PET bottles = risk for cancer ?

I was talkin` with some medicine students a couple of days ago, and they told me something rather interresting : PET bottles with liquids containing CO2 (charbon dioxide), and I`m refferring to mineral water plastic bottles, or juice plastic bottles, if not consumed in 6 months , they develop cancerigen substances, due to the interaction between CO2 and the plastic material of the bottle.

So, if you have a PET bottle with mineral water older than six months, the odds to develop cancer are bigger.

I`m not sayin` this is true, I don`t have the knowledge in chemistry to say it`s true or not. Those friends of mine told me they KNOW it`s true, but I need some opinions on this from people who work with chemical substances, or at least know what and if this is possible, theoretically speaking.