Hi Shel,
all plastics have residual polymer reactants and additives that are not necessary locked in and can leach out. One notable compound that has caught the attention of the media is Bisphenol A.
Bisphenol A - Wikipedia, the free encyclopedia
There are others.
The food and packaging industry has tried to solve this problem by making High Density PolyEthylene (HDPE) which is considered one of the most cost efficient and least reactive (or leaching) plastics hence approved for food use.
Plastic will never by as inert (unreactive) as glass or stainless steel. I do not consider it a major concern but I do have a tendency of purchasing EVOO in cans only and veggy oil in glass. The whole industry has converted to plastic so that every time you eat food service, the oil used was stored in a bucket.
Luc