The daddy of them all in recent years has been global warming.You could literally list hundreds of baseless health scares that have circulated around. Chemo-phobia is pretty common in modern day, and as long as you use the big-word sounding name for things people will be afraid of it and think its toxic.
Some of these 'scares' have been worthwhile, such as the battle against pollution. A lot of it was over-hyped by fellows like Paul Ehrlich to the point where the predictions were just loopy, but littering (as a small example) did get under greater control through public education and, under Nixon, the government began the National Environmental Policy Act of 1969, Created the EPA in 1970 , the Clean Air Act Extension of 1970, the Marine Mammal Protection Act of 1972 , the Safe Drinking Water Act of 1974, and the Endangered Species Act of 1973.
Some of these agencies have gone out of control since then, as bureaucracies often do, but overall there had to be something done in all these areas. But for the most part these weren't 'scare stories', they were just public issues that had to be dealt with.