[thsksbd]

Sure, but it works :) (except that one company that had a low quality membrane that leached ionomers, lol). Once plastics have leached off their manufacturing chemicals they really are very benign.

The membranes you mention are permeable, basically, only to water. Salt ions are pretty small - if the membrane blocks salt ions, they're going to block just about any molecule [1].

1. for the most part. You can have a molecule that dissolves in the polymer membrane and therefore gets through. A great example is polymer self-diffusion itself (fairly slow) and very short chains of the polymer (faster). But, generally, polymers don't like to mix with anything but themselves (see Flory-Huggins and DeGennes).