I noticed that Bear grylls did the same thing in one of his episodes ... he boiled water in a plastic bottle over a campfire. It is an intriguing idea, but I wouldn't do it if i needed to drink hot water or make some tea. The risk of chemical contamination is too high. It might be OK if the hot water is for external use, or cleaning purposes.
other Pete
Every fruit, nut, and vegetable in existence contains "poisonous" chemicals. Assuming you have a functioning liver, the amount and type of chemicals you'd ingest from occasionally heating water in a plastic bottle won't harm you.
-Blast