> Bags are clearly on their way out, being replaced by cardboard bags.

In your city, maybe. Absolutely not globally

Disposable bags in the west contaminating the water? I would be immensely surprised if that's even 1% of clothes and shampoos/beauty products. We don't normally put plastic backs in running water for ages.

Yes. Thin disposable bags are easily degraded mechanically, resulting in lots of microparticles.

For clothes it's even worse, they produce microparticles at all times, especially during laundry.

Thin plastic bags in the west have a very short lifecycle that goes mostly shop->home->bin->landfill (segregated from water table). There is almost no opportunity for it to actually contaminate the water.