These are things like arsenic, mercury, cadmium, lead, selenium.

NPR: Coal Ash May Pose Health Hazard

Critics, however, say the mining operation will destroy forests in the area, contaminate groundwater and pollute the air with chemical substances like lead, mercury and arsenic.

BBC: Arsonists attack Hellas gold mine in northern Greece

More proof that seemingly earth-shaking findings (like, say, bacteria with arsenic in their DNA) are often not true but will make you wish Douglas Adams was around to write about them.

FORBES: No Virginia, There Are No Faster Than Light Neutrinos