Mercury was a corrosive chemical element found on many planets, including Earth, Go-Ray and Skaro. Mercury could easily be found in any scientific community, particularly in labs. (TV: The Daleks ^[+]Terry Nation, Doctor Who season 1 (BBC tv, 1963-1964).)

Exposure to mercury had a negative effect on many species, as well as robots. A canister of mercury was used to corrode and disable a Gold Assassin who was on board a Roman sailing vessel. (COMIC: Golden Slumbers ^[+]Error: Code 2 - no data stored in variables, cache or SMW.)

Mercury poisoning was a common complaint among sailors. Amy Ivans, a passenger of the Lankester, was being poisoned with small doses of mercury, administered by Jacques De Requin. (AUDIO: Cryptobiosis ^[+]Elliot Thorpe, Bonus Releases (Big Finish Productions, 2005).)

Many devices required mercury to function. For example, on Go-Ray, the First Doctor, John and Gillian acquired mercury to repair a cardium reactor. (COMIC: Enter: The Go-Ray ^[+]Bill Mevin, TVC comic stories (1965).) When he first arrived on Skaro, the First Doctor, wanting to explore the Dalek City, falsely claimed that his TARDIS' fluid link K7 had run out of mercury as a ruse to explore the city. When he entertained the idea of building a new fluid link, he discovered that, ironically, his ship really did need more mercury. (TV: The Daleks ^[+]Terry Nation, Doctor Who season 1 (BBC tv, 1963-1964).)

The Second Doctor visited the Panjistri homeworld to stock up on mercury. (PROSE: Timewyrm: Apocalypse ^[+]Nigel Robinson, Virgin New Adventures (Virgin Books, 1991).) Later, the mercury in the fluid links evaporated, forcing the Doctor and Jamie McCrimmon to evacuate the TARDIS. The Doctor acquired more mercury on Space Station W3. (TV: The Wheel in Space ^[+]David Whitaker, Doctor Who season 5 (BBC1, 1968).)

The Fourth Doctor acquired some needed mercury in 1931 Chicago, unknowingly defeating the Master's plans by doing so. (PROSE: The Duke of Dominoes ^[+]Marc Platt, Decalog (Virgin Decalogs, Virgin Books, 1994).)

The Seventh Doctor stole some mercury from the Wierdarbi with the aid of Catherine Broome to refill the fluid links. (PROSE: Companion Piece ^[+]Robert Perry and Mike Tucker, Telos Doctor Who novellas (Telos Publishing, 2003).)

The Eighth Doctor visited a podule orbiting Jupiter in search of mercury for his TARDIS' fluid links. (PROSE: To the Slaughter ^[+]Stephen Cole, BBC Eighth Doctor Adventures (BBC Books, 2005).)

The planet Vulcan had mercury swamps on its surface. (TV: The Power of the Daleks ^[+]David Whitaker, Doctor Who season 4 (BBC1, 1966).) Skaro had geysers of mercury; the Dalek Emperor attempted to kill Zeg near one of them. (COMIC: Duel of the Daleks ^[+]unclear authorship, The Daleks comics (City Magazines, 1965).) The Acteon Galaxy had asteroids made of mercury. (AUDIO: Neverland ^[+]Alan Barnes, Main Range (Big Finish Productions, 2002).)

The Eighth Doctor visited Rontan 9 during the Last Great Time War in search of mercury to repair his TARDIS' fluid links. (PROSE: Natural Regression ^[+]Justin Richards, The Scientific Secrets of Doctor Who (2015).)