Cigarette filters, do they really help?

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With much talk about the ill effects of smoking, I have been thinking if filters really lessen the risk, anybody made a study if those filters add harm or are toxic? I was also thinking of the environmental impact, smoke is bad enough but where would all those billions of filters go? Are they biodegradable? They carry some of the bad chemicals of tobacco, so if we just throw them anywhere then what do you think will happen?