I bet it's a lot more widespread than Great Lakes water. I've seen stuff about microbeads appearing in just about all water. They're in so many consumer products, and can't be removed by water treatment systems, the stuff is showing up in any water source that's receiving any previously discharged water. That is, if it ain't rainwater, it's got plastic. Then again, if it is rainwater, it's got it's own menu of toxins, so ....
EDIT Wait, what, 12 breweries? Heck, there are that many just in Cleveland ....