Microplastics escape wastewater treatment plants and get into the soil, the rivers and ultimately into the oceans. Similarly, large pieces of plastic dumped in rivers make their way to the oceans where the combination of sunlight, waves and wind decompose and photodegrade the plastic into microplastic particles. Other pieces of plastic come from fishing boats and ships.

https://mission.cmaquarium.org/news/plastic-problem-inside-sea-turtles/

https://thisisplastics.com/wp-content/uploads/iStock-1036767280-2.jpg

These plastics and microplastics forever remain in the oceans and environment.