Too much, in the wrong place
What Makes Something Pollution?
Nothing is pollution on its own. It becomes pollution when there is too much of it somewhere it does not belong.
-
Step 1 of 5
Most pollutants are ordinary things.
The fish are killed by the algae the manure feeds, not by the manure. Cow manure on a field is fertiliser. The same manure in a stream kills the fish. Nothing changed about the manure, only where it ended up.
-
Step 2 of 5
Nature deals with small amounts all the time.
Bacteria break things down, rain dilutes them, wind carries them off. That handling capacity is real but it has a limit.
-
Step 3 of 5
Pollution starts where the arriving beats the handling.
One house's smoke drifts away. A city's smoke sits in the valley until it stings your eyes. The switch is the amount, not the substance.
-
Step 4 of 5
Some things cannot be broken down at all.
Lead, mercury and many plastics have no bacteria that eat them. They do not disappear — they simply move around and collect.
-
Step 5 of 5
Which is why there is no such place as away.
Everything thrown out lands somewhere: in a river, in the air, in the soil, in something's body. The question is only whose somewhere it becomes.
Heat, light and sound are pollution too. A river warmed by a power station holds less oxygen, and a lit sky stops birds navigating.
The short version
Pollution is not a kind of stuff but a mismatch: more of something arriving in a place than that place can break down or carry away.
Try it yourself
Put one drop of ink in a bath and then twenty in a cup. The bath copes and the cup does not, with the same ink.