About thirty years ago I read an article in the Wall Street Journal about experiments with oil-eating bacteria--perhaps they could be tweaked to clean up oil spills. (And in fact, they have been used in some recent spills.) My immediate thought was, "Great--but what happens if your car catches it?" This premise became the background for some sf books I wrote that I will mention on a different board.
I actually think now that the most likely cause for the collapse of civilization is climate change. Perhaps not the climate itself, but the immense societal dislocations it will cause.