Their article states that researchers from the International Union for Conservation of Nature (IUCN) reviewed data from seven global regions. Their report found that between 15% and 31% of plastic pollution came from primary micro plastics.

"We discovered that most of the microplastics are coming from either the clothes or from the tyres. Microplastics are going everywhere in the sea and into the food chain, let's close the plastic tap."
François Simard. Deputy Director, IUCN's marine programme