And Danceronice, if the drug is fat soluble, iirc, those are the drugs that do stay and accumulates in fat tissues [brain, breasts, ovaries, testes,...] in the animal and then in the animal that consumes that animal. I gets stored and stays there in the one, then in the consumer.
If you consume this meat item say once a week for life, and it has the drug in it... that is going to build up in ya'.
Think Mercury in fish. Bigger fish are more dangerous to consume cause they eat lots and lots of smaller fish laden with mercury. The higher up ion the food chain you go the more dangerous it is to consume as the drug is more concentrated due to their diet.
Say you have a concentration of something at 1% in water... move up the food chain 10 levels and it's not 10x worse... it's a million. It's an exponential equation.
Tuna being an apex predator means that they have a much higher concentration than the fish they eat... thus eat it yourself in moderation.
Furthermore, in my research into Bute I found some suggestions that one of the concerns is not that phenylbutazolidone is the 'issue' [though it is] for human consumption but that in horses it becomes a metabolite, iirc Oxybutazolidone, and that is WAY worse for humans.
It would be nice if these things were simple and black and white. But when you're talking drugs and bodies, it rarely ever is.