Explain pollution to a visitor from another planet

Visitor from another planet:
First off I'd like to say welcome to　planet earth. I am pleased to introduce myself as your host and welcome to my beloved planet. You can also think of me as your informant. I will tell you all you need to know about my planet including one if the most terrible things that happens here on earth called pollution. Before I continue, I feel like I should go in depth and explain to you this thing called pollution. Well to give you a bit of a　definition of pollution　which is it is the introduction of harmful substances or products into the environment such as air or water. Things that pollute air and water are relatively pretty harmless like when people throw their trash into the ocean or rivers, or when people spray perfume or cologne while trying to freshen themselves up a bit. While those things are somewhat harmless to us humans, there are things that aren't. Some things like cigarette smoke. Cigarettes are little sticks of a drug called tobacco and people smoke them. They are terrible for our lungs but people do it anyways and not only do they hurt themselves but they hurt people who are around them. The smoke that comes from the cigarette pollutes the air and people close enough can breathe it in. It's a deadly toxin and can even kill people with a disease called lung cancer.