There is mercury in our food suply and always has been.
It is a part of the environment with or without mankind.
One single vent on any of the worlds active volcanos typically vents 2 tons per year into the atmosphere.
A crisis can be created, however, by informing the public of something they didn’t know about and prevaricating about the cause.
Yeah, and doubling the amount of a contaminant from the natural baseline has no effect. </sarc>
Even if we're adapted to the environmental levels, that doesn't mean doubling it has no effect. Oxygen is natural and has always been in our atmosphere, too, but if you double the concentration from about 20% to 40%, you'll notice effects on humans.