Cadmium

Cadmium was an element present on the planet Ribos, as the Magellanic Mining Conglomerate discovered in their geological survey of the planet. (TV: The Ribos Operation)

In the early 21st century, rain water had tiny but measurable amounts of cadmium, dioxin, lead and plutonium due to high pollution levels. (PROSE: Cat's Cradle: Warhead)