Pollution was the contamination of the environment by harmful substances, usually caused by industrial activity.
In the 1970s, a rise in ecological consciousness produced several anti-pollution activists. Clifford Jones protested the opening of the Global Chemicals oil refinery in Llanfairfach, which was later found to be dumping lethal toxic waste into the abandoned coal mine and was shut down. (TV: The Green Death) Sir Charles Grover formed Operation Golden Age to return Earth to its pre-industrial state. (TV: Invasion of the Dinosaurs) Professor J. P. Kettlewell developed pollution-free technologies such as a solar battery and a metal virus that would break down metal waste into easily recyclable form. (TV: Robot)
In the early 21st century, industrial pollution was so severe that the planet was reaching the point of no return. The Butler Institute planned to save humanity from the environmental collapse by uploading copies of their minds into computers. The Seventh Doctor and Ace put a stop to this, forcing the world's business corporations to instead fund a massive environmental clean-up program. (PROSE: Cat's Cradle: Warhead)
By 2050, pollution had made Britain on average three degrees warmer that it had been in the Middle Ages, and all the oak trees and birches had been cut down or died out. (TV: The Last Oak Tree) That year, Inspector Drake polluted the River Thames with chenium, but this was cleaned up by the Medes. (TV: Alien Avatar)