How negative an effect does cigarette smoking have on the environment?

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Personally, I think smoking's extremely harmful. It releases carbon monoxide and dioxide into the air, as well as multiple types of poisonous fumes in micro-amounts. After the butts are thrown away, they litter the ground on which we walk, looking but ugly and unhealthy. And they don't biodegrade like you would think. The dangerous chemicals in them cause them to break down much slower than normal, and to leech mercury and tar into the ground and water table. What are your thoughts? Am I way off?