I love Chubbyemu's youtube channel. He's a toxicologist who switched to medicine. If you like criminal documentaries JCS Criminal Psychology is great too. Cold Fusion for business stories.
The main source of mercury for laymen is large fish, most commonly tuna and salmon. Nutritionists recommend limiting large fish consumption to one serving per week for tuna and other large fish. Small fish like sardines, and most mackeral are not restricted.