As far as I know the US does not have any legal or regulatory requirements on plastics in contact with food.
A quick google (yeah, I still use it :-P ) brought this up:
https://www.acplasticsinc.com/informationcenter/r/fda-approved-plastics-for-food-contact
and
https://www.fda.gov/food/food-ingredients-packaging/packaging-food-contact-substances-fcs
That's a list of what's approved, but that's not a standard. I'm not sure there is a standard, as in the substance is tested in various conditions and the amount of leeching into food is measured and limits set. If there are limits, they should reflect current science. For example, BPA is a known hormone disrupter. Any allowable limits should be back by double-blind clinical trials that establish proposed limits pose no risk to the consumer.
A bit of research shows BPA isn't present in the polyethylene used in envelopes for sous vide cooking. (BPA is only used in plastics labeled with a "7" in their recycling symbol apparently.) It also doesn't look like plasticizers are used in non-chlorinated polyethylene at all. Unreacted polyethylene is acetylene, a gas, and short strings of it shouldn't be as biologically reactive as carbon ring structures. So at least in this case I wouldn't worry too much. <shrug>
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