The flawed premise is that synthetic clothing significantly contributes to microplastic pollution, particularly in the ocean. Plastic pollution in the ocean comes primarily from fishing gear like nets, debris unintentionally released by major storms and wave events, and countries that use rivers leading to the ocean as primary waste disposal. If you want to make a difference to plastic pollution, advocate for sustainable fishing practices, end shipping waste overseas for fake recycling (Patagonia really recycling helps this), and support programs to establish waste collection and disposal in countries that don't have it.
Standard sewage treatment processes also capture most microplastic with the solid waste, if you live somewhere with sewage treatment.
Standard sewage treatment processes also capture most microplastic with the solid waste, if you live somewhere with sewage treatment.