Are you certain the barrels are made of polypropylene?
Bic pens are composed from polystyrene in their barrels for example, being the most sold pen in the world I'd take note and carefully research whether you've been looking at the materials list for the correct part.
For example, polystyrene meets the stringent standards of the U.S. Food and Drug Administration and the European Commission/European Food Safety Authority for use in packaging to store and serve food. The Hong Kong Food and Environmental Hygiene Department recently reviewed the safety of serving various foods in polystyrene foodservice products and reached the same conclusion as the U.S. FDA.[108]https://en.wikipedia.org/wiki/Polystyrene#Safety
