Rust has no reason to touch the original Unix API. Take a snapshot of the values at startup and write an API around that, any runtime modification of the Unix environment is suspect anyway and anyone who wants to deal with that rotten mess can jump through half a dozen hoops.

> Rust is doing everything it can here, these APIs are labelled unsafe

Unix gave us C, clearly Rust should have just labeled every C standard library function like malloc and free unsafe and thrown up their hands instead of introducing ownership semantics and all that messy compiler logic around it. After all Rust can't fix how Unix works, so they shouldn't have tried in the first place.