 No mercury level may be truly safe. This review on the adverse effects of mercury in fish suggested that even slightly increased environmental exposure to methylmercury from fish could lead to adverse effects on nervous system development, just like lead exposure. No lead is the only good lead, and the same is true for mercury. They pointed to this famous study published in the Journal of Pediatrics a few years ago showing delayed brainstem auditory evoked potential latencies in teens exposed to methylmercury as an objective measure of neurobehavioral toxicity in 14-year-old children with developmental exposure to methylmercury from fish. It's a measure of how well the nerves in your brain communicate. You take kids, you stick electrodes on their scalp and headphones on their ears, and play a quick sound. And then just measure how long it takes for that sound to be transmitted from the nerves in their ear to the auditory cortex in their brain. The longer the delay, the slower your nerve impulses are traveling. And so here's the graph. This is delay versus mercury content in their hair. You'll notice two things. The more mercury the kids had in their bodies, the longer the delay. That's bad. Also you'll notice it's basically a straight line. It doesn't plateau out at the bottom end. The lower the mercury, the better. Where do the official safety limits fit on this graph? In 1978, the World Health Organization started to realize how dangerous mercury was, so they said no greater than this level is safe. We didn't know any better. Decades later, the quote-unquote safe upper limit was moved down to here. Our government said no way. Our children are much too precious for that and placed our upper limit here in 2001. As you can plainly see from this later data though, if you push levels lower, get people to eat less fish, you get even less brain damage. Yet as of 2012, the safety limit remains there. As one former EPA toxicologist told The Wall Street Journal, government regulators really consider the fish industry to be their clients rather than the US public.