As many as six horse carcasses that tested positive for the equine drug bute may have entered the human food chain in France, the British government said Thursday.

Britain’s Environment Minister David Heath told the House of Commons that eight horses from British abattoirs had tested positive for the equine painkiller and anti-inflammatory known as “bute”, and six were sent to France and may have entered the food chain.

Britain's Food Standards Agency said it was working with French officials to trace the meat.

Horsemeat itself is not dangerous to eat. But “bute,” or phenylbutazone, is considered potentially harmful to humans.

The drug can cause a potentially fatal blood disorder in humans called aplastic anaemia, in which the bone marrow fails to produce enough new blood cells. It has also been linked to kidney, cardiovascular and gastrointestinal problems in humans.

Britain's chief medical officer, Sally Davies, insists that any horsemeat containing phenylbutazone "presents a very low risk to human health” and that "it is extremely unlikely that anyone who has eaten horsemeat containing bute will experience one of these side effects."

She explained that someone would have to eat 500 to 600 pure horsemeat burgers to be at risk.

"It would really be difficult to get up to a human dose,” she said Thursday.

Until now, the horsemeat scandal has largely been an issue of consumer deception. While thousands of horses are slaughtered in the U.K. every year, most of that meat is exported to other countries to be sold in specialty butcher shops. In Britain, most consumers consider eating horsemeat taboo.

Since British authorities first discovered horsemeat in processed food last month, millions of burgers and frozen meals have been recalled across Europe.

CTV’s Janis Mackey-Frayer says meat suppliers likely tried to sneak horsemeat into the British beef supply because horsemeat is simply cheaper to produce.

“There are much more stringent documentation rules when it comes to beef. A side of beef effectively has its own passport,” she told CTV’s Canada AM Thursday.

“A butcher can tell a consumer what farm it was raised on, when it went to slaughter, its date of birth – everything. There isn’t that same sort of traceability with other types of meat.”

Authorities are still struggling to figure out how the horsemeat got into supermarket and fast-food burgers and frozen dinners.

Processed foods in Europe do not need to be labeled by their countries of origin, so typical frozen meals can have ingredients from all over.

In Paris, French Economic and Consumer Affairs Minister Benoit Hamon said it appeared that the fraudulent sales had been going on for several months, and reached across 13 countries and 28 companies.

He said most of the blame likely rested with Spanghero, a French wholesaler he said must have been aware that the cheap meat was mislabelled when it sold it the product on to Comigel, a frozen food processor.

"Spanghero knew," Hamon said. "One thing that should have attracted Spanghero's attention? The price."

Hamon said the mislabelled meat would have been priced far below the market rate for beef. As well, he said, the smell and colour of the meat should have been tipoffs.

With reports from the Associated Press