The substance is a chemical abbreviated as BPA and is called bisphenol A. It's been used in certain plastics since the 1950's to prevent them from getting hard and cracking. It's also used in lots of other things like the expoxy linings inside food cans. It's been link to a bunch of bad things but the FDA still claims it's safe even after banning it from baby bottles and sippy cups in 2012.

Lots of stuff we use contains BPA, well almost everything. Some plastic products claim they are BPA free but have only been replaced with other chemicals they say are just as bad. Don't lose any sleep over it, if it does cause problems the damage is already done.

If you are really concerned, you could freeze your tomatoes in glass jars. I save any glass jars from pickles, pasta sauce, etc. to use for dehydrated foods or things like horseradish and seasonal candied chestnuts, that I keep in the freezer. You can even go to your local recycling center and pick up glass jars for free. They're easy enough to scrub out and/or boil to sterilize.

Martha

We use ziplock bags for freezing our tomatoes, they make it easy to squeeze out the air pockets before sealing which helps in reducing freezer burn.

Plastic isn't airtight, tho. I use glass jars. I learned the hard way to fill them about 1 1/2" below the top, and to leave the lids loose until after the contents are frozen solid.