The short answer is that all plastics have potential health hazards, but that most of them have few known or likely health hazards under normal, controlled use.
To avoid the potential for health hazards when using plastic, follow this simple rule: do not heat it. Do not microwave plastic, do not boil liquids inside of plastic, do not leave plastic exposed to the sun while it contains liquids. Also, do not store fatty foods in plastic, as toxins leach into the fat.
When heated, some types of plastic are known to release chemical toxins. Just because a toxin is not known to be released does not mean that all plastics are completely safe — only that we do not know whether they are unsafe.
To see the actual known health hazards of each type of plastic (as listed by its recycle code), please review my hub on the topic: http://hubpages.com/health/Safe-Plastics-Vs-Unsafe...