Your polyester shirt may soon come with a warning label. Lawmakers in California and New York have proposed state bills this year to raise awareness of a problem few consumers may have heard of — synthetic fabrics shedding microfibers into the water system. Reminiscent of the plastic microbeads that were banned from cosmetics, garments made with polymer-based cloth can release as many as 1,900 microfibers per wash that eventually end up in waterways, one study shows. But research is still at the early stages, and few are in agreement about what the best response is.