PS is well known for leeching the plasticizer from PVC violently. It's why they bag the cables!
Back to front. Expanded PS foam doesn't change the diffusion rate of plasticizers out of PVC. It just has a very small amount of PS (thin foam cell walls) to melt, so the plasticizers have a far more dramatic effect on the PS foam.
Plasticizers are *everywhere*. A chemist friend of mine mentioned it's virtually impossible to prepare samples for gas or liquid chromatography, without them having plasticizers contamination.
And people wonder why there is a cancer epidemic.
The diffusing plasticizers effect I hate most, is the way photocopy toner on pages near the front and back covers of PVC ring binders, gets softened and transferred between paper surfaces. Also sticking the pages together.
Second most disgusting effect, is the way some types of aged cable insulation accumulates a tacky surface scum of concentrated plasticizers, which then becomes a dirt sponge, and also transfers to your skin if you handle the cables. Where it does what plasticizers are designed to do - dissolve into organic material and disrupt it's prior structure. Your cells in this case.
(ITT, I learned that web spell checkers consider the word plasticizer (singular) to be invalid.)