From Primary Microplastics in the Oceans: Boucher & Friot 2017
35% Clothing and textiles
28% Tyres
24% City dust
7% Road markings
3.7% Marine coatings
2% Beauty products
<1% Plastic nurdlesMy source is https://ourworldindata.org/uploads/2018/08/Great-Pacific-Gar..., which in turn sources its data from https://www.nature.com/articles/s41598-018-22939-w
The obvious issues are plastics breakdown at wildly different rates so the ratios of plastic pollution doesn’t match the ratios seen in the ocean. There are significant differences in where each type of plastic enters the ocean and where it ends up so sampling different parts of the ocean results in different observations. Finally sizes vary widely so measuring by volume, piece, or weight gives different results.
On top of this it’s not always easy to say the actual origin of a given piece was.