Pollution was the insertion toxic or otherwise non-native materials into an ecosystem.
Spock was able to confirm the arrival of the HMS Bounty in the late 20th century due to the high pollution content of the atmosphere. (Star Trek IV: The Voyage Home)
The Tagrans of Tagra IV requested assistance from the United Federation of Planets to help repair the ecological damage to their homeworld caused by pollution. (TNG: "True Q")
The technologically-advanced race of Ledos was found to be polluting the area of a more primitive species that was their genetic ancestors, the Ventu. (VOY: "Natural Law")
The Malons built an entire industry devoted to the disposal of industrial byproducts such as antimatter waste. This hazardous waste was dumped into open space. (VOY: "Night")