PET (polyethylene terephthalate) is a plastic hardening material(to make the bottle more rigid) a, it's been used for chemical container(to stop been dissolving) etc etc. I don't think it can lead to cancer, otherwise it has to be labeled for legal reason.
I have heard that it might lead to endocrine disruption, nothing more.
plus, the numbers 1to7(no 8!!= =b) is resin identification code. they've been used for recycling purposes, not based on toxicity a...
don't know where LZ get the idea of 2=unhealthy....{:4_119:}
anyway, hope it helps.{:4_107:}
+ number 5 would be more rigid than number 2(i think), maybe that's why it's been used with hot water for safty reason.