There is no universal definition of pollution that I know of, so let me suggest one. First, I have to define terms.
Ecology is the study of ecosystem.
This would include noise, nuclear radiation, cigarette butts, and so on. Algae cloud the water, and cause some fish to die, others to increase in number. For sufficiently small amounts of sufficiently innocuous pollutants, the ecosystem's feedback loops will restore the previous balance in time. This is called pollution. Other times, it goes completely to pieces, and what's left is a lump of dirt or rock.