of these side effects."
How widespread is the problem in the UK?
Though horsemeat is not normally consumed in the UK, horses are regularly slaughtered in this country for human consumption in other countries, mostly within the European Union. According to Defra, "8,000 horses are slaughtered for human consumption every year in the UK", and over the last five years between 2-5% of horse samples have tested positive for residues of bute.
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