The word 'pollution' should be thought of in the same way as the word 'corruption'. The introduction of the undesirable.
(Cracking knuckles, clearing throat)
When any entity (animal, vegetable or mineral) or element (liquid, solid or gas) is loosed into an environment in which it was neither formed nor intended, corruption (pollution) of that environment is almost inevitable. We use the term 'pollution' to describe the by-products of processes- trash, smoke, unsightliness, etc; but what you really have is material corruption of the natural (or working) balance of the surroundings.