[schiffern]

>inert foreign molecules

Problem is they're often not inert. The polymers may be, but the bisphenol plasticizers, UV stabilizers, dyes, brominated fire retardants, mold release agents, etc may not be, and they leach out over time.

[marcosdumay]

Do they become reactive inside of living beings? Or just outside due to UV catalyzed hydrolyze?

[schiffern]

The molecules I'm speaking of are already reactive. Again it's not just the bulk polymer, there are a bunch of "special ingredients" added to most plastics, plus contaminants introduced during recycling.

https://en.wikipedia.org/wiki/Category:Plastics_additives