Little white particles floating in my water bottles after freezing and thawing? Safe to drink still?

I had a flat of plastic water bottles in the trunk of my car and they all froze. Now that they've thawed there are little white particles (kind of look like fuzz) floating around in the bottles. Does anyone know if this a build up of minerals caused by the freezing or is it part of the plastic bottle, or something different? I'm wondering if they're safe to drink still. (The bottles have never been opened so it's not something I could have put into the water).