I have recently taken an interest in food grade plastics and I found this list. Plastic bottles and containers usually have a number embossed on the bottom, and the list explains what each number means. Don’t use #6 or #7 for storing food, as they can seep harmful hormone disruptors into your food.

http://www.checnet.org/healtheHouse/education/quicklist-detail.asp?Main_ID=353

Also, microwave cooking seems to be a catalyst for chemical seepage. Do not cook frozen foods (ex: Frozen Burritos) in their original wrappers (I have been unknowingly doing this for years). They are not meant for microwave cooking, and it is said that thousands of harmful carcinogens seep into the food during a microwave heat up. Instead, use a glass plate or a paper towel.

Some plastic packaging that is intended for microwaving food is ok, but said to still seep chemicals into the foods. These ‘food-safe’ chemicals are not known to be harmful, but they are still lurking around in your TV dinner.

Hope this is helpful!