Everybody is chemical conscious now days and we read about all the bad stuff in wax foundation. Some of these chemicals get introduced to the wax through treatments for various diseases, but I think a much larger portion of it is introduced on the bees themselves. As they forage the pick up what ever herbicides and pesticides are sprayed and applied around the places they forage...

These compounds are transported back to the colony in minute amounts over time and build up in the comb of the hive. Until we remove that wax and make something else out of it. So we may be polluting our own homes with the very compounds we don't want in our hives.