Vodium was a type of mineral that produced energy that could be used in low-waste nuclear reactors and could create micro-wormholes. Acid, specifically citric acid, slowed down the reaction and the production of wormholes.
In the 21st century some vodium came to Earth and was found by Wanda Rothman's team. They started studying it and its potential for nuclear power. In 2010, Wanda was demonstrating it at a conference when it started producing wormholes, pulling in several people. Wanda, however, didn't realise the connection, gave a sample to Michael Neil and stored the rest in the hotel vault. When the Eighth Doctor found out, he and his friends helped neutralise it. Asha Qureshi, Rafshaw and Leonard Pallister neutralised Michael's sample, though they were too slow to save Leonard from being pulled in. The rest was neutralised by the Doctor and Hugh Bainbridge. (AUDIO: Situation Vacant)