The BBC Horizons documentary I mentioned above also looked into mussels as a source of meat. I don't recall pollution being mentioned as an issue, but it gave other reasons why even optimistic outlooks could only consider them a partial replacement, given the numbers we have for meat consumption today (not to mention decades from now).

I don't - offhand. Back when I was taking classes in it, the industry was collapsing in China because of water pollution. I have been reading about blue-green algae tides and chemical spills and other issues affecting the industry these days, but I don't have a specific source detailing its impact. Sorry. (Good one for calling me out on that!)