[IfOnlyYouKnew]

Tar, and other tobacco detritus, isn't really dangerous: The asphalt it's lying on is actually very similar, chemically.

Cigarette butts without the filter are easily degraded organic (carbon) compounds. You can compost them and will get perfectly acceptable potting soil.

Same story for the various additives. As a rule, anything that has a physiological effect and isn't a heavy metal is biodegradable.