Addendum to my plastics post from 6/30/09:
After some random research I found that plastic #6 isn't safe after all =(
"#6: Polystyrene is a concern because the chemical styrene can leach into food and beverages. According to the EPA, short-term styrene exposure at levels above the Maximum Contaminant Level (used to set drinking-water standards) can cause nervous-system effects such as loss of concentration, weakness, and nausea. Long-term exposure can cause liver and nerve damage and cancer." Found from the Common Ground website, confirmed from other research studies found on the web.
The good news is that #5pp is a safe choice as well. I have read that #5 can contain BPA, but not #5pp.
So, I'll be sticking to 1, 2, 4 & 5pp for now! But remember- never heat in plastic- only store food in it.