Anti-plastic

Anti-plastic was a substance capable of causing significant harm to the Nestene Consciousness.

Characteristics
It was a blue liquid, created by various combinations of chlorofluorocarbons, vinyl acetates, copolymers, maleic anhydride, and ethyl alcohol. Anti-plastic interacted with the molecular structure of plastic and caused it to disintegrate. When put in water, it bonded with the polar hydrocarbon molecules, adhering to them and replicating itself throughout the water. (PROSE: Autonomy)

History
It was implied that anti-plastic was invented by the Doctor's former companion Ace as part of her work with A Charitable Earth. (PROSE: At Childhood's End) The Nestene Consciousness, however, believed that it was an alien weapon and could not be replicated by humans. (AUDIO: Armageddon)

When the Fifth Doctor asked if possessed any "anti-plastic" as part of his alliance with Autons, it was revealed he did, though he considered the name ridiculous. (AUDIO: The Auton Infinity)

The Seventh Doctor utilised a liquid to defeat the Nestenes, although he did not refer to it as anti-plastic. (COMIC: Plastic Millenium)

The Ninth Doctor carried the liquid around in a vial in his pocket. He had originally planned to use the anti-plastic as a threat and a bargaining chip to make the Consciousness leave Earth, which the Consciousness refused to do. Discovering the Doctor's TARDIS, the Consciousness had an Auton take the Doctor's anti-plastic from him, but Rose Tyler knocked it into the Consciousness whilst rescuing the Doctor. (TV: Rose) The anti-plastic very nearly destroyed the Nestene Consciousness, but a single "nugget" survived and possessed an Auton. (PROSE: Revenge of the Nestene) When the Tenth Doctor was stranded in 1969 and stumbled across the Nestene Consciousness, he cursed that his anti-plastic was a few decades in the future. (COMIC: A Little Help from My Friends)

A vial of anti-plastic, implied by Kate Stewart to have been provided by the Doctor, was possessed by UNIT and was secretly kept in Black Archive 5 which had been decomissioned in 2006. Recovering the vial from the archive, Kate brought it with her as a plan B for her confrontation with the Nestene Consciousness during its 2010s invasion. It was used to severely wound the Nestene Consciousness, but failed to defeat it. (AUDIO: Armageddon)

Behind the scenes
In the first level of the video game, K9: Deja Who, derived from the events of TV: Rose, K9 finds the vial of anti-plastic in London before using it to destroy the Nestene Consciousness.