The research today comes from Harold Johnson, a Saco, Maine, journalist and author of The Flotsam Diaries blog.
Johnson, who's outspoken of his criticism of the plastics industry, was nonetheless skeptical of the number, which he wrote "keeps cropping up, on personal blogs, nonprofit Web sites, popular scientific eZines, press releases."
(Plastics News has mentioned the number a few times, most prominently in coverage of a 2006 conference on plastic debris and the oceans.)
Johnson, writing in a guest blog for Scientific American, said something bothered him about the number.
"It's too round. Too easy. Too 'everywhere.' The vanilla ice cream of heartstring-tugging environmentalism," Johnson wrote.
So he set out to find the source -- and determine if it's worth repeating.
Johnson's research took him all the way back to a December 1984 story from The New York Times, "Deadly Tide of Plastic Waste Threatens World's Oceans and Aquatic Life." The story cited its source: a report from a group called The Entanglement Network at a November 1984 Workshop on the Fate and Impact of Marine Debris in Honolulu.
The Entanglement Network's report itself, from the conference's proceedings (PDF) does not cite the 100,000 figure.
"And just like that, I had the answer," Johnson wrote. "A 'fact' handed down & bandied about from article to nonprofit, conservation society to international organization, over years and years. So long that it has taken a life of its own, and becomes unquestioned, and unsourced. Whether there is -- or was -- any science behind it remains in doubt."
And, as he points out, even if it was accurate in 1984, it's out of date.
Marine debris is clearly a significant problem. But it is a magnet for hyperbole. We've seen that before in descriptions of the North Pacific Central Gyre that imply it is an actual floating island. And we've seen other exaggerated reports on the threats to marine life.
As Johnson wrote today, just because you see a 'fact' in 100 places, doesn't make it true.
But don't be surprised if, a year from now, you see it another 100 times.