Earth, The same planet where it was assumed that bubbling water through it in pulp mills would not cause it to escape into the environment and if it did, mercury does not react with anything so it would sink harmlessly to the bottom mud, so all those fish with mercury contamination probably got it leaching from rocks in the natural environment.
Earthlings be like… stupid.
It’s not even that deep.
Mercury works to do the industrial process we need doing. And then… there is no “then”. We get the stuff we need and nothing else matters.
When the fan became hit with definite severe mercury poisoning in northern Ontario, as I understood the process was - mecury in pulp and paper plants leached chemicals out of the paper very efficiently, and then they bubbled water through it to remove those chemicals so the mercury could be reused. So the mercury did not get flushed into the river., it was completely recycled for use. When the government inspected and said “so why are you missing so many tons of mercury from inventory?” the response was “maybe it leaked through cracks in the concrete floor into the ground under the plant… but it couldn’t be in the river.”
AFAIK the fish to this day are still not safe to eat.
I’ve seen the “not for human consumption” label on bags of birdseed as well, including ones that included things that humans eat, like sunflower seeds and peanuts. I always took it to mean that the facility where it was processed doesn’t necessarily meet the hygiene standards required of places that process human food. If you ate the sunflower seeds out of the birdseed bag you’ll probably be fine, but their safety can’t be guaranteed.
My wife used to work for a fish wholesaler. This is in the UK, so obviously regulations won’t be identical, but there’s a very complex system of stock storage conditions, delivery mechanisms and declarations of origins paperwork and checks that they have to follow at every stage of the fish’s journey. If any of those elements aren’t followed, then the products do not pass for human consumption, and will go for animal feed. I suspect that’s what is going on in the OP.
So they ‘might’ not harm you. Or they might.
I spent most of my life within a few miles of the Hudson River, now contaminated by General Electric’s discharge of PCBs (polychlorinated biphenyls).
There was a decade or so when you weren’t allowed to fish on the most contaminated section, then they said you could fish there, but don’t eat them, and it would be best to wear gloves taking them off the hook. Now I think the guidance is women younger than 50 and children younger than 15 can’t eat them, and everyone else can eat them once every couple of weeks.
It may be 50 years before it will be safe to consume them regularly.
I lived only a couple miles from the Hudson. It is much cleaner than it used to be, but I still wouldn’t eat fish from it.