If you live in New York City and you eat a lot of fish then there's a good chance you have high mercury levels
Now in all honesty every time I do a haz mat job involving a chemical I haven't dealt with in a while, I have to hit the books and bone up on the health effects and the protective measures. While the amounts of mercury may seem tiny the effects can be severe as they approach established exposure limits. Common sense tells you to eat fish once or twice per month or (if you really love fish) change the type of fish you eat.
The effects of long term exposures can quite extreme. Hat makers of the 1800's dipped their fingertips in meucury to shape beaver skin hats popular at that time. With the brain damage mercury did there came the term "Mad as a Hatter". And that as Paul Harvey would say is the rest of the story.