"Microplastics" is a term used to describe the tiny particles of plastic waste. The problem is that these don't break down organically - they just become smaller (to the molecular level). There's famously the "plastic soup" in oceans that contains such particles.
A recent Norwegian* study looked into the originators of these microplastic. Surprisingly enough: car tyres. There are other sources, but they contribute significantly less. According to the infographic, it breaks down as follows:
- Car tyres: 2250 tons
- Paint/maintenance of ships: 650 tons
- loss from plastic production: 400 tons
- painting/maintenance of buildings+infrastructure: 310 tons
- laundry: 110 tons
- waste treatment: 100 tons
... and some small change.
This means that car tyres alone, by themselves, account for a staggering 55% of microplastic waste.
To put this in perspective: Germans and Norwegians (both) use up about 2 kilos of car tyres per person per year.
Note: These numbers seem particular to Norway - overall yearly production of microplastics seems (unfortunately) vastly greater, see the below-linked German report (table on page 33) for some EU estimates.
* There's apparently a German study corroborating this. The only one I could find is here (English, downloads a PDF).
(Score: 3, Informative) by Zinho on Friday November 06 2015, @10:07PM
All of the black in care tires comes from Carbon black (i.e. soot) added to the rubber. The rubber by itself is a translucent tan. [google.com] By the time the rubber is floating in the ocean as monomolecular bits the carbon black is released and contributing to global warming on its own, as soot.
"Space Exploration is not endless circles in low earth orbit." -Buzz Aldrin