I've been reading the wikipedia article, not through all of it yet.

https://en.wikipedia.org/wiki/Microplastics

Some highlights:
Bottled water has much higher microplastics content than tap water.

Coral can ingest microplastics

Waste water treatment plants filter out most (but not all) microbeads into sludge. Some places use that sludge as fertilizer for farms.

Microplastics are in stuff you would not guess. Paper coffee cups have a plastic liner. Clothes put off large amounts of microplastics when washed. Tires put off microplastics. Some exfoliants and other cosmetics contain microplastics as microbeads.