Chemicals with unknown toxicity form when polypropylene plastic is heated.

[Comment:  Polypropylene is used for dishwasher safe food containers and plastic carpeting, among other things.]

Chemicals with unknown toxicity form when polypropylene plastic is heated.
http://www.environmentalhealthnews.org/ehs/newscience/polypropylene-plastic-additives-break-down-with-heat

"New chemicals – with unknown toxic properties – are present after heating commercial polypropylene plastics during manufacturing."