Hello!
A substance that could be found in air, water or soil that is harmful to humans or animals is a Pollutant.
The other substances cannot be found in air, water or soil. Fossil fuels can only be found in soil, smog can only be found in the air, and carbon dioxide can be found in the water or air.
Pollutants are substances that have harmful effects and damage the environment. Some examples of pollutants are Carbon Monoxide (air), Lead (soil) and Insecticides (water).
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