>>>The air is on the outside all the time. And what happens with the change of water - the concentration of whatever it exudes suddenly drops to zero so it can start afresh? Then how much of that was in the water sold in it? That first water stayed in it for days or weeks.
>>
>>I honestly don't know, but think about entropy. Mayvbe the chemical exchanges slow down or stop when the water inside the bottle reaches a certain saturation or entropy level with whatever it's getting from the plastic while it sits there. Now introduce new water that has a much lower or even non-existent entropy level of whatever it is. Eventually, the plastic breaks down through the loss of 'whatever' to the point where it starts losing other components that the 'whatever' may have been keeping the plastic from losing.
>
>I'd rather not drink the whatever that's in the first fill of water. If it's so good at keeping the plastic stable, I'm not betting my guts that it's just as good for me.

There was some worry of hormone-similar stuff entering the water from plastic compared to glass 3 or 4 years ago -
tested on snails or shells IIRC - not connected to biphosphenate, which was more in stuff for babies.

Aged plastic probably is more prone to leak stuff - probably washing & cleaning would accelerate any such process,
if it does not follow the pattern of cloth-colour and washing machines.
Speculating that any special stabilizer is involved seems unnecessary.

regards

thomas