Case 2 is an interesting case, it's a startlingly widespread fear yet seems ridiculous when you think about it for more than a few seconds. Slate Star Codex concluded it's alarmism sparked in the 80s by the media's coverage of the Mobro 4000 trash barge.

https://en.wikipedia.org/wiki/Mobro_4000

Point 5 ("5. More And More Trash Piling Up Until The Whole World Is Just A Giant Mountain Of Trash"): https://web.archive.org/web/20190102054648/https://slatestar...