Now risk is a relative thing. There is never no risk. There is considerable risk if you walk to work/school. For the young road traffic accident is probably the greatest, for older people falling over is a definite risk! Particularly in the snow! However, try to avoid this risk and stay in bed all day and there is still risk. You would start to get bed sores and increase your probability of developing a thrombosis for starters!
So what's this got to do with
#Phenylbutazone ("bute")? Well because no one can ever say there is no risk all we can do is class it between slight, low medium, high, and smoking. You know apparently several people each per year from tripping on aerosol cans?
So what is the risk from phenylbutazone from horse-meat?
Well a little background first. It was first used, really, for arthritis. It is called a "non-steroidal anti-inflammatory" ("NSAID") drug. It was used in much the same way as aspirin, ibuprofen and paracetamol (acetaminophen the USA). [Paracetamol is not technically classed as an NSAID for any smart arses but its pretty similar.] There are several other newer ones and probably safer ones too. Paracetamol and aspirin can both be deadly of course, but they are still classed as safe and of course available off the shelf. Aspirin is most famously dangerous because it causes bleeding in the guts and paracetamol is surprisingly toxic to the liver.
So phenylbutazone is old now, but it was introduced as an alternative to these NSAIDS. It worked reasonably well and it did NOT tend to cause people to suddenly drop dead. However, it had side effects of course, some unusual blood disorders and gastric bleeding (just like most NSAIDs). After thousands of people had taken phenylbutazone, it started to be clear that actually the side effects and interactions were relatively greater than with other NSAIDs so its use declined. Then between about 1970's to the 1990s a series of studies showed it could be carcinogenic... i.e., cause cancer. This pretty much killed its widespread human use, but it is still used commonly in animals including... horses.
So how carcinogenic was it? Studies were based on both humans and rat studies: 600mg per day for 10 days was shown to cause the first signs
of possible mutations taking place (first signs of cancer)... in rats it was established to occur at about 50mg per kg (i.e., equivalent to about 2.5 grams in a person). It clears the system in a day or so.
So how risky is it?
Well yes, if you gave a horse the standard dose (about 1 gram) and then killed the horse within the day and ate it you would consume some phenylbutazone. If you ate a whole horse and did so each day for 10 consecutive days... (if you did not die from overeating) there would be the possibility of some blood damage and potential gastric injury.
If you ate your own body weight in horse-meat, each day for 10 days you should be fine. If you ate your own weight in horse-meat everyday for several months, the phenylbutazone could reach the sort of mildly toxic levels people were worried about when it exited the human market.
If you ate a 1Kg 100% horse burger everyday, and it was fully dosed with phenylbutazone from the slaughtered horses you would only really consume about 5mg of phenylbutazone yourself. That is way way below the effective or toxic levels and it would clear quickly. So rephrasing: that is roughly 0.1mg per Kg which is therefore 1/500x the dose that gave problems for rats.
Does 1/500 sounds like too close for comfort?
Don't believe it: 500x the stated dose of aspirin, paracetamol or MOST drugs would be fatal to you. Please don't try it!
So how dangerous is phenylbutazone in beef burger contamination?
...Disclaimer. This is my own personal opinion and it is sensible to accept whatever official governments advice emerges because this will include other safety factors. Also I expect that if the fraudsters who did this were prepared to swap horse-meat for beef they will have cut all sorts of other corners in terms of food hygiene and of particular concern to me.... animal welfare.